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The text and illustrations of this article are from Organic Gardening and Farming; October 1973.

By Philip and Joyce Mahan

After some study and experimentation, we have set up a productive food chain– table scraps to earthworms to catfish–in our backyard. The project is satisfactory in many respects, utilizing waste materials to produce fresh fish for food and at the same time yielding ample compost for a small garden. The material cost is minimal. The whole operation can be set up for less that $15.00. The equipment occupies only about 12 square feet of space, and the entire assembly can be easily moved if necessary.

The materials can be very simple: Two 55-gallon steel drums, three panes of glass 24 inches square, and a medium-sized aquarium air pump. One of the drums will serve as a tank for the fish, oxygen being supplied by the air pump, and the second drum should be cut in half to provide two bins for the worms. The panes of glass are used as covers for the worm bins and fish tank, and for ease and safety in handling can be framed with scrap lumber.

We chose catfish because they are readily available in our part of Alabama, and reach eating size in a summer. Various small members of the sunfish family, such as bluegill or bream, would also be suitable.

While we readily admit that our plan has no commercial possibilities, we know that we can produce, for our own table, tasty fresh fish that is uncontaminated and costs practically nothing, both considerations being highly relevant at this time.

Fish are usually efficient food producers; a one-pound fish yields approximately 10 ounces of food. Further efficiency is indicated by the fact that fish fed on commercial fish ration convert about 85 percent of their food to meat. While we are not prepared to compute the technical data about food conversion in fish on an earthworm diet, we can readily state that the fish relish earthworms, and do grow well on this food.

Spraying the water back into the tank aerates the water and at the same tie releases the ammonia produced by excretory matter in the water. Because the oxygen requirements of fish are quite high, the faster the circulation of the water, the faster the growth of the fish.

We decided to keep our equipment as simple and inexpensive as possible at the beginning, but to use the maximum stocking density advised, keeping 40 fish in a 55-gallon drum. Although inexpensive circulation pumps are available, we chose to use a METAFRAME HUSH II aquarium bubbler for oxygenation and a garden hose to siphon off water from the bottom of the barrel.

We take off 15 gallons of water per day, but as we run the wastewater onto the worm beds and adjacent garden, the cost is negligible. Although we have creek water close at hand, we were advised to use city water to avoid the introduction of undesirable algae and fungi that might be harmful to the fish. Because city water is usually quite highly chlorinated, it is necessary to draw the water in 5-gallon buckets and let it stand for a day in the sun before emptying it into the drum to replace the water siphoned off. We have seen no evidence of oxygen starvation in the fish with this method of water circulation.

The most important variable we have found is water temperature. Catfish will feed at temperatures as low as 40 or 45 degrees, but their greatest growth is achieved at 84 degrees. We noticed a decided increase in feeding activity when we painted the barrel black and moved it into full sun. Leaving the buckets of water in the sun not only speeds chlorine dissipation but warms the water as well. In areas where city water temperatures are close to the growth optimum, the chlorine can be removed by setting the hose nozzle at fine spray, and the barrel can then be filled directly from the water supply. Although summer growth is greatest, the project continues throughout the year. By judicious use of sun when possible, plus auxiliary heat when necessary, winter growth can be kept at a fairly high level.

When water temperatures are right, the fish will feed so enthusiastically that they may leap completely out of the barrel. For this reason, the top of the barrel should be covered completely with a pane of glass which will also help in keeping the water warm. Because fish feed most eagerly in late evening and early morning, we feed them at these times of the day. As with earthworms, care must be taken not to overfeed. In warm water and bright sunlight, any uneaten worms will die and decompose rapidly, giving off gases which are poisonous to the fish.

Transferring any grown animal to a confining environment produces the equivalent of cultural shock, and is followed by a period when feeding is light and growth is slow. At this time special care must be taken not to overfeed. Unless fish can be found that have been hatched and grown in a tank, small fish should be selected to stock the barrel, as their adaptation time is proportionally shorter that that of larger fish. To eliminate as much transplanting shock as possible, we use a large wooden box, lined with two layers of polyethylene sheeting and covered with an old door, to stock with fry. By the time the fry reach fingerling size, they can be transferred to the barrel as replacements are needed, and very little shock is evident. An insect lamp over an opening in the cover of the fry tank permits the small fish to eat at night while ridding the garden of night-flying pests.

Earthworms, as any angler knows, are food for fish in their natural habitat; and most fish in captivity prefer live food to the dehydrated type. Kitchen scraps make excellent food for earthworms, and even the most careful organizer will have enough refuse to feed, quite handsomely, 5,000 to 10,000 worms.

We found that growing earthworms at home is not difficult. The basic materials are easily arranged, and the earthworms’ demands are simple. All they require are a protective container, reasonable temperature control, adequate moisture, not too much food, and a light loose bedding which is never allowed to become acid.

The steel half drums are ideal worm bins as they are effective protection against the earthworms’ predators in addition to being quite inexpensive. They have the added advantage of being movable so that as cold weather approaches, the worms can be carried to an enclosed porch or basement to continue composting activity and fish food production throughout the winter.

