eGarden © 2004 Ed Mues

From The Garden of Ed. Submitted for publication in The Towne Crier on December 29, 2004

My Catskill Solar Heated Greenhouse.

This time of the year is inspiring, especially, I think, because of the "winter light". I seem to recall a Bergman film of the same title. I remember how cold everything was, the landscape and the characters, both longing for warmth and light (enlightenment?). The short days and long nights, the seasonal affective disorder in some of us, the out of ordinary responses we get to certain prompts, these all seem to point to the approaching of the winter solstice. I'm sure there are magical, mystical, someday to be revealed secrets of what happens to so many of us at this time of the year, as well as in the second half of June, on the longest day and shortest night of our year. (Makes me wonder how significant the moon's role is, ie. lunacy, etc.)

I am enlivened so much by the arrival of the winter solstice. It is my wife, Diane's birthday, and it is also the day my solar-heated greenhouse turns around in its function, in a couple of ways. I know that sounds cryptic, but here it is in a nutshell. My greenhouse requires me to supply it with supplemental heat, and in exchange it supplies me with supplemental heat. In only this way could it reverse its function. More about this in a bit, except to let you know it's a win both ways.

My greenhouse is partially underground (2' below grade). It was designed to absorb and store heat for use when needed, and to produce horticultural product. I do not use it for food production, except some herbs. I've been chastised about this more than once from a few friends. I've chosen instead to grow exotic and unusual tropical plants.

There are advantages to greenhouse production, and disadvantages. A greenhouse in enclosed and, therefore, more manageable than a garden; its environment is controllable and more intensive. Plants tend to grow more rapidly, and, so too for pests and diseases. I'll revisit this shortly.

In order for plants to grow well, adequate light, proper temperature range, water, oxygen, carbon dioxide and nutrients all need to be present at the right times and available in the correct amount. Any lacking element in this equation is often referred to as a "limiting factor". Successful greenhouse design and operation takes into account the basic biological processes of plants and the ways in which limiting factors affect plant growth.

A well insulated foundation allows the floor to serve as thermal storage, as well as other storage media attached to it (in my case water and masonry). Without proper insulation, the greenhouse won't serve as an adequate heat sink and therefore won't store and release heat as it's needed -- too much will escape to the outside environment. Any exposed unglazed surface should be well insulated, as is the ceiling of my greenhouse. Any and all glazing should face as close to south as possible and be coverable with insulating shades or shutters when the sun sets to prevent loss of valuable heat.

Storage of thermal energy can best be accomplished by using water since it is virtually free and can store the most energy per unit volume, nearly three times that of rock or masonry. Some high tech chemicals called phase change materials are more efficient, but very pricey.

I said I used water for my collectors of thermal energy. I have 31 fifty-five gallon plastic drums filled with water and laid out horizontally the entire length of the greenhouse. They are behind vertical, double glazed thermal glass windows. The drums are painted flat black. Weighing at least 450 pounds each, they are permanent fixtures and lie beneath my growing benches providing bottom heat to my growing area. Of course, gallon milk containers or 2 liter bottles could be used, but a lot of bottles would be needed. Oh, by the way, I said my windows were vertical. That's so they can allow maximum heat gain fall to spring when the sun is lower in the southern sky, when the heat is most needed.

For additional thermal storage, my floor and rear wall of concrete assist. Up to the "sun line", as I call it, that area of the back wall struck by direct sunlight on Dec. 21st, the years shortest day when the sun is lowest in the sky, it is painted flat black. The remainder of the wall and the ceiling is painted white which reflects and diffuses light helping to brighten otherwise somewhat shaded or darker areas.

On cold winter days when the sun is shining, the air temperature inside the greenhouse can easily exceed 85 degrees F.. Snow on the ground increases the light and temperature even more. To hold temperatures to within reasonable swings, once the sun is no longer striking the glazing, I lower, with the assistance of pulleys and cords, the shades made of double layered mylar. This locks in most of the heat gained during a sunny day. The shades are raised again in the morning.

