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Growing Orchids in a Window Greenhouse
- Originally published in the March 1981 American Orchid Society BULLETIN
The exterior of the window greenhouse,
taken in October when shading covers
part of the glass.
FOR MANY YEARS we grew a very small collection of orchids on the windowsills of whatever house or apartment we happened to be living in. Our first orchid plant, Paphiopedilum insigne, which we bought more than twenty years ago from a large, commercial grower of cut flowers, is still with us, now in the form of several, good-sized plants. Two years ago, after some unexpected successes in windowsill growing (we had found to our surprise that mottled-leaved paphs grew for us just as well as the plain-leaved ones), we decided to install a "window greenhouse" in order to enlarge our collection and provide better growing conditions. (A window greenhouse is something like a bay window with glass sides and a glass roof; "greenhouse window" would probably be a more appropriate name.)
We ordered the largest window greenhouse available to us, the selection in Canada being limited, and installed it on the outside of a south-facing window in our living room. In order to accommodate it, we enlarged the window opening at one side and at the bottom; the opening now measures 48 inches by 58 inches and the greenhouse window projects 16 inches from the house. It contains two metal mesh shelves, supported in the center by a metal rod which rests in the tray which forms the base of the window. The window greenhouse arrived with only a metal tray as its base. When we had it installed we had a wooden box constructed underneath this, filled with fiberglass insulation, since we felt that this was more realistic for our winter conditions. Since the metal tray leaked, we had a heavy plastic one made to fit inside it. At the same time we had a three-sided galvanized tray constructed to fit on the windowsill, tilted into the plastic tray, so that water drains away from plants standing on the windowsill. Because the window greenhouse was made of aluminum, it was impossible to attach hanging plants to it. We attached some hooks to the wooden window frame, projecting into the upper part of the window, with a wire stretched between them. This works well for hanging small plants. The old window sash was entirely removed. Although I have seen recommendations to leave the sash in place to create something resembling a Wardian case, I cannot imagine that this could work in a climate like ours. The enclosure would overheat violently in the summer and present a tremendous heating problem in the winter, as well as making access to the plants for the constant care they require very difficult.
When our window greenhouse was first installed, we tried to find as much information as we could about how to operate it successfully to grow orchids. Lots of information was available on growing orchids in greenhouses, on windowsills, in Wardian cases and under fluorescent lights, but virtually none on our type of situation. The methods we adopted were found by trial and error, and by attempting to combine the information we found on the operation of small greenhouses and on windowsill growing. The window has been used for over two years now; the description of our methods which follows describes our present attempts at orchid growing. No doubt these will change as time goes on.
Rhynchostele rossii, grown and flowered in the window greenhous.
One of the surprises we found in operating our window was the differences in temperature among the three different levels (the two upper shelves and the lowest "shelf" which was in fact a series of bricks standing in water in the bottom tray). The top shelf was, on the average, about 10F warmer than the bottom, both by day and by night. For most of the year the minimum night temperature at the top was around 60F or a little above. For a month or so in the summer, it was somewhat warmer than this and in extremely cold weather, in winter, it occasionally dropped to 58F or 59F. The mottled-leaved paphs are grown (with shading) on the top shelf, except in summer; this area is the brightest as well as the warmest part of the window.
The lowest level of the window has a night temperature which varies from 50F or even less in the coldest part of the winter to about 60F for most of the summer. In a prolonged, warm spell (rare on the Atlantic coast of Nova Scotia) the night temperature may be in the 65 range for a week or two. The cool-growing orchids are obviously kept in this area; in summer, the cool-growing paphs are moved outdoors but the masdevallias, miltonias and some mottled-leaved paphs are left here for the summer. When the outdoor temperature in winter goes below 0F for a few days or even weeks at a time, and this fortunately is rare, ice forms in the bottom tray. However, the air temperature around the plants does not go below 45F and they do not appear to suffer. The warmer growers among them are moved to a higher level in winter to avoid these very low temperatures.
Isabelia violacea is a beautiful miniature, suitable for the window greenhouse.
To sort out these differences a maximum and a minimum thermometer was necessary, and it would have been better to have three, one for each level.
It was apparent from the start that some form of heating would be needed in the window in the winter. Since we wanted a heater that would take up as little of the valuable space in the window as possible and also one which would not give a hot, drying blast at close quarters, we bought a 1200-watt electric heater which measures about 8 by 10 inches by 4 inches high. Its control indicated only "high" and "low" but we calibrated this so that we could set its thermostat to switch on at 50F. The heater is placed on bricks in one corner of the bottom shelf in such a way that the hot air (the heater contains a small fan) is blown along the bottom shelf. It rises up the other side to the top of the window. At first we kept some small bromeliads beside the heater to break the impact of the hot air, but, after these turned brown and died, they were replaced with clay pots filled with wet peat which seem to work effectively.