Each half-drum will house between 4,000 and 6,000 worms. The two half-drums are utilized most effectively if they are alternated so that the worm population is allowed to build up in one, while the second supplies the fish food. The eggs that remain after the worms are removed will serve to start a new supply when the first drum is converted to feeding.

Worms will start breeding when they are about 90 days old. Each worm, possessing reproductive organs of both sexes, will produce an egg capsule per week, containing from three to 25 eggs apiece. The most economical way to establish worm bins for a home food-chain and composting operation is, to begin with capsules. Although a little more time is required initially, there will ultimately be more worms available to work with. Under the protected conditions of a worm bin, the survival rate of young worms is very high.

The type of worm selected is not important. There are two compost-bait types raised commercially — usually known as “brown-nosed worms” and “red wrigglers.” Either type may be purchased from most dealers.

The bedding for the worm bins may be any organic material that is water-absorbent and does not pack so as to exclude oxygen and impede the worms’ movement. Leaves and old straw are good, as is aged sawdust soaked in several waters for a week or so. Ground peat moss, being odorless, is ideal if the worms are to be kept inside. Soil should never be used as it contains no nutriment and is likely to pack.

It is safe to assume that earthworms can eat any kitchen scraps except citrus rings, vinegar dressings, and bones. Though they eat almost anything given them, their intake of food, and likewise the production of compost, can be increased by frequently feeding foods that are especially tasty to them. The prime consideration is to avoid overfeeding. Although worms thrive on decaying food, they should never be given more than they can consume in 24 hours.

The dangers of acidity cannot be overemphasized. It is the only real hazard in worm raising. Acid bedding frequently destroys an entire worm farm in a few weeks. To maintain accurate control over the acidity, one should use a soil test kit or a pH test strip of the type used by industrial and medical laboratories.

Tests should be made at least once a week, and the pH factor (degree of acidity) should remain between 5.5 and 6.5 on the scale. A reading of 5.0 or below means danger, and immediate steps must be taken to neutralize the bedding with an application of pure ground agricultural limestone. It is important to read the label carefully to verify that the limestone does not contain any added phosphates which also bring disaster to a worm bed. 

The drums should be located in an area protected from temperature extremes. Optimum temperatures for feeding and growth are between 60 and 70 degrees, but worms will thrive in most summer climates if the beds are well shaded and the bedding is kept loose. During the summer months, the bedding must be sprinkled daily, but it should never grow soggy. The glass tops on the half drums serve to conserve moisture, but they will not prevent crawling. Worms have a tendency to roam at night during damp or rainy weather unless preventive measures are taken. A small light over the bed is an effective deterrent to their wanderings, while an equally effective measure is to cut a remnant of carpet to fit the drum exactly and lay this on top of the bedding.

The table scrap-earthworm-catfish food chain, even from its inception, was never intended to evolve into a money-making project. It was simply an effort toward a better way of life through cooperation with the forces of nature; and in this respect, our project has been a complete success in more than one way.

First of all, we have a regular supply of fresh fish at minimal cost. A seven-ounce catfish fingerling grows to 25 ounces in a summer, thus producing a pound of food in four months. In the second place, we have netted ample compost for our vegetable garden, thereby further ensuring a low-cost and nutritive food supply. In addition, and perhaps this is the greatest benefit of all, we have the satisfaction of working with growing things and the gratification of knowing that we have not wasted the earth’s resources. We have made an elementary biologic principle work in our own backyard.

IF YOU’RE THINKING OF RAISING CATFISH

The fish were channel catfish.

Our fish were not fed exclusively on earthworms in that we started them on commercial catfish food. Because it is very difficult to teach pond-grown fish to eat in confinement, we offered them exactly the same food they had been eating in the pond. We continued these rations for about four weeks before their response was sufficiently enthusiastic to risk changing food. Then the earthworms were introduced gradually — a few at a time — until the fish accepted them.

Some of the fish recognized the worms as food immediately, and within a week the water literally boiled when the worms were thrown in. We wondered, then, if they might not have started eating more readily if we had used the worms initially.

The weight of fish: We don’t have any figures at all on the weight of the fish we started with, and we didn’t weigh any before we ate them. As we stated in the article, we began with 40 fish — fingerling size. Although we arrived at this number on the basis of Auburn’s ratio of water as estimated by the fish farmer from whom we got the fingerlings. He didn’t weigh the fish and we don’t remember what that estimated weight was. We didn’t know this thing was going to work.

Earthworms: Again we have no figures on pounds of worms used. For reasons of ethics (we advertise in OGF), we didn’t mention in the article that we are in the worm business. Since we have so many worms around, it just didn’t occur to us to keep records of how many we used. We simply tossed the worms into the barrel until the fish stopped eating. We fed once a day, but we don’t think that all of the fish ate at every feeding. I would estimate an average of 75-100 worms per day. The worms were small, not weighing more than an ounce per hundred. We were careful not to feed breeders to the fish.

Table scraps: We have been feeding table scraps to earthworms for a number of years; and to date, we have not weighed a single scrap. We can, however, offer fairly precise figures on this step. Earthworms are reputed to produce their own weight in compost daily; but our experience has not indicated that they really do. A thousand worms weigh 13 or 14 ounces, but daily feeding per thousand does not approach that weight. We usually keep a container of around 2,000 composting worms in the kitchen, and I give them a couple of tablespoons of selected (that is to say, soft and mushy) scraps each day. In liquid measure this amount would be only two ounces.