This is only my second solar greenhouse, but it has features that enhances the whole equation of growing at home with an attached greenhouse. At each end of the rear wall near the ceiling (heat rises, remember) are 8" insulated ducts (plenums) with a small fan. These fans move the greenhouse air up to and through the living quarters above. The fans are on rheostats and allow excess humidified greenhouse heated air to move upstairs and supplement the residential heating (wood) when the sun is shining. And, vice versa. That is, when it's cloudy or raining or snowing, and the greenhouse temps are cool, the warm heated air from the living area upstairs is exchanged with the greenhouse air and modulates the temperatures there. It works superbly. I remember back in the 70s reading about this in the Mother Earth News. I still have "The Almanac" and "The Handbook of Homemade Power" and loads of the early magazines. It is here that Diane's birthday and the winter solstice comes in. As the days begin to lengthen, the energy requirements of the greenhouse begin to diminish and a reversal begin to take place. More heat is supplied to the living quarters.

I don't use my greenhouse for growing in the summer, except for certain exotic plants in my collection that prefer heat and more indirect light. most of my plants come outside to the deck above. Much of it is covered (diffused light from translucent and opaque fiberglas roof panels). Here they summer admirably with excellent air circulation and the same moderate swings in air temperature, admittedly on the warmer side. A note about temperature swings: most plants, especially semi-tropicals and tropicals which covers most houseplants, thrive with such changes in temperature which stimulate abundant new growth and bud set.

Back inside the greenhouse, a mention about pests and diseases was promised. Before my plants return to the greenhouse a few things take place. First, the entire greenhouse is cleaned with a 10% bleach/water solution. It is shut tight with everything closed for a few weeks or more. Very high temperatures kill just about everything but a few of the hardiest spider beneficials. Before going back in, in the fall, my plants are carefully inspected for insects and signs of disease. Any requiring treatment are cared for accordingly. Not introducing pests is most of the battle.

Some of the more troublesome pests in greenhouses are fungus related. Watering should take place in good weather, early in the day, with minimal wetting of foliage. I use large flexible bottles with squeeze type tops like on dish detergent. I can aim the water stream right at the soil surface and not wet any leaves. To further reduce the chance of fungi problems, I increase the movement of air especially in corners where air drainage is poor. I use three fans that maintain a gentle movement of air throughout the greenhouse. I keep them going on the low setting and this costs only pennies a day.

Of the major pests I encounter, the most common are spider mites and white flies. Yellow sticky cards monitor white fly populations and often are sufficient to control their numbers. A strip or two of fly paper works well, too. If either becomes a problem, I find insecticidal soap very effective in controlling both of these pests as well as the occasional aphid that survived from outside.

It is difficult in a limited space to tell all about any solar greenhouse, or more correctly, sunspace. There are shelves of books on the subject. If you have any questions, feel free to contact me.

I must mention a bit about winter vegetable production. To grow winter vegetable without supplemental heat and light, choose hardy varieties to get established in the fall so they will approach maturity as the coldest weather sets in. This will guarantee you bountiful supplies of any of the following : chard, kale, parsley, Chinese greens, leaf lettuce, endive, mustard greens, beet greens, green and sweet onions, Brussels sprouts, collard greens and chicory.

The spring greenhouse is characterized by increasing light (day length) and higher temps. Squash, carrots, peas and beans can be started, and, seedlings for the outside garden will usually be given high priority.

A friend has asked me more than once why I don't grow tomatoes in my winter greenhouse. To anyone else entertaining the same question, the answer is twofold. Tomatoes are a long day plant that need maximum foliage development. Also, on the few I've brought inside for some winter production, some whitefly eggs or larvae slipped in, too. One of their favorites is tomato plants, and, it's not worth the risk to me and my other plants.

Once you grow things year round, you'll probably come to a new appreciation --- one that farmers and horticulturists came to a long time ago: not only is photosynthesis the most critical of plant functions, but, maybe, it's the most important chemical reaction taking place on the planet! It's about our air supply, our fuel supply, our food supply, and so on, and on ... Successful growing to all.

From The Garden of Ed. Submitted for publication in The Towne Crier on December 29, 2004

Page Up