BUILD YOUR OWN ECOSYSTEM

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The inside wall of the fish tank was also made of cement blocks, with every hole filled with concrete, and rebar placed at about 2-1/2-foot intervals to provide the strength needed to withstand water pressure. Please note, however, that this technique was a big mistake and is not recommended. When the time came to fill the tank, it leaked like the proverbial sieve. There were just too many tiny holes for the water to run through! Only after plastering the inner surface with a stucco containing particles of fiberglass (sold under the trade name of Bloc-bond) and then painting a quarter-inch layer of hot tar on the sides and bottom did we finally stop the seepage. It would be much better to use slip forms and construct a tank with solid concrete walls.

The main support for the roof framing was a 25-foot section of pine tree which we brought down from a nearby national forest. Smaller pine poles and rough-cut 1 X 4 lumber complete the framework which supports the Filon "windows". (Filon is a fiberglass product designed especially for greenhouses. Our project took three 4' X 24' rolls, which I purchased through the Sears catalog at a total cost of about $90.00.)

Ventilator flaps were provided for use in summer, when the interior heat is expected to soar well over 100° F. We finished the basic structure in mid-October and even then got inside midday readings of 104° F. Such high temperatures, of course, are not desirable and we were glad to see the thermometer drop back down into the high 80's when the vent flaps were all opened.

Winter weather put a stop to further construction for a while, but—with the greenhouse itself completed—we decided to put in some vegetables and see how they would do on their own without any auxiliary source of heat. The tomatoes and squash both lasted well into December before I took pity on them and brought them into the house. Even after that, the radishes, lettuce, spinach and cabbage held their own . . . despite inside nocturnal temperatures as low as 22° F. I have no explanation for this other than that they just did not freeze. On several mornings I entered the greenhouse to find the plants' leaves almost black . . . a sure sign of frostbite. Then, by noon, they'd all have recovered and—if they didn't set any spectacular growth records—they at least stayed alive. As a straight growhole, I think our dugout can be considered a modest success.

The accompanying chart shows the outside, inside and fish tank low temperatures for the month of January 1974. Notice that outside readings fluctuated between 10° below zero (our low for the winter) and 27° above . . . a range of 37 degrees. On the night of January 3, the outdoor temperature went down to 5° below zero while the interior showed a balmy 34° (two degrees above the freezing point of water). I attribute this result to the 10 inches of insulating snow which covered the greenhouse. Nevertheless, I became worried that the weight of such an accumulation might damage the structure and shoveled it all off . . . only to have about three inches fall an hour later. Apparently even the thinner layer insulated the shelter fairly well, because that night—when the outside temperature plunged to 10° below—the coldest it got inside was 28° above. Walking into the growhole the next morning was like entering a heated room.

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