There are many different tropical plants sold as houseplants and annuals, but for overwintering, we are going to break them up into 3 "types."
#1. Growing and Blooming
If you have a home with bright light and lots of space you can keep your tropicals growing and blooming through the winter. 65 degrees during the day and 55 degrees during the night are actually the perfect winter temperature for most tropicals.
Water moderately - you want keep the soil on the dry side during the winter months, but to keep the humidity at around 45%, you need to spritz the leaves with a misting bottle regularly or set out a shallow dish of water near the plants. (Most homes with forced air heat have humidity levels of around 20% during the winter months.) Make sure the plants get plenty of light (12 hours) and get plenty of space and air circulation (a fan can help) to help prevent indoor pests.
What to do about whiteflies, scale, and aphids.
Plants to keep growing and blooming: Fig trees, citrus trees, palms, geraniums, oleander, tropical ferns, Christmas cactus, jasmine, hibiscus, bougainvillea, plectranthus, agave, echeveria
#2. Resting Dormant
I've read articles about forcing dormancy for winter storage that include digging out bulbs, wrapping them in moist packing materials, misting the packing materials through the winter, carefully monitoring light and temperatures, and I have to say it all sounds like a huge hassle. Here's what we do (and it's easy!):
For bulbs (canna lily, caladium, elephant ears, and sweet potato vines) let the leaves get hit by a light frost, then bring inside and stop watering the plant. Let the soil dry out, let the leaves turn brown and the cut the plant and foliage back. Put the whole pot in a cool dark space (an unheated basement or garage, or a root cellar - we keep them in a cool room under a table!). In the spring pull out the pots, expose them to light, and start watering.
For woody-stemmed plants (brugmansia, bananas, tibouchina, and jasmine) expose them to low night time temperatures 40 to 50 degrees and then move them to a cool dark space. Stop watering and if you have the space you can leave the plant standing until the spring (we cut them back as soon as the leaves drop). Two times during the winter you want to give your woody-stemmed tropicals a little bit of water (a half gallon or so), and in the spring expose them to light and start watering (and fertilizing).
That's it - easy-peasy! Cool, dark, and dry = dormant.
#3. Cutting and Propagating
If you don't have a lot of space to overwinter plants, cuttings can be the answer. Unfortunately, this only works for soft-stemmed tropicals.
Soft-stemmed topicals (geraniums, coleus, and plectranthus) can be propagated by clipping off succulent new growth (woody stems won't root) and place the cut end into water. When roots sprout, pot into soil-less mix in a small 4 inch pot. Once potted place them in full sunlight and FEED THEM! Weekly fertilizer is must to keep them healthy. In the spring, after the last threat of frost you can put them out in larger containers or plant them in your garden.
Tropicals can add color and drama to your garden all summer, and with these 3 easy techniques, you can enjoy those tender beauties year after year.