The large volume of air in the room behind the window greenhouse seems to have a buffering effect on temperature changes, so that the air in the window never heats up or cools off as much as it would if it were entirely enclosed. The roof of the window is essentially one large vent; it opens upwards and out and can be held in any position from one which admits the smallest crack of air to one which is wide open. In spring and fall the roof is opened slightly on sunny days and closed at night; in summer it is open wide by day and open to some degree at night, depending on the temperature. In winter it is not necessary to open it at all, even on very sunny days.
Since our window greenhouse was single-glazed and our winters fairly cold, it was necessary to provide an insulating layer, which we did by applying a layer of bubble plastic with propylene glycol (Collins, 1978) to all surfaces except the roof. This is left on from December to April. When the time comes to put the insulating plastic on, all the plants and the mesh shelves have to be completely removed, a troublesome job but one which permits a thorough cleanup of the window and especially the water tray. Again in the spring, everything must be taken out in order to remove the plastic.
The exterior of the window greenhouse in
winter with bubble wrap in place. This
photograph was taken after only a few months
of use; orchids subsequently replaced the
non-orchidaceous plants in the picture.
The climate of our part of Nova Scotia could be described as cool and damp in summer and cold and damp in winter. For this reason, maintaining a relative humidity which is suitable for orchids is not very difficult for a large part of the year. In summer, except on the hottest days, the relative humidity in the window is over 50%, sometimes as high as 80%; in the coldest part of the winter, if the house furnace runs frequently and the sun is bright, the humidity may fall to 20 or 25%, rising again at night. For a large part of the year, the humidity averages 40 to 50%.
The plastic tray which occupies the entire bottom of the window is kept filled with water, most of which drains in from the plants. This, however, probably provides extra humidity only for those orchid plants immediately above the tray. Most of the extra humidity comes from the plants themselves because they are packed in fairly closely, especially in winter. In addition, they are sprayed heavily. with water in the morning on sunny days before we leave for work, and again later in the day if someone happens to be home to do it. The humidity for about half the year is probably lower than ideal, but this does seem to have the good effect of discouraging diseases.
The interior of the window greenhouse in late
summer. The collection is planned so that most
flowering is from fall to spring.
We were originally very reluctant to try growing orchids on slabs because of their humidity requirements; we had had some bad experiences with slabs in our days of windowsill growing. However, a year ago we acquired a Brassavola nodosa growing on cork bark, and after doing nothing for six months after its arrival, it has now made many hearty roots and has put out two spikes of flowers. Encouraged by this, we bought an equitant Oncidium a few months ago which was growing on a tiny piece of shingle. It too seems to be growing well. Dendrobium capillipes, Prosthechea mariae and Haraella odorata mounted on cork bark have all been added recently and so far show no signs of suffering from lack of humidity. These are dipped in water every morning, rain or shine, and then given whatever misting is available for the rest of the day.
The relative humidity in our window is measured by a small hygrometer which proved, after testing,1 to read 5 to 10% too low. It is nonetheless a very useful piece of equipment to have, perhaps mainly to prevent one from over-misting on damp days.
WATERING AND FERTILIZING
Watering is one job which is certainly more troublesome in a window greenhouse than in a greenhouse proper. Although the water can be splashed around and spilt with a lot more freedom than it can on a windowsill, it is still necessary to take a certain amount of care to keep it from soaking the insulation in the base of the window or from drenching the rug and furniture in the living room. I have found that the best way to do a thorough watering is to take the plants out of the window, half a shelf at a time, and submerge them in a bucket of room-temperature water. They are then drained on a rack over another bucket and are replaced in their positions. After a few attempts one learns that it is much easier and quicker to work out a system for doing this and to follow it each time; even so it is time-consuming. These major waterings take place every three or four days in hot, dry weather, but in cool, damp weather they may be needed only every week or ten days. In between times the paphs, other moisture-demanding orchids and those in small pots are given extra waterings with a watering can.
Because most of our orchids are grown in osmunda which we dig locally, they stay damp for a fairly long time, although this is offset to some extent by the use of clay pots wherever possible. Also because of the osmunda, we fertilize only lightly, using a weak solution of fertilizer about every two weeks from late spring to early fall and only very occasionally at other times of the year. The plants that arrive in bark are also given a high nitrogen fertilizer until the time comes to repot them. Whenever a fertilizer solution of any kind is going, the plants on slabs are dipped in it.
LIGHT AND SHADING
One of the best features of the window greenhouse has turned out to be the amount of light available to it. Because it faces south and because its roof and sides are glass, it gets a very acceptable amount of light. The top shelf, directly under the roof, is by far the brightest part, and that is where we grow our cattleyas, laelias and other light-demanding orchids. The orchids on slabs are hung from a wire in this area. We found that reddish purple pigment developed quite strongly in most of these plants and take that as an indication that they are getting enough light.
Shading is put on the window gradually as it seems to be required. There is a period from mid-November to the beginning of February when little or no shading is used; then cheesecloth or thin nylon curtain fabric is used on half the roof and the corresponding half of the large south exposure of the glass. This is mainly to protect the mottled-leaved paphs which spend the winter on the top shelf for warmth. Also, at this time of year when the sun is low, a good deal of direct sun enters through the lower parts of the glass and falls on the orchids on the lower shelves.