It never occurred to us that a nutritional deficiency might develop in fish fed only on earthworms. I doubt that either of us would have recognized malnutrition if it had occurred. As we don’t have backgrounds in biochemistry, we are not in a position to make any statements concerning the nutritive value, qualitative or quantitative, of earthworms. We did definitely notice a considerable increase in feeding activity when we started giving worms.

In fact, we ate our first fish — seven of them — when they were only ten inches long because they jumped out of the barrel, and we didn’t want to put them back for fear they had been injured. We feed our tropical fish (Red Oscars) earthworms also, but we can’t continue the diet for more than two months at a time because the fish get so lively and eager for food that they leap out of the aquarium whenever we lift the cover for feeding. I would say we are inclined to agree that earthworms are a near-perfect fish food.

The text and illustrations of this article are from Organic Gardening and Farming; January 1972 The new series of reader research projects starts with an exciting plan to turn grass clippings into organic fish.

Dr. John H. Todd with Dr. William 0. McLarney, Director of Aquaculture Director of Aquaculture Studies for the New Alchemy Institute

OVER THE PAST FOUR MONTHS in the series “Shaping an Organic America” I have dealt with the urgent need to create a science and biotechnology which will permit revitalization of the countryside along organic and ecological principles.

It is my belief that if such a science is developed and its findings put into practice, an ecological crisis of saddening dimensions can be averted. I have also pointed out that there is no guarantee for the development of a truly ecological science by the scientific community alone.

Most scientists simply are not trying to set examples for the future by living and working with the earth. Because of this, the recommendation was made that the science for the organic method should marshal the participation of many, many people from all walks of life arid particularly you who are already working with the land.

If this were to happen, then a true restoration of the countryside might be possible. I know that this is a tall order and no doubt the concept will be scoffed at by many scientists. Yet, my confidence in the whole idea of the Readers’ Research Program has been bolstered by the letters I have received following my article in the November issue of OGF.

Several really ingenious and even brilliant ideas have been presented by a number of people. (In a future issue I would like to describe some of these exciting plans and discoveries which are not directly associated with the experiments outlined in this column.)

In the entire history of man, there has probably never been a period quite like now when so many people feel a sense of despair and helplessness towards the future. I think this can be changed if enough people are able to see even the slightest possibility of embarking upon a personal course of action which will truly benefit the planet as well as themselves.

Organic gardening, farming and homesteading are among the most positive steps that can be taken in this direction. Involving ourselves in creating a science for tomorrow is a commitment upon which so much will depend. This month inaugurates the Readers’ Research Program and for many of you working with us, it will be a way of beginning, in the words
of Bob Rodale, “1972 as the Year for Organic Action.”

Introducing the Readers’ Research Program

New Alchemy Institute scientists, with the support and collaboration of the editors of ORGANIC GARDENING

And Farming magazine, will be working with you to organize a widespread, continuing research program to investigate many of the important organic concepts. As gardeners and homesteaders you will have the opportunity this year to become involved in any one of at least three scientific projects.

Besides the Back Yard Fish Farm research which is described in this article, the second project will involve a country-wide search for the most pest-resistant varieties of vegetables. At the present, this essential information is not widely available to the organic gardener.

The third Readers’ Research project planed for 1972 will investigate ecological design in agriculture. Specifically, we will compare complex interplantings of vegetables in home gardens with single or monocrop plantings. Soil fertility, resistance to pests and a number of other variables will be measured and the differences between the two approaches will be analyzed.

I would like to begin by describing the way in which the Readers’ Research Program will be organized. Each of the research projects will be outlined in these pages. After you have read the articles outlining the projects, if you are seriously interested in working with us on a specific experiment, please inform us of your intent to become involved. The address is: The New Alchemy Institute, Box 432, Woods Hole, Mass. 02543. After you contact us we will send further instructions on how to set up the experiments, what equipment you will need, where to get it, and how much it will cost.

There is one point I would like to emphasize at this time. If the research program is going to succeed and be an important source of information, please do not ask us for project instruction booklets unless you honestly intend to carry out experiments with us, and have the space and facilities to do so. The booklets cost money, and replying to casual inquiries takes up valuable time. Since we are operating this program on a relatively low budget, the time and money you save us will give us a greater opportunity to work toward the success of the program. All the information you need to make a decision about your participation can be made on the basis of what you read in this column. The booklets will only add the “how-to” details and outline some of the potential pitfalls that the investigator needs to know about.

The organization of the first project, the Back Yard Fish Farm, will be slightly different. It is possible that the number of people who would like to become involved will exceed the supply of brood stock which we have available. Thus, we will have to limit the study to match the supply of fish.

The procedure for the Back Yard Fish Farm will be as follows: First, if you are seriously planning to get involved, contact us. Then, just prior to constructing the dome and installing the pool, you must contact us again to see if the fish are available. If we say yes, fish will be reserved for you. When the fish farm is built and a picture of it sent to us, we will ship the fish for the experiment.

