Focus your eyes on your summer garden or patio and you will likely be able to find a plant that has been purchased as an annual when it is really a perennial in its growing zone. Garden centers and nurseries bring in exotic flora to tempt and delight us with new and more amazing color, scent and form. This excellent marketing approach is difficult to resist after a winter spent inside, chafing to grow spectacular flowers, fruits and vegetables. Many gardeners chose plants that will not survive their winter temperatures as annuals, but some of these tender flora can be saved over the winter, indoors. The result is money saved, a vigorous plant with a developed root system and the satisfaction of caring for a difficult specimen.
There is more to storing a living plant indoors than just potting it and bringing it inside. First, make sure it is not carrying any hitchhikers that will infest your house plants. This may necessitate spraying off the leaves with sharp bursts of water, using a horticultural oil or soap, or even just hand picking. Once you are sure your plant friend is free of pests, transfer it to a pot big enough for its root ball that is filled with an appropriate plant mix. Plants that require a rich loam will do fine in good commercial potting mix with a little compost mixed in. Other plants require dry soil and superior drainage and the addition of some grit or fine sand will help them adjust to their new home. Pots should be freely draining and unglazed to allow for evaporation of excess moisture to prevent rot.
Place large pots on casters so they are easy to move in and out when the time comes.
The location in the home interior is the next order of business. Most tropical plants need a warm site with temperatures no lower than 50 degrees Fahrenheit. Others like brugmansia, passion flower, figs, datura and plumeria will go dormant in a basement or other cooler location where temperatures are even cooler but never freezing. Lighting is another factor. For plants from tropical regions, place the plant in any but the north windows. Croton, bougainvillea and hibiscus need at least 5 hours per day to keep them happy. Specimens from tropical rainforests are used to warmth but need less light as they are generally covered by a canopy of large trees and enjoy indirect, dappled light. Plants that can stand a light frost will usually be fine in the cooler range with grow lights. Any plant that goes completely dormant or drops all its leaves should be placed in a dark room with a temperature range that closely matches its native zone. But of course, there are the dilettantes that need bright light and really warm temperatures. Citrus, palms and geraniums fall into this category.
Care of overwintered tender plants is minimal. Any that are in active growth may get leggy and require trimming. These also have moderate water needs. Plants in the dormant state rarely need water as they are not currently in the process of producing roots, fruits, flowers or even foliage. Turn plants in lighted situations a quarter turn weekly to promote even growth. Some plants will go into shock once moved indoors and drop all their leaves. If you don't see any leave nubs within a couple of weeks, move the plant to a dark or dim area. Fertilize in late winter to early spring. At this time, cut back woody stemmed plants to prepare them for new growth.
Saving bulbs, tubers and other underground growth organs is easier than bringing in the plant. Caladium, sweet potato vine and canna are examples of easy to winter tropical flora. Cut back the foliage just before the first frost and dig up the tubers or bulbs. Wipe off the dirt and let the organs dry out for a few days. Then wrap them in moss and place them in a paper bag or box in a dark location with temperatures between 40 and 50 degrees Fahrenheit. Replace them in the ground once the soil is workable and temperatures during the day are at least 60 degrees Fahrenheit with no nighttime freezing.
Spring introduction is a slow and steady process. Acclimate the plants gradually to outdoor temperatures with brief periods outside daily once all danger of frost has passed. The plant also needs to get used to brighter outdoor light. The first few days move it to a sheltered location where the lighting is muted or dappled. Then begin to position the pot where more and more light is evident. Start with just a few hours and build up to a full day within two weeks. You will also increase the frequency of watering at this time. Make these changes slowly so the plant is not stressed and slips easily into a spring growth pattern.
If you are not sure what the best care for your tender perennial is as a houseguest, take cuttings. Try one of the methods and if it doesn't work at least you have a baby plant with which to start over.
As a rule, it is worth trying one of the methods, since the plant will succumb outdoors without any intervention on your part. Remember to mimic the plant's native regional weather and water characteristics as well as you can.