During the summer, many if not most of my houseplants go outside. I park them in the shade–say, under a tree–and they thrive there all summer. As soon as the temperatures begin to drop into the 50s and 40s overnight, I begin bringing my plants indoors.
I begin with the plants that are most sensitive to cold temperatures. Thus, as soon as the night-time temperatures start to drop below 60 degrees F, I bring in my orchids, the banana tree, and any other plants that are particularly sensitive and valuable, such as the bay tree that was a birthday gift from my sister. As fall progresses, the overnight temperatures will continue to get cooler and cooler.
I try to have all my sensitive or valuable plants inside before the temperatures drop to 45 degrees F or colder (about 10 C), and well before the first-frost date. That way I won’t be surprised by an early frost and lose a favorite houseplant or annual to it.
When bringing plants inside, I always inspect them carefully for insects and signs of disease. Often in the summer, insects take up residence in house plants. If I find insects on the leaves, I carefully wash all the leaves to remove them. If there are insects in the soil, I usually remove the plant from its pot, inspect the roots and remove as much soil as possible, and repot the plant in fresh soil. Generally, I avoid using commercial chemical insecticides indoors.
Often, I keep plants just brought in from the outdoors away from my other houseplants for a while. That way, if they have picked up a disease, it won’t spread to the rest of my plant collection before I detect it.
I’ve found that for me, one of the most important consideration in overwintering plants indoors is meeting their light requirements. For my houseplants, I can just put them back in the same window in which they were growing the previous winter.
For tender perennials that I’m growing inside for the winter, such as geraniums or coleus, I try to place them as close to a window as possible, often the sunniest spots available. Generally that means I overwinter tender perennials that people usually grow outside, such as geraniums, in or near the large, south-facing windows in my house. When I run out of window space, I move some tender perennials to the grow lights in my basement. Rotating plants between the window and the lights is sometimes helpful.
My grow-light set-up is not fancy. I have suspended a large shop light from the ceiling so that it sits about 24 inches above the table on which I grow the plants. I put special grow-light bulbs into the fixture, because they have a different spectrum than ordinary fluorescent tubes.
Dry indoor air in the winter can also be detrimental to plants. When possible, I overwinter my plants, especially my orchids, on humidity trays. The plants sit on a grid above a tray that I fill with water. This provides moisture to counteract the low wintertime humidity. Another option is to fill a tray with gravel and moisten or wet the gravel. The plants are grown set on the gravel, above the waterline. If you aren’t willing or able to buy humidity trays, you can make your own,.