Prepare Plants for Winter
Freezing temperatures, heavy snow, and drying winter winds present special challenges for Northern and Midwest gardeners.
Preparing plants and gardens for winter does not necessarily have to be complicated or a lot of work. One of the simplest things you can do is select plants that thrive in your region and keep them healthy right up to frost. There are many homeowners who simply select plants, shrubs and trees that are hardy to a zone or two north of their region, water them occasionally and everything does pretty well. Assuming that you may a greater variety of plants with varying levels of hardiness, you may need to invest just a bit more care into your plants and gardens, let’s start with the basic preparations for winter.
Water
When temperatures plummet and the air’s moisture content is low, which generally happens in winter, plants lose their moisture even though they are not actively growing. If the ground is frozen and the plant cannot move moisture from the soil through the plant, injury will occur. The longer these adverse conditions prevail, the more extensive the injury. When we experience a winter with long periods of extreme conditions combining unusually low temperatures and icy winds, a great deal of damage can be caused to evergreens as well as deciduous shrubs. Afternoon sun exposure causes additional stress, as the sun is quite warm even in winter, further drying the plants. Damage from wind, sun scald, and lack of moisture (called desiccation injury) is very evident in evergreens with needles because the needles turn brown and generally drop in spring. The damage may occur on one side that is most exposed to wind and late day sun, or be severe enough to occur on the entire plant. Some may not recover from the stress. Deciduous plants naturally reduce their water content to acclimate to winter. Dropping their leaves is a way to dramatically reduce overall water content.
Water evergreens thoroughly in fall before the ground freezes. The soil should be moist but not waterlogged. If the ground freezes late, continue watering as long as possible to ensure the plant goes into winter with the highest moisture content possible.
Water deciduous shrubs and trees thoroughly in fall before the ground freezes to allow the plant to reduce water intake on its’ own. Withholding water will not aid the plant in acclimating itself to winter, rather it may reduce the plants’ winter hardiness. Watering can be reduced as freezing temperatures approach.
Plants that continue to grow late into autumn but are susceptible to early freeze damage, such as rhododendrons, evergreen azalea, boxwood and holly, should also be well watered until the ground freezes.
Fertilizer
Fertilizing helps your plants go into winter strong and healthy, however you do not want them to be actively growing right up to winter. Fertilizing your plants will encourage new growth, which can be damaged by freezing temperatures. And actively growing plants will not acclimate themselves to the changing weather.
Reduce the amount of nitrogen applied by mid to late July to slow the growing process. Mid to late summer fertilization should be applied at about half the nitrogen rate. Potassium may be as much as doubled.
No fertilizer should be applied to plants in late summer, after about mid August.
(Annual flowers and vegetable gardens can be fertilized at full rate until frost)
Clean up Debris
Leaves, stems and branches left lying about the garden may harbor insects and disease, that will be more than happy to re-infect your plants next spring. Dispose of all diseased plant material by bagging or burning. Healthy trimmings may be composted.
If any of your plants were afflicted with leaf spot or other diseases and fungus that infect leaves, the foliage should be removed and bagged or burned. After the plant has died back, carefully snip off all infected foliage to be disposed of.
Mulching
Just about the time the soil is freezing, it is time to pile on the mulch. Mulch does not keep your plant warm through winter, it helps the soil to maintain a more constant temperature and also helps it to retain moisture.. Soil that freezes, thaws, and freezes will eventually damage roots and may heave your plants up out of the soil. You can choose from a variety of bark products from your local garden center, and it should be applied 2 to 2 1/2 inches deep. Or apply compost, peat moss, or straw. Be careful about using hay that is often available for Halloween or autumn decorating, it is often loaded with seeds that will sprout up like crazy next spring. Pine boughs are excellent for covering evergreen shrubs to protect them from winter sun scald and wind burn. If you use a real Christmas tree, recycle it by protecting your living shrubs. Extra large leaves can work well for smaller shrubs and plantings.
If you applied summer mulch for weed control and moisture retention, remove it from around the base of shrubs and trees to form a “donut” by mid August (it should not have been applied right up to the trunk or too deep directly around the trunk in the first place). This will allow the plant to begin its’ acclimation to winter by exposing it to the slowly reducing temperatures. Plants and perennials that require additional protection to survive your winter will need a deep layer of mulch added by mid November or later, when the ground is beginning to freeze. Do NOT add deep mulch too early or your plants will not be slowly exposed to colder temperatures, allowing them to acclimate for winter. Leaves, other than oak or beech, are not recommended for mulching. They tend to mat down and prevent air from reaching the soil, damaging your plants. Grass clippings are also less effective than other mulching materials.
Mulch can be applied around newly planted trees, shrubs and evergreens in mid November, before the soil begins to freeze. This will keep the soil a bit warmer a bit longer, allowing your new plant to take more time establishing roots.
Deciduous Sun Scald
Young deciduous tree trunks can be damaged by sun scald, splitting the bark. This is caused by rapid thawing of the bark in warm winter sun. Wrap the trunks with tree wrap paper available at garden centers or with burlap in mid to late autumn to prevent this injury.
Prepare New Garden Beds
Autumn is a great time to prepare the soil for new garden beds, unless erosion over winter may be a problem. There is so much more to do in spring, it will be nice to have new beds ready to plant. If you remove sod for a new bed, put it in your compost heap.
Also be sure to see “Tucking in for Winter” for detailed information about preparing your perennials for winter.