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If you live where temperatures drop below freezing in the winter, you should protect your perennials from the cold. This will prevent the crown and roots from freezing and dying.
Frost Versus Freeze
Frost is when ice crystals form on plant foliage. It generally occurs when the temperature is 36-32 degrees Fahrenheit. Some plants are susceptible to cold injury, and their foliage dies dramatically at the first hint of frost. Squash, for example, turns into a goopy mess when the first frost hits. Hardier plants can withstand frost, but some foliage may get brown tips.
A freeze is when the temperature dips below 32 degrees. Many plants will lose their foliage at this point when the water in the plant cells freezes. Other plants do not lose their foliage, but it turns brown and dies. Even when the foliage dies, the crown and roots of the perennial stay alive. The roots never go dormant, so they need air and water. They do reduce their activity in the winter.
When To Prune
The dead foliage of perennials can be removed by cutting it back to the ground after the first hard freeze. Do not cut back the foliage until it dies. Many plants shift the starch and other nutrients in their foliage to their roots to prepare for winter. If you cut the foliage prematurely, that transfer doesn't happen. The plant will not be able to start growing in the spring or won't grow as well.
There has been a shift in the recommendations to always remove dead foliage after a freeze. Some researchers recommend leaving the dead foliage standing and only pruning in the spring as plants start to grow again. Plant material left over the winter helps wildlife, who can feed on the seeds. Insects like native bees may be pupating inside the dead stems of the plant. The standing foliage can also offer shelter to birds and small mammals during storms.
Leaving the plant material over the winter helps insulate the crown and roots of the plant. This reduces winter injury and lets a plant green up earlier in the spring. If your plant has struggled with disease or pests, remove the dead foliage after the first hard freeze and put it in the trash, not the compost heap. This allows the plant to start anew in the spring without the disease or pest posed to come back when new growth forms. The only pruning you should do before the first hard freeze is to remove broken or diseased parts of the plant. Pruning too early can result in a burst of new growth. The tender new growth will die in a hard freeze and may injure the plant when it does so.
Mulching Over the Crown
If you remove the plant material when it dies, you must use mulch to protect the crown and roots. How much mulch depends on how cold the area gets in the winter. For a temperate region, use 3-4 inches of mulch. Cover the crown of the perennial for an icy area with four to six inches of mulch.
In the spring, when the weather is warmer than freezing, remove the mulch from the perennial crown so it can start growing. You can leave the mulch around the plant, but make sure it doesn't touch the trunk or stem. Wet mulch against the plant can cause rot.
Watering During the Winter
The roots of a plant continue using energy even when it is freezing outside. The roots get water in areas with lots of snow when the snow melts. In cold areas without snow, the roots still need to be watered. Water the area around your perennials, trees, and shrubs deeply before the first freeze. The water will stay accessible when the soil above it freezes. During the winter, water deeply once a month. Pick a day when the temperature is above freezing to water.
Sudden Freezes
In the southern United States, the weather has been much warmer than usual in the last few years. Plants do not go dormant on time. A sudden freeze hitting a plant that isn't dormant can injure or kill it. The same plant in an area where the temperature gradually declines stays relatively cold, then warms up in the spring and can withstand much lower temperatures.
Covering perennials before a sudden freeze is essential to protect them. Using frost cloth or quilts, cover the plant thoroughly. Make sure the cover makes good contact with the ground. Weigh the fabric down with weights or rocks. A cover that flaps in the wind can do more damage than you would believe to your plant and isn't effective at sheltering the plant from the cold. In the past, people were told to put a light bulb under the fabric to help heat the area and keep the plant from freezing. LED lights generate very little heat and will not help the plant stay warm. If you put an incandescent bulb under the cover to heat the plant, ensure the bulb does not touch the plant or the cover, or you may have a fire.
Fertilizing Appropriately Is Important in Cold Weather
Fertilizing a plant too late in the fall with a lot of nitrogen usually results in a burst of new growth. The tender new growth cannot tolerate the cold and dies back. This often damages the plant. Ensure that any fall fertilization stops four to six weeks before the first freeze date in your area.
Pick Native Plants
Native plants are likely to endure the winter than non-native plants. Some people think native plants are all unattractive. Many native plants are beautiful and live long lives. Think of black-eyed Susans, with their brown middles and bright yellow petals. Purple coneflower, with its purple petals, is also very attractive. Both are native to North America. Trees such as redbuds or dogwoods have beautiful flowers and are hardy. There are attractive perennials, trees, and shrubs in every area. They are adapted to the amount of rainfall the area receives, need little fertilizer, and attract wildlife.
Need Help Choosing?
At TN Nursery, our staff can help you discover the native plant for every niche in your landscape. Call 931.692.7325 for answers to your questions and to order plants.
