A large number of gardeners, for one reason or another, need to overwinter plants grown in containers. There are basically two types of plants that fit this condition -- hardy types, such as perennials and woody shrubs and trees, and non-hardy types, such as annuals and geraniums.
The hardy types are best left outside with some protection, while the tender plants must be stored indoors. It must be said from the outset that the procedure for saving these plants is not an easy one and success is far from guaranteed.
Gardeners should approach the task as a project designed to hone their gardening skills, not an attempt to save money. Any money saved is often lost in lower-quality plants and additional equipment and labor.
Let's tackle the hardy plants first. Some might ask how a hardy plant gets into a container to begin with. Why was it not planted directly into the ground?
There are hundreds of possible answers. Plants might have been purchased late and are scheduled for a garden to be built next year, or they might be cuttings or seeds that were started in midsummer and never reached planting size.
The problem at this point is not how they got there but how to get them through the winter. The best solution in all cases is to bury the pot in the ground and mulch it with bark or wood chips.
The roots of almost all plants are not as hardy as the tops. And because soil temperatures do nearly reach the low levels of air temperatures, Mother Nature naturally protects the roots in soils where temps do not dip below the high 20s.
Although it's riskier, gardeners can also place these pots in a protected spot along the east or north side of a house. Snow is likely to settle in these areas to further protect the plants, and the house may add some additional heat.
Some may opt to cover the plants with supported plastic, burlap or another covering. The risks in covering the pots are twofold. Too much heat can build up under plastic that gets sun, and mice find these areas to be perfect hiding places. Despite the hazards, covered plants are better-protected.
Saving annuals, hanging baskets and geraniums is also not a project for the beginner. The main difficulty here is not the overwintering part; it is getting the plants to look good enough to go back outside again next spring.
Gardeners wishing to give this the old college try are probably best advised to keep the plants growing in the sunniest window available. Rather than saving the mother plants for next year, cuttings should be taken from them in January and February.
These cuttings are rooted in an artificial soil mix after dipping in a rooting hormone. A warm spot with bottom heat and light helps.
After rooting, the plants need to get as much light as possible to minimize stretching. A windowsill, although bright enough, is also hot on sunny days, and plants grow thin and spindly. A small greenhouse and/or a bank of artificial lights in a cool room will work much better.