Becoming involved in a research program may also provide a bonus that you may not have counted on; you will get to know the nearest organic gardener-scientist working on the same project. If at all possible, we will try and send you the address of the nearest participant, so that you can work together if you wish.

As the growing season proceeds you will continue to collect scientific data. At the end of the season your results will be sent to us for tabulation and be included with the findings of other investigators. Finally, we will describe the results in these pages and in research publications. Within a few years we will be able to make recommendations to you that have a large and meaningful body of knowledge to back them up. It is just possible that the Readers’ Research Program will help create the wisdom that will guide those of us who are working with the land.

The Back Yard Fish Farm, A Revolutionary New Way To Raise Foods at Home

Dr. William 0. McLarney and I are working together to organize the Back Yard Fish Farm research. The project involves a totally revolutionary concept in agriculture. If it should prove successful, fish farming, on a small scale at least, could become a common practice throughout the country.

We are proposing that you raise fish in a small pool inside a geodesic dome using intensive culture methods. You will create tiny fish farms which are organic and capable of producing foods of excellent quality. If you have ever enjoyed keeping an aquarium of tropical fishes, then I think you will receive the same pleasure as well as a food crop from the Back Yard Fish Farm.

In the November issue of OGF, I described some of the thinking and theoretical concepts which went into our Back Yard Fish Farm prototype. I also outlined the reasons for choosing herbivorous fishes from the tropics and using the dome to create a suitable climate. I think it would be wise to reread that article, as space limitations prevent my repeating it. This research project will use the same methods and fish (tilapia) as we did in our prototype.

What I didn’t point out in the November article is the necessity for developing organic methods in aquaculture. It has become clear to us that organic fish products are desperately needed in this country. The area of Cape Cod in which Bill McLamey and I live is dotted by tiny lakes, many of which provide good fishing. Bill, an ardent fisherman, can be seen often casting for pickerel, perch or bluegills.

His harvest is an important source of food for a number of us. Since fish are one of the most complete, health-giving foods, we usually jump at the chance to eat them — or at least did, until a pesticide-chemist friend examined our fish.

The little pond in the woods, far away from industry and agriculture, is contaminated. The perch we were eating had up to 40 parts per million of DDT in their fatty tissues. This is far above the allowable limit for foods. We already knew that many marine fishes are contaminated with a variety of harmful substances, but the pond was the last straw. We had to start figuring out ways to grow fish organically and cheaply and we had to do it soon.

Philosophically, we were committed to small-scale intensive systems, based upon ecological and organic principles. If the fish were to be relatively poison-free, their diet would have to consist of aquatic plants and algae; this would shorten the food chain and make the system more productive while less prone to accumulating harmful substances in the fish. The prototype we developed will act as a model for the initial OGF research project.

How To Do It

The first task of the experimenters in the Back Yard Fish Farm research will be to build an inexpensive geodesic dome which will house the pool for raising the tilapia. Tilapia are excellent and much revered tropical fish which will primarily eat the algae you grow right inside the pool.

In order for the tilapia to grow to an edible size, which is about one-half pound, a growing season that’s at least six-months long in water that is normally well above 70 degrees F. will be required. The dome provides these high temperatures by trapping the heat from the sun, which is stored in the pool and transformed into algae growth. The fish will die if the temperature drops much below 60 degrees F. Their vulnerability to cold is one of the reasons we chose this

fish. If some careless person ever takes them out of the dome and puts them in a local stream or lake they will not survive the winter to upset the natural ecosystems. This is not true for the Imperial Valley in California, parts of southern Florida and southern Texas. Although tilapia are now found wild in these areas, we do not plan to aggravate the problem of exotics by conducting experiments in these regions where they can survive outside the dome.

The dome is a very effective heat trap and the pool is quite an efficient heat retainer. At the time of this writing, which is late October, the water temperature in our prototype Tilapia-Dome is still in the 60s even though the outside temperatures have been dropping near freezing at night. With the addition of a little bit of heat, we have been able to push the temperatures up into the 70s during the cool days of fall. With design improvements in the dome, we think that even in our climate, the addition of heat will not be necessary in the future.

Building the Dome

Building a geodesic dome is relatively easy and inexpensive. You should plan on two or three days to complete the task. Some of you living in the more southerly regions of the country will be able to build them for less than $50. More sophisticated structures, incorporating a double skin of clear greenhouse vinyl with an air layer in between to prevent heat loss, will last for a number of years but could run as high as $200 for materials.

Feeding time in the tilapia dome. Their main diet will be the algae which grow in the pool, but it should be enhanced with small amounts of insect larvae.

Some of you living in the more southerly regions of the country will be able to build them for less than $50. More sophisticated structures, incorporating a double skin of clear greenhouse vinyl with an air layer in between to prevent heat loss, will last for a number of years but could run as high as $200 for materials.

Our prototype was a dome 18 feet in diameter, although we wished that it had been larger. One problem was that we couldn’t move around the 15-by-10-foot pool inside. This was annoying as I had wanted to start some plants growing inside, and to do more insect-culturing research to provide new kinds of supplemental foods for the fish. The optimal size for domes to be used in the Back Yard Fish Farm would be 25 feet in diameter.