In mid-March another layer of material is used to cover the entire roof and south side. On one occasion, when we were a few days late in doing this, our Paphiopedilum callosum, which proved itself to be the most susceptible to sunburn of any of our orchids, was badly burned under the single layer of cheesecloth.
Eventually, possibly at the beginning of May, a narrow strip of cheesecloth is hung over the west-facing glass of the window, a relatively small area. This is not necessary on the east side because of an oak tree which partly shades that side when in leaf.
PESTS AND DISEASES
So far we have been fairly lucky about pests and diseases. An occasional crop of aphids springs up, usually brought in by non-orchidaceous plants, and gets into flowers and buds, particularly those of Prosthechea cochleata. I have once or twice suspected thrips on a new paph, but these have been dealt with by hanging a Vapona strip in the window, and then sealing the window up by taping plastic over it. After many tries this seems to have disposed of even the fungus gnats. We have had two or three minor cases of rot, which seem to have been arrested by dipping in Benomyl. It is obvious that where orchids are growing in an area that is lived in it is undesirable to use chemicals more than absolutely necessary.
Our worst pests so far are slugs and snails. The slugs are mainly active outdoors and we have learned from bitter experience that as soon as an orchid plant which has been put outside for the summer shows a bud, it should be brought in immediately before the entire bud stalk is eaten. We have at times used metaldehyde slug bait outdoors, but have become wary of it after several neighborhood dogs and cats seem to have had a possible severe reaction to eating it. Very small snails seem to come in with the osmunda, and we have recently tried steaming it very lightly to try to kill them without breaking down the medium.
The only worrying possibility in this area that bothers us at the moment is the presence of slight light and dark green mottling on the leaves of a couple of oncidiums and an Odontoglossum. We keep hoping that this may be nutritional, or in some way an effect of our conditions, but we are afraid that it may be due to a virus. If so, watering by dipping all the plants in the same bucket of water seems likely to spread it, as does keeping the plants in such close proximity to each other.
We know that orchid plants can coast along on their reserves and may not show the effects of poor culture for some time. We have been growing orchids in our window greenhouse for only a little more than two years and no doubt it is too soon to be certain about our results. So far, we have over fifty orchids growing in the window and the following plants have been with us for more than a year and have flowered well: Paph. insigne, Paph. fairrieanum, Paph. spicerianum, Paph. sukhakulii, Paph. callosum, Paph. Maudiae 'Coloratum', Paph. niveum, Paph. hirsutissimum, Paph. villosum, Masdevallia tovarensis, Bulbophyllum guttulatum, Oncidium cheirophorum, Onc. ornithorhynchum, Brassavola nodosa, Dendrobium longicornu, Isabela(Sophronitiella) violacea, Prosthechea cochleata, Rhynchostele rossii, Cuitlauzina pendula. There are a number of others that we have had for a year or two which seem to be making healthy growth and of which we have hopes of bloom. Paphiopedilum bellatulum and Paph. haynaldianum appear to be about to put up bud spikes. Some others more recently acquired have already bloomed or are growing well. There are also those stubborn plants that stand still, for a long time, perhaps recovering from the shock of new conditions. Nevertheless, we feel that our orchids are growing better than they did on the windowsill and that we are now capable of growing a much greater range of plants.
The best measure of the success of the window is the behavior of the plants which were already growing on our windowsills that were moved into our window greenhouse. First there are the paphs, which, although they have always bloomed, now make more rapid growth with less dying out in the middle of the plants and probably do produce more flowers. Our Oncidium cheirophorum used to produce flower stems that stuck in the bracts, shaped like hairpins, unless they were released at an early stage of development, and in addition it frequently had pleated leaves. The plant now produces straight stems of flowers without any difficulty, and for the first time has produced two flower stems per pseudobulb. Its leaves do not pleat now except on rare occasions when we are on vacation at a critical time in its development. Masdevallia tovarensis, which was going rapidly downhill when grown on the windowsill, producing fewer and fewer flowers and leaves, has now reversed this trend, producing abundant new leaves and appearing green and fresh instead of yellowing and dried up.
Growing orchids in a window greenhouse combines some of the advantages (and disadvantages) of windowsill growing with those of a greenhouse. The relative humidity that can be maintained in the window is probably its biggest advantage over the windowsill; the next is the longer hours of light available, as well as brighter light. It is also easier to water, and, of course, it accommodates more plants. In addition, the window greenhouse seems, at least under some conditions, to provide a wide range of temperatures. Most of these advantages, of course, would be considerably increased by the use of a real greenhouse. However, the big advantage that a window greenhouse has here is that it displays the plants in the living area of a house. The plants can be admired and looked after while going about one's everyday affairs. In addition, the time required to look after orchids is less than that required by a greenhouse, and of course both the construction and operating costs are considerably lower. - 834 Marlborough Avenue, Halifax, Nova Scotia, Canada B3H 3G6.
Collins, R., (1978). Insulating a Northern Greenhouse. Amer. Orchid Soc. Bull. 37: 100-101.