JARS 42n3 - Fun With A Small Greenhouse

Fun With A Small Greenhouse
Martha Prince
Locust Valley, New York

Originally printed in the New York Chapter newsletter. Revised by the author for Journal publication.

On an icy winter day, when it is gloomy and dark outside in the garden, we may push open our greenhouse door and find fluffy pink blossoms on one of the camellias. Dainty little yellow Primula kewensis may be opening its buds. We can tug gently on the rhododendron cuttings, lined up in their flats, to see if they have rooted properly. Our greenhouse is small, but it is wonderful fun to have.
We bought our greenhouse about ten years ago. It is only eight feet by twelve, a "lean-to" set against the house. We chose a so-called "solar model" (from Four Seasons) because the design seemed good and it was comparatively inexpensive. This was a "do-it-yourself" project; the pieces arrived in large flat cardboard boxes and had to be put up like some oversized Erector set. My husband, Jordan, is good at this sort of puzzle and I'm a willing helper - but I would not recommend such a project for everyone. It proved to be a major construction job!

Drawing by Martha Prince

Step one was to excavate a neat 8' x 12'rectangle, to a depth of 18 inches. There is a footing of treated redwood boards, half in ground and half above. In the corners are aluminum posts set on flagstones. After laying in the air-ducts (which I will explain in a minute), poor Jordan had to haul five heavy yards of gravel, to fill in the whole space. The instruction book labels this the Heat Storage Bed.
The frame went up next. It is of aluminum with a baked-on bronze finish; putting it up was a two-man job. At least I'm good at holding things and I could be actively helpful in getting the walls into place.
The wall panels are of plastic (to quote the instruction book, "a high UV stabilized polycarbon plastic with 45% better insulation than single layer glass"). Lexan is the trade name. It is made by General Electric. One big virtue is that it is double-wall and as it was extruded as one piece it cannot come apart. The claim is that it is shatterproof. I believe it; small tree branches have crashed down with no ill effects. The panels are translucent rather than clear (80% transmission of light), so the light is somewhat diffused.
Attachment to the frame is with clips, an easy procedure - for the flat sections. The curves were a struggle! For these I pulled and tugged as hard as I could while Jordan clipped. On one end we used a single clear panel, so we could peek in, and the door is also clear.
Inside, the first thing installed was an inexpensive stainless steel sink. Jordan turned out to be a good plumber, too. Aluminum bench supports were part of the pre-fab package, and for the work surface he chose 1" x 6" redwood planks set with space between. In the diagram you can see the arrangement.

glasshouse interior
Drawing by Martha Prince

I'd now better explain the Climate Control System. The air ducts I mentioned (laid in the gravel at the bottom of the Heat Storage Bed) are perforated P.V.C. pipes centered under the benches. Connecting ducts go up to the peak, then along the top next to the house. These utilitarian objects we painted bright orange, to add a bit of cheer. On the floor in one corner is a centrifugal fan in a box, called the Air Control Chamber in the book (sounds more important!). This fan is always on. There is also an automatic - louver exhaust fan at the peak. Two louvered ventilators are set low in the greenhouse walls, one at an end and one in the middle. One of these has an automatic flap valve, in front of a manually set jalousie.
The idea behind all of this is that in the winter heat from the sun is stored in the gravel during the day, then released at night. In summer, the excess heat is exhausted by the top fan (set to go on at 90 degrees). The cooler gravel serves to moderate the air temperature, too. The fan in the Air Control Chamber works constantly to pull air from the top down into the gravel bed. We find that this circulation is very important, not just for temperature but to provide the air movement necessary to avoid fungus problems.
This solar arrangement, helpful as it is, is not adequate in the winter. We installed an electric heater (Titan 220, volt 13,000 BTU) with a thermostat set for 42 degrees. For summer we have a roll-down shade of 55% polypropylene mesh screening, to modify the sunlight.
Temperature control isn't the only necessity, of course. There's water. What we have is a very adjustable misting system which my versatile husband also set up. For "general environment" he uses only three mist heads; these spray for ten seconds every five minutes for an hour in the morning, then again for the same time in the afternoon. This is our minimum usage. There are a total of 8 mist heads, in two rows, so we can use as many as necessary. For instance, when a lot of rhododendron and azalea cuttings are being rooted the whole mist system may be in action and for longer times.
Another necessity is artificial light. We have three double four-foot fluorescent light fixtures, which can be raised, lowered, or removed. These are mostly used for pushing deciduous azalea cuttings. Speaking of deciduous azaleas, bottom heat is also needed when pushing these. To provide that, there are two heating mats, size 2' x 5'.
What do we grow in this little greenhouse? There are no full-time plant residents. The occupants change from season to season and from year to year. We do not start seedlings here (for this we use a Lofthouse-modified Wardian Case in our garage). Seedlings move to the greenhouse once they are pricked out in the spring. We do all our cuttings here under mist - elepidote rhododendrons in the fall and winter, softwood cuttings of lepidotes and deciduous azaleas in late spring or early summer. Both cuttings and seedlings are banished to the outdoors at the proper time (cold frame or liner bed, depending on size and maturity). Some fragile-looking little ones may be held over a second winter.
We have eight Camellia japonica plants, three to four feet tall, which spend the winter clustered on the far bench, blooming for us there. These summer outdoors, in a sort of protective wire cage we call "the rabbit house". Two large hanging baskets of fuchsias are in the greenhouse from October to late May, before taking up residence on the terrace. There also is a tub of tuberous begonias and various other begonias in hanging baskets. We are planning to add a few Vireyas.
We too often succumb to curiosity and temptation, such as growing "impossible" seeds from R.H.S. After admiring the yellow-flowering (and prickly) gorse in England we just had to grow some! But, what does one do with ferociously wild bushes which are too tender for Long Island? Eventually some of our greenhouse experiments have to be tossed out. At least the greenhouse lets us try.
A much-appreciated use for the greenhouse is as a plant hospital. Several years ago I had a lovely white African violet on the kitchen window-sill. It developed a seemingly incurable case of tuberculosis, or something, and went to the greenhouse for a cure. Now it is back in the kitchen with its pink and lavender friends, blooming happily. Other houseplants go down, too, for rest and rehabilitation. At the moment there are some recuperating philodendrons.
A special pleasure is to have a few earlier blooms of a favorite garden flower. Last year we especially delighted in the lovely blue of Aquilegia alpina , out of season. For us, the little greenhouse works just beautifully! It is sufficiently "automated" to accommodate rather disorganized gardeners, which we are. We procrastinate, we forget, we have lazy spells. Jordan suggested that I tell you this: "A greenhouse is like Scotch tape, air-conditioning, or Saran wrap. Once you have it you can't do without it."
I am writing this in January. Early this morning Jordan cut two fresh camellia blossoms for the breakfast table. One is the dainty pink 'Debutante' and the other a frilly white Triphosa'. What could make a brighter winter morning?