This size should provide freedom to work inside while allowing a greenhouse area. All of our future research domes will be of the larger size. Costs begin to shoot up drastically when the diameter exceeds 25 feet. Our dome was built by Multi Fassett and Marsha Zilles of Earth House in Cambridge. The plans they used and strongly recommend for the Back Yard Fish Farm research can be obtained from Popular Science magazine, 355 Lexington

Avenue, New York, N.Y. 10017. (Ask for the Sun-Dome Plans.) The plans and instructions cost $5 and include a license to build it from the inventor, Buckminster Fuller. You should also read Knight Starr’s OGF article in the September 1971 issue on the geodesic greenhouse. Although this dome is too small for the fish experiments, he does provide a lot of valuable information. If any of you have access to a cheap supply of window glass, you may be able to build an experimental dome which will last for many years.

The Pool

The pool can be any type of children’s swimming pool, which varies in price from about $40 to $100. We used a 15-by-10-by-4-foot-deep, almost rectangular pool with a 3,400-gallon capacity. We assumed that this shape would be more conducive to breeding fish, but this original supposition was not correct. A 12-to-14-foot-diameter pool, 3 feet deep would do just as well and cost much less. The
volume of this pool would be close to that of the prototype since we only filled ours to a depth of three feet.

There is an alternative way of constructing a pool which would be less expensive: digging a pond in the ground, about three or four feet deep and 12 to 15 feet in diameter. Since we haven’t tried this method, we don’t know how well it will work. If your soil is heavy and contains clay, lining the pool to prevent water seepage will not be needed. One problem that we can foresee with the pond-pool is the loss of heat from the water into the surrounding soils. This might be minimized by the use of an inexpensive liner combined with a good insulating material.

Fish for the Back Yard Fish Farm

Tilapia, a tropical fish native to Africa and the Near East, will be used in the experiment. They eat algae, the microscopic plants that color lakes green. This coloration is especially prevalent in the summer months. Because it is possible to grow algae in huge amounts and at almost no cost, algae-eating fish can be raised quite cheaply.

Each of the experimenters participating in the project will receive one pair of tilapia parents from us. The only cost to you will be shipping and handling fees, which might run as high as $25, depending on where you live. However, if they survive and breed, this will be the only investment in tilapia you will ever have to make. Once established, the parents will be capable of producing thousands of young per year. This will supply you with plenty of offspring and you will be able to pass them on to any friends who may be interested in starting their own Back Yard Fish Farm.

Place the adults you receive in the dome pond. As soon as the temperature climbs to the low 80s they will start to breed and lay eggs which they care for in their mouths. Don’t panic at this stage; they are not eating their young. Tilapia are members of a group of fishes known as mouth-breeders.

After the brood is hatched and swimming freely about the pool, the parents will breed again if conditions are right. This process should continue until an optimal population density for your experimental pool is reached. If, after sampling the population, you find that there are more than 500 fish in the pool, you should pull the parents out to prevent overpopulation and stunting of the residents.

After the first year’s growing season is over, if the conditions have been favorable, you will have an excellent crop of edible fish. These can be frozen or stored live in aerated tanks for eating fresh as needed. The Malayan peoples in the Orient often store their live fish in rain barrels just outside the back door. Fish that are not of edible size can be held over the winter in warm tanks exposed to sunlight, or they can be fed to the chickens or pigs as an excellent high-protein organic feed.

The idea of feeding livestock herbivorous fishes is not as crazy as it sounds. At present, we are experimenting with growing tiny herbivorous fish, to be cropped at a small size, as a future source of organic food for poultry — but more about that in a later issue. A small number of fish should be held over the winter. That way you will have brood stock the following spring.

Food for the Fish

The main diet of the tilapia will be the algae which will grow within the pool. After the pool is filled in the spring, one-gallon samples of water from a number of local ponds should be added. This makes it possible to seed your pool with a variety of algae species.

You will also have to provide fertilization. In our prototype we suspended a small burlap bag filled with horse manure. We estimated the algae growth by scooping the water into a tall glass and examining the color. If the water looked green enough, we shook the bag every few days. When the “bloom” began to wane, we replaced the used manure with fresh. Many of you will have cow, chicken or rabbit manure which can be used instead of horse manure. The weight and source of all fertilizer used must be recorded. It is very important not to over fertilize, as too many nutrients could deprive the water of its oxygen. Be careful!

Supplemental Feeds

Thousands of years ago the Chinese found that the growth and health of plant-eating fishes is enhanced by feeding them small amounts of animal matter in the form of insect larvae. This past season we raised our fish on a variety of insect larvae including mosquitos, midges, rat-tailed maggots and house fly larvae. Each experimenter should culture one or two types of insects or earthworms. The goal should be to produce one-half pound per day of these animals. Two productive and easy insects to culture are the ordinary house fly and the midge.

If you have ever opened a garbage can that has rotten meat in it and seen the thousands of larvae or maggots crawling around, you have discovered how easy it is to raise fly larvae! Small garbage cans and a little waste meat might produce the supplemental food your fish need. Midges are cultured on trays in water fertilized with manure. The production of one pound of midges per day on a three-foot-square rearing tray has been achieved by fisheries scientists in Israel and Florida.

