Article updated January 30, 2023
As wintry weather whips us with cold temps, chilly wind and freezing precipitation, we can withstand the season with heated homes, hot beverages and puffer jackets. Our trees, shrubs and perennials, however, just have to stand there and take it.
There are several steps you can take, however, to give your outdoor plants some TLC during winter to help ensure that their health—and your investment—are well-protected come spring.
We spoke with Leonard Filchner, owner of Filchner’s Plants & Produce in Bath, Pa., (Plant Hardiness Zone 6b) for expert tips on how to keep outdoor plants alive in winter in the general Northeastern area of the United States.
When to Fertilize to Keep Outdoor Plants Alive in Winter
According to Filchner, you should stop fertiziling your perennials, shrubs and trees in August–September to keep outdoor plants alive in winter. Once the season changes from summer to fall, bringing with it less sunlight and cooler temperatures, outdoor plants will naturally start to go dormant, conserving their energy for when spring returns.
If you continue to fertilize during this time, you’ll force your plants to push out tender, new growth, which will be like “leaving your plants out in winter without a coat on,” says Filchner. Your outdoor plants won’t be able to properly acclimate to the incoming winter weather, which will make them vulnerable to damage and can ultimately kill them.
How to Mulch to Keep Outdoor Plants Alive in Winter
It’s a good idea to spread about two to three inches of mulch in a wide, even layer around your outdoor plants to keep them alive in winter, says Filchner. The mulch, by shielding the soil from the warmth of the sun, keeps the ground cold. A steady cold temperature will keep your plants in dormancy and prevent them from triggering new growth in the event of a warm spell. The mulch in turn also acts like a blanket, keeping the cold from penetrating too far into the soil where it can damage a plant’s roots.
Winter mulching also prevents frost heave to keep outdoor plants alive in winter. Frost heave is when soil freezes and then thaws, which can crack the soil, exposing the roots of a plant to the cold air above. In severe cases, frost heave can actually lift (heave) plants out of the soil. Either way, exposing a plant’s roots to frost can kill the plant, even if the rest of the plant can stand a bit of frost.
For crops such as strawberries, Filchner recommends covering them with straw in winter, which protects both the roots and the foliage. However, it’s important to remove the straw around early April when the temperature starts to rise. If the straw isn’t removed, the plants will try to push up once they feel more warmth from the sun, but without exposure to it, the plants will weaken.
Should You Water to Keep Plants Alive in Winter?
Some gardeners suggest watering outdoor plants a few days before an expected frost or freeze to keep outdoor plants alive in winter. However, Filchner recommends against it. “Plants don’t use as much water in the winter,” says Filchner. “The rain and snow you get during the season should be enough moisture for your outdoor plants to stay alive.”
One of the main reasons not to water to keep outdoor plants alive in winter is to avoid the risk of having ice form inside of a plant’s cells, which can cause the cells to burst. According to The Old Farmer’s Almanac, plants prepare for winter by