“When do I bring my houseplants back indoors?” and “Can I keep my mandevilla vine and hibiscus plant over the winter?” or “How can I avoid those fruit flies or fungus gnats I get when I bring plants inside for the winter?” These are typical questions I get from clients, customers, and my GardenLine radio audience on WXTK. It’s time to bring plants inside, and that’s this week’s weekend project.
My general rule of thumb is that most houseplants, annuals and tropical plants should come inside when the night time temperatures are consistently dropping below 50 degrees fahrenheit. Most tropical plants don’t like being in forty degree weather. Additionally, at such points in the fall most people’s heating hasn’t come on very much so the plants can get used to lower light levels before they have to adjust to the central heating as well.
Many summer annuals and container plants are worth overwintering inside, although if you’re wondering about that mandevilla vine, read my advise at the bottom of this post. As you bring plants indoors, clean them up and be sure to check on the sides and under the pots for slugs and other random wildlife.
When it comes to fungus gnats, those pesky small “fruit flies” that seem to come with plants as you bring them inside, there are several ways to keep these in check. The first is with gnatnix, a product made of recycled glass. Growstone Gnat Nix! Fungus Gnat Control, 9-Liter When you put this over the surface of your indoor plants it prevents larvae from hatching out into the air and keeps adult gnats from getting to the soil to lay their eggs. And it’s made in the USA!
Other ways to control fungus gnats include the use of yellow sticky cards and a product containing spinosad. See my post from last winter about successfully controlling the gnats this way.
Many people wonder if they should put a layer of rocks and water under their plants for moisture. This is one of the myths I address in my book, Coffee for Roses: …and 70 Other Misleading Myths About Backyard Gardening. The short answer is don’t bother. You will need saucers or a tray under the plants, however, to catch the water as it runs out the drainage hole in the pot.
Many tropical plants live well from year to year given enough sunlight indoors. They might shed leaves during the winter, and not look particularly wonderful from January on, but most can be cut back in February and started on a regular fertilizer program. If you’re going to repot January through March is a good time to do so. When they go back outdoors they spring to life fairly quickly.
Mandevilla vine (aka Dipladenia) are a tad more problematic than other tropicals. Although they will live just fine indoors, because the hours of daylight aren’t right the plants that homeowners keep from year to year don’t start to flower until August. You see, they have to go through the long days of summer and start into the shorter days of fall before they will flower. Commercial growers manipulate this with artificial lights so that when you buy your mandevilla vine they are in flower in May and will continue to flower all summer. Home gardeners seldom want to invest the time and money into artificial grow lights to make this happen. I decided long ago that it was worth buying the mandevilla vine fresh from the grower every year. I’ll save the sunny window spaces inside for more satisfying plants.