Apart from the algae and the insect larvae, your system should require few other food inputs. We have tied bunches of carrot tops and grasses to rafts as additional feed in the prototype Tilapia-Dome.

Collecting of Scientific Information

Intuition and common sense have played a large role in fish farming in the past. Science has hardly penetrated the domain of aquaculture. But scientific data is needed if we are to discover the best possible methods of fish farming.

It is essential that the participants in the Readers’ Research Program collect basic scientific information. At least half an hour per day should be spent caring for the Tilapia-Dome and collecting information. The first year’s data will not be very difficult to collect. We
need:

1) Temperature profiles taken twice daily, including air temperature, temperature within the dome and in the water; also, a log of weather conditions.

2) Estimates of the population in the pool made at least twice; once at the end of the month following the first appearance of young fish and once at the end of the season.

3) Measurements of fish growth taken each month from a selected sample of individuals.

4) Production calculations made at the end of the growing season by counting and weighing the total crop.

Building the geodesic dome is comparatively simple and inexpensive. It should take two or three days to complete the job. Costs can run from $50 to about $200.

5) A description of the food used (worms, insect larvae, etc.) must be given with the amount listed in pounds.

6) A description of the amount of fertilizer and the source must be given, including the length of time between changes.

Hopefully, we will be able to design a simple colorimetric test for you to estimate algae production on a weekly basis.

We do not know how successful the Back Yard Fish Farm idea will be. We have indications from the prototype that it will work. In fact, some of you may produce edible organic fish at less than 20 cents per pound (exclusive of your labor), some may even set still-water fish culture records for this country. All of you will have fun and learn a lot.

The experiment is risky . . . you could also end up with fish only large enough to feed to the chickens.

This may not make you happy, but your scientific data will tell us what went wrong. Your Tilapia-Dome can be used as a greenhouse the following winter, or if you are excited by aquaculture, you may decide to trap native fishes and fatten them in the dome in the winter. Thus, the experiment cannot really fail.

Bill McLarney wants to start a research project to find out if the dome can be used for two fish crops a year. During the winter he would like to try fattening bluegills, perch, crayfish, and clams to be harvested before the tilapia experiments begin again in the spring. The majority of us here want to use the prototype dome for growing kale, spinach, Chinese cabbage, and lettuce this winter. I suspect the cooks rather than the fisherman will win the first round.

I hope many of you will become involved in the OGF Reader’s Research Program. It could become a potent force for a saner agriculture in this country.

The Solar Greenhouse That’s Right for You (Text & illustrations for this web page came from the August 1978 issue of Organic Farming & Gardening) Here is a new gardening tool that produces fresh food when the snow flies.

by JACK RUTTLE

ALMOST ANY STRUCTURE that is built to look like a solar greenhouse will work. That is to say, the solar greenhouse concept is so right that you can ignore (or not know) the fine points of solar design and still build a house with much less need for supplemental heat than a traditional greenhouse. But once you understand a few basic solar-greenhouse design ideas, you can easily put together a greenhouse that truly lives up to the label solar, and provides remarkable efficiency.

Dave MacKinnon, Ph.D., ORGANIC GARDENING greenhouse designer, has put it all together after three years of experimenting and has created a design formula that gardeners in any climate can follow. His newest solar greenhouse, which he has built and tested in Flagstaff, Arizona, epitomizes a good solar shape. It has produced food through two winters without requiring any outside heat source. Almost all the floor space is usable for growing beds because the energy storage is on the walls. And it uses a minimum of materials because the design, insulation and heat storage are in balance and arranged to complement each other.

The best measure of a solar greenhouse is the plant-growing environment it creates. When the building is skillfully made, you will get midspring soil and air temperatures in the depths of winter on sun power alone.

Our experiences suggest that solar greenhouses can maintain that kind of environment in most parts of the country. ORGANIC GARDENING researchers have built two different greenhouses that have worked well despite unusual winter weather. The Flagstaff greenhouse performed well with much less sun than is considered normal, and the one at our Maxa-tawny, Pennsylvania, research center worked through the coldest winters in recorded meteorological history.

In December and January, we harvested enough salad greens every day for three or four people. Cold-hardy plants, all very rich in vitamins A and C, produce best. Escarole, lettuce, parsley, corn salad, chervil, chives, and other salad herbs are dependable. So are kale, chard and chicory, which grow so thin and tender in the weak winter sun that they are best in salads too. In spring and fall the harvests are bigger. Succession plantings make heat-loving plants like tomatoes and cucumbers possible far beyond their normal seasons.

Dave MacKinnon’s solar greenhouse greatly expands his crops of homegrown food. He picks salads every day through winter. Frost nips his outside garden early, so greenhouse protection has meant the first heavy-producing tomato plants he’s ever grown.

SOLAR GREENHOUSE BASICS

At the least, a solar greenhouse should have three features. One of the long walls should face due south rather than east or west. The south wall should have two layers of glazing. All the surfaces that don’t face south are insulated. But there’s a little more to it than that if the greenhouse is to live up to its solar potential. The new Flagstaff greenhouse is a perfect model.

