Why do we all think we need a greenhouse? Some of us may rely on them for sheltering plants through cold winters. Some of us grow seedling late in winter, for an early start in spring. For some of us, greenhouses are where we grow plants that would not be as happy out in the natural climate. There is a multitude of uses for a greenhouse; but really, how many of us need one?
When I grew citrus trees, I needed a greenhouse. It was where the freshly grafted cuttings were rooted. (Citrus are grafted and rooted simultaneously, literally by grafting the scions to the unrooted understock, and ‘sticking’ the combination as a cutting into rooting media.) The greenhouse contained humidity to prevent desiccation, and warmth to stimulate root development.
From there, freshly rooted citrus trees were canned and moved out of the greenhouse and into a partly sheltered location to harden off. Once well rooted, they graduated from #1 cans to #5 cans, and were moved out to the field where they were completely exposed to the weather. All those acres of citrus tree production used only a few hundred square feet of greenhouse space.
Most of us are not rooting freshly grafted citrus cuttings, or many other cuttings that can not be rooted out in the real weather. Really, in this particularly mild climate, not many of us have any practical use for a greenhouse. It is just something that we believe a well outfitted garden should include, even if we need to procure a few rare and needfully tropical plants to prove it.
Contrary to what anyone says, plants in greenhouses need more work than those of comparable substance outside. They need to be watered even during rainy weather. They need the vents opened during warm weather. Most pathogens proliferate much more aggressively inside a greenhouse than outside. Greenhouses can create almost as much extra work as they eliminate.
The saran house in the picture above works nicely for a few plants that want a bit of shelter. Some plants are recovering from removal from landscapes, and will eventually get planted back into other landscapes. We grew a few of these plants from cuttings. They all get a bit of shelter from hot direct sunlight in summer, and frost in winter. We grow many more plants outside.
Shade trees, even the nearby deciduous box elders, could provide as much shelter as the saran house provides. Nothing fancy is necessary. Plants that need any more shelter than what they could get here or under a shade tree are useless in our landscapes. After all, our landscapes, by nature, are all outside. The plants that go into them must therefore be able to survive outside.