It’s not just people and pampered housecats that benefit from a warm blanket in the winter, plants appreciate one too – especially those that are adapted to gentler climates. This past spring, we witnessed some surprising plant survival stories as a result of the protective blanket of deep snow that persisted through most of last winter. In my yard, parsley and gladiolus returned for an unexpected repeat performance. There’s still time to prevent cold injury to marginally-hardy plants, using a man-made version of the “blanket” principle, since we can’t count on a continuous cover of deep snow like last year’s. The easiest and cheapest method is to rake up some oak leaves and use them for insulation. Oak leaves are preferred because they are sturdier and have less of a tendency than more delicate deciduous leaves to pack down over time. An old-fashioned nurseryman’s trick is to fill a peach basket with oak leaves, turn it upside-down on the plant to protect, and weigh it down with a brick or stone placed on top. Obviously, this will only work on plants small enough to fit under a peach basket. I’ve overwintered a rosemary plant in my Zone 6 garden for more than 10 years using this method. Now that the plant is large, I surround it with a hoop of chicken wire and simply fill the hoop with oak leaves. This variation will accommodate larger perennials and small shrubs, buying you protection a full zone warmer than where you are.
Wrapping larger plants, such as fig, with insulating material (burlap or other fabric) will help them survive the winter in the milder areas of the state (Fairfield County and the Connecticut River Valley). Wrapping is also a good practice for evergreens that were planted in the fall or are exposed to windy sites; both conditions make these shrubs vulnerable to winter desiccation. Avoid plastic as a wrap material; it can create a greenhouse effect on sunny days which could cause the plant to lose dormancy, making it vulnerable to cold damage. To avoid this, protection must be removed toward the end of the winter while the weather is still cold. It may be necessary to replace the covering quickly if late, extremely cold weather is expected.
An easier option may be to grow marginally-hardy plants in a container and once they’re dormant, move them into a garage or cellar with a temperature consistently close to freezing. Occasional light watering is the only care necessary until it’s time to move the plant back outside in the spring. Oleander and geranium (Pelargonium) can also be overwintered this way.
Plants that produce bulbs, corms, rhizomes and tubers when dormant (but aren’t hardy in our area) can be stored for the winter and replanted in the spring. The most common (and rewarding) are:
Loosen the soil around the base of the plant with a garden fork. This late in the season, the leaves will probably fall away from the corm easily, so a little fishing in the soil may be necessary. Let the corms dry indoors on newspaper or screen for a few days. The cormels (babies) can be removed from the corm and saved for additional stock. Store the dried corms in paper bags or onion sacks. Label the bags and hang them in a cool, 40-50 degree dry location, away from marauding rodents, until spring.
If gladiolus is grown in a cluster, it may be worthwhile experimenting with a deep mulch of leaves for winter protection. The first year, do this with a few glads that you’re willing to risk losing.
Dig dahlia clumps carefully, as tubers break easily. Allow the clump to dry on sheets of newspaper or cardboard. Pack the tubers in dry sand, peat moss, wood chips or granular vermiculite. A storage temperature of about 45 degrees is ideal. Small tubers can be kept in a zip lock bag or wrapped in plastic in the vegetable bin of your refrigerator. Check periodically for rot. A dusting of sulfur will help to prevent bacteria or mold from developing.
To store cannas for the winter, use the same process as for dahlias. Unlike gladiolas, which should be stored cool and dry, the rhizomes of dahlia and canna need to retain some moisture; they should not be allowed to dry and shrivel during storage.
Before the fierce winds of winter begin to blow, protect those perennials and shrubs that may benefit from a blanket. If the ground isn’t frozen, glads, cannas and dahlias can still be lifted. Seize the moment!