By Tom Oder
One of the most frequently asked questions about winter gardening is whether extreme temperature swings will harm or kill ornamental plants.
In general, the answer is “no.” Plants have a genetic ability to sense atmospheric changes and adjust in advance of them. While warm winter temperatures do induce growth and flowering, cool temperatures slow down the growth rate and race to flower.
The time when plants are most vulnerable is in the spring when periods of warm weather increase and suddenly there are several nights with temperatures well below freezing.
While plants generally will survive hard winter freezes, blossoms on winter-flowering plants such as camellias and plum and cherry trees aren’t so lucky.
When buds are swollen and blooming is imminent, a hard freeze can damage the buds. The damage can remain hidden until the flowers open and then show up in the form of brown spots on the petals. In some cases, the entire bud may freeze and drop off the plant. Fully open flowers will either turn a sickly brown or fall to the ground.
To avoid the disappointment of unsightly flowers or losing them altogether, cover plants that have buds and open flowers with an old sheet or a commercially available frost cover. (Don’t use plastic: It can quickly create an oven effect when the sun shines on it.)
You can also trick Mother Nature by cutting the buds in advance of the freeze and bringing them indoors to let them open in the house. If a freeze is predicted before buds have been set, there is no need to add a protective covering.
Here’s a list of “dos” and “don’ts” to help your plants survive hard freezes and to help you enjoy the blooms on the many beautiful winter-flowering plants.
Continue to plant — as long as the ground is soft enough to dig a hole.
Add mulch. It will help keep root temperatures stable.
Add compost. It supplies organic nutrients to the soil (but no more than three inches thick).
Water. Watering in advance of a predicted freeze helps plants, especially potted plants and annuals, make it through a hard freeze because it allows plants to take up moisture before the ground is frozen and prevents water from reaching the root zone. Be sure to hydrate above-ground shoots as well as the roots.
Give container plants extra protection. Cover with frost cloth or other heat retentive blankets and move pots and other containers close to the foundation of the house or under eaves.
Bring in houseplants. Spray both sides of the leaves with an insecticidal soap and water thoroughly with an insecticidal drench that is safe for people and pets to kill hitchhiking critters. Position plants indoors where they will receive indirect, bright light for at least five hours a day. Be sure to keep them away from drafts and heating vents and water sparingly because most houseplants do not actively grow in winter.
Fertilize. This is a time for garden plants to go dormant and rest. Forcing them to start new growth before the ground warms in the spring not only interrupts this period when they are rejuvenating but ice storms and temperatures below freezing or even hard frosts will kill tender new growth.
Skip your regular watering cycle. During dry periods when the ground isn’t frozen or covered with snow, a once-a-week deep watering is beneficial. New plantings especially need to be watered in.
Worry about bulb foliage. Leaves of daffodils and other spring-flowering bulbs should be just fine during temperature dips.
Have other winter gardening tips? Leave us a note in the comments below.
Photo: Flowers on a large cherry tree, Prunus ‘Peggy Clark’, open early in the winter every year at the Atlanta Botanical Garden and then fall to the ground when they suffer cold damage from the inevitable hard freeze. (Tom Oder)