The temperatures are dropping and our floral and faunal friends are at risk. And while winter may be a quiet time for gardening, there are still things to be done to keep your plants growing and blooming once the temperatures rise again.
Overwintering is the process of bringing a plant inside to keep it from dying in the cold. When done right, this allows you to take it back outside in spring for another glorious growing season. Although many perennials go dormant by themselves, some more tender perennials—such as coleus, begonias, rosemary, and fuchsias—need protection from winter’s cold touch.
For in-ground plants, you can insulate them with a thick layer of mulch or dig them up, moving them to a cold frame or basement when nights begin to cool, but before the first frost. Gently remove most of the garden soil from around the roots and then repot the plant in good commercial potting soil that has fertilizers in it for winter keeping. Garden soil is not good in containers as it balls up.
Storing plants for the winter, just like growing them, requires attention to detail. The plants will need some light, occasional watering, and temperatures above freezing. Most plants will tolerate a few months of lower light levels while overwintering. Keep your eyes open for yellowing or pale foliage, dropping leaves, or leggy growth. These are signs your plant needs higher light levels. Watering is still a necessary part of your plants’ care: Although they aren’t actively blooming in this time, your plants are still thirsty; up to a half inch of water each week is recommended.
If a plant is too large to bring inside, you can take a cutting instead. Cut off a section of the plant three or four leaf nodes in length with hand clippers. Place it into a small container of potting soil, add a little water, and pat down the soil around the cutting.
You don’t generally overwinter annuals, because by definition they are plants whose life cycle is complete in just one year. Petunias, zinnias, and marigolds, for example, emerge from seeds, come to maturity, bloom, set seed, and then die—all in one year.
Each perennial has its own specific needs. Overwintering fuchsias is rewarding and well worth a try. Some types are quite hardy and will even survive outside if in a protected spot shielded from freezing temperatures and harsh winds. However, I recommend moving garden varieties into the garage, greenhouse, or basement. A cold frame or sheltered porch where they can spend the winter in a semi-dormant state would also work. Prune severely, leaving stems with only three buds. If growing in the ground, cut them back to half their original size, then mound with protective mulch or compost to cover half of the remaining plant. Mulch helps your plant retain moisture and adds extra heat, keeping roots happy as the mulch decomposes and adds rich organics to the soil.
Geraniums are one of the more successful candidates for overwintering. Dig them up in the fall before the first frost and remove all soil from the roots. Replant for winter in either peat, sand, or potting soil. I remember my mother simply cutting them back and then hanging them upside down, bare-root, in the garage. When the stems started to leaf out in spring and the danger of frost was over, they would be replanted into pots or directly into the garden beds.
Dahlias and cannas, Willamette Valley favorites, should be carefully dug up before the onset of heavy rains. Cut the stems back four to five inches, then wash the dirt off the tubers. Examine them closely and cut away any damaged or diseased parts, then set them out into the sun to dry a bit. They do best stored in dry sand, peat, or sawdust. Keep them in a cool, dark place like the cellar or garage until spring, when it’s time to divide the tubers by cutting the clusters apart to be replanted.
With any luck, you’ll get a good deal of satisfaction next summer from the plants you overwintered.