Dave MacKinnon says the greenhouse should be about twice as long (east to west) as it is wide. Accordingly, his Flagstaff greenhouse is 20 feet by 12 feet. The two-to-one relationship offsets the effect of the shade that the opaque east and west end walls create. The building thus captures more solar energy for each square foot of growing space. If the building is made much deeper than two to one — that is, closer to a square floor plan — the heat-storage material in back is shaded too much. These proportions are recommended for greenhouses everywhere.

MacKinnon has learned another rule of thumb for sizing the energy-collecting south face properly, and has built it into the Flagstaff greenhouse. The peak should be made about as high as the building is wide (north to south). Heat-storing materials in the back of the greenhouse will then get the direct exposure to the sun they must have if the storage is to work efficiently.

The slope of the north roof is an important feature of MacKinnon’s greenhouse, though the precise angle of slope is not critical. Sunlight which enters the greenhouse and strikes the aluminum-foil-covered roof (white paint works well too) is aimed back down to the growing beds. From the outside, the interior of the greenhouse looks almost black because very little light is bouncing back out to the viewer. If designed well, solar greenhouses with reflective walls can actually deliver up to a third more light to the plants in winter. In the traditional all-glass design, much of the light passes right on out the clear north roof and wall. Angles between 60 and 75 degrees for the north roof will work well in the United States and southern Canada.

The slope of the sun-collecting south face might appear to be trickier to decide upon. The angle does affect how well the translucent face collects sunlight, but for greenhouses, it’s not as critical as when setting up a compact solar-heating unit. Actually, a wide range of angles will work equally well at any given latitude. The simplest thing to do is to add 20 degrees to your latitude. A south face with that angle will give optimum performance in January. But if that particular angle proves hard to work with, go to a slightly shallower one, and you will be favoring solar collection in spring and fall. If you use 50 degrees rather than 60, which, for example, you may figure is your ideal, you still have sacrificed very little midwinter light.

Given this leeway, other factors like convenient construction can help determine the south slope. The south face of the Flagstaff greenhouse was made steep all the way to the ground to shed snow quickly. That feature lets sunlight in sooner after storms. The Maxatawny greenhouse has a vertical glazed knee wall from which a shallow, clear roof slopes up to the peak. There is much less snow to worry about there, and this shape makes working in the front of the growing beds easier.

When it comes to putting in insulation and heat storage, however, solar greenhouses can get needlessly expensive. The key is to have sensible amounts of both. Great thicknesses of insulation can’t do away with the need for heat storage, and are wasteful. And obviously, adequate heat-storage material without a certain amount of insulation in the walls is equally wasteful. Even if you build a greenhouse that is not completely solar-reliant, using a balance of these component parts guarantees an economical building that will work well. (The information on the map indicates the proper proportion of materials, as well as recommending minimum amounts for a fully solar structure.)

HOW HEAT STORAGE AND INSULATION TEAM UP

The connection between heat-storing materials and insulation works like this. Without heat storage, solar greenhouses are something like a thermos bottle — all the energy is in the sun-warmed air. Drafts will quickly drain off the heat, because even the most tightly made building will have a fair amount of tiny cracks. Energy held within storing materials is not lost along with escaping air. The energy is released slowly as the greenhouse cools, and the building stays warm much longer.

A no-less-important effect is that heat-storage materials keep the greenhouse from overheating during the day. We quickly learned that without storage the inside temperature can soar into the 80’s or 90’s on cold, bright days. That is quite hard on a winter greenhouse crop.

With storage absorbing some of the incoming energy, the result is a milder daytime environment.

The amount of heat storage for full solar heating seems enormous at first, but is manageable in practice. Both of MacKinnon’s greenhouses use about 1,000 gallons of water stacked vertically on the rear walls. That amounts to four gallons of water for each square foot of floor space. The best method we’ve found is to use rectangular five-gallon honey cans with a rust inhibitor added to the water.

“Five-gallon honey cans make efficient heat-storage containers,” says MacKinnon. They pack the maximum amount of water into a given space.

Why do we rely so heavily on water? It is admittedly hard to work with because it tends to corrode containers and to leak. But water is about the best heat-storing material known and is cheap. The best alternative is rock (in any form from sand through concrete), but water holds about five times more heat. So water reservoirs on walls make compact heat storage that gets a good share of direct incoming sunlight.

MacKinnon favors smaller containers over 55-gallon drums for two reasons. Drums leave empty about a third of the space they occupy, because they are big and round. They also permit warmed water to gather into a few large areas, which causes both greater heat losses and poorer collection in those areas. Smaller containers keep the energy more evenly distributed. On the other hand, the large barrels are certainly worth using if they can be had cheaply. We’ve also used translucent plastic cider jugs filled with water dyed black, and have heard reports of success with beverage cans sealed with tape and stacked right-side-up.

The amount of insulation that MacKinnon judges to be practical in various regions is roughly the same as local, energy-efficient recommendations for homes. If that seems lavish for a greenhouse, remember that homes get a lot of extra heat; the greenhouse is designed to get along with none. To me, the need for plenty of insulation is a reminder that people aren’t much different from plants in their requirement for warmth, among other things. To use less insulation, however, is to need more heat storage, which demands more space and money.

Two other simple things are crucial to the success of our greenhouses. The earth below them is insulated to a little below frostline with plastic foam. And at night an insulating curtain is drawn over the clear south wall to reduce the high heat losses there.

It pays to insulate the earth below the greenhouse because the earth is a relatively poor insulator, contrary to a lot of lore.

A few inches of most common insulators match the R-value of ten to 15 feet of earth. But earth is a good heat-storing material, lying somewhere between rock and water. So insulating around the perimeter builds heat storage into the structure while stopping steady heat losses to the ground outside. We checked the advantage of doing this at the Maxa-tawny site. Six inches below the surface, the insulated soil was in the 40’s in January and in the 50’s in February, while the ground outside was frozen solid several feet deep.

The day comes when shuttering the glass or plastic face becomes practical despite the inconvenience of twice daily attention. Past a certain point, there’s no easier way to gain a few degrees inside. The south-facing glass loses a tremendous amount of heat compared to the other three-fourths of the building’s surface that is insulated. To add enough storage material to make up for what shutters can save would take too much room away from the plants.

We’ve found that a good nighttime heat barrier for the window doesn’t have to be a great insulator, but it must be durable and easy to maneuver, since it will get heavy use. More important, the material should be reflective on the inside and fitted tightly at the edges to stop air flow. A reflective material (aluminum paint or foil) will block all escaping radiant energy. Combined with an airtight seal, that seems to do plenty for me greenhouse. Beyond that, any insulating value you can build into the curtain is so much the better.

The muscle power it takes to raise and lower the heat-trapping curtain is the only non-solar energy a well-designed greenhouse needs.

Without a doubt, a thin, aluminized fabric which is operated by ropes or a pulley is the cheapest system to make and work with. The best one Dave MacKinnon tried was made of aluminum foil glued to one side of parachute fabric. That curtain lasted two years before needing repairs.

The third winter at Maxatawny we used a shutter system that could hardly be bettered for stopping heat. Panels of one-inch urethane foam, aluminized on one side, were held in place with wooden battens. We kept them in an air-lock entrance room that doubled for storing tools and gardening supplies. The only drawback to the foam is that it is expensive. Any exposed foam surfaces should be painted to waterproof the material against condensation that accumulates on the glazing.

Those are the basics of a solar greenhouse: the sun-catching design, strategically placed insulation, and heat storage. Together they make a cool-weather garden possible even in Northern states. In ours, the air inside has averaged 42 degrees higher than outside and between 45 and 55 degrees F. in the soil throughout the winter. Many vegetables will thrive in that temperature range.

VEGETABLE GROWING IN THE SOLAR GREENHOUSE

There’s a lot to be learned about cool greenhouse vegetable culture. The most important trick we’ve discovered is using the right growing container. Traditional greenhouse wisdom recommends pots on waist-high benches — easy to reach and easy to isolate diseases and pests. But continuous temperature recordings in the soil pots showed that the temperature in the root zone changed right along with the air temperature because the exposed surface of a pot is so large. There were large swings every day, extremes that plant roots aren’t used to. So we switched to two large beds 18 inches deep that cover the greenhouse floor. They held the root zone to a 10-degree daily change which is natural and also made a greater heat-storing mass.

Beds have many other advantages. Roots have more room to forage for water and nutrients. The environment becomes a better one for natural predators like spiders. Because the soil in beds holds a large amount of organic matter, they also become an important source of carbon dioxide. Plants in a sunny, airtight greenhouse can use up all the available carbon dioxide in a few hours.

Nothing like these greenhouses is available for sale yet, but several years from now you will start to see them. The big greenhouse manufacturers are redesigning their products exactly along these lines. They will probably be expensive. But a home-built, sun-heated greenhouse like ours

can be constructed now for less than the finest energy-wasting glass house, and will be tailored to match your local climate.

In the far North, where solar greenhouses will be the most expensive to build, they will yield the greatest expansion of the gardening season. Even in southerly Flagstaff, Dave MacKin-non reports that his solar greenhouse has made possible his first really good tomato crops, so dry and short is the growing season there.

Properly made and maintained, a solar greenhouse should outlast its builder. The materials are all durable or renewable.

House-attached greenhouses are even cheaper to build. As you plan your solar greenhouse, you should think first of this kind for many reasons. Attached greenhouses have about a third less surface area for the same floor space as a freestanding one. Thus construction costs are lower, and less heat is lost at night. Attached solar greenhouses are the most efficient hot-air solar collectors known. High and low vents that open into the home through the common wall exchange solar-heated greenhouse air for cool air at floor level from the house. At night, the house can return some of the heat to the greenhouse. All the design principles for solar greenhouses apply to the attached greenhouse, except they may need less heat storage. The only requirement is a suitable spot facing south that is unshaded in winter.

Looking only at the money, it’s obvious that a durable solar greenhouse, attached or freestanding, will repay its cost. Compared to conventional all-glass models the fuel savings alone will pay for its construction in three to four years in the North. And they make you independent of an unhealthy agriculture and the transportation system it depends upon for fresh vegetables to tide you through winter. That’s why we recommend so strongly that you build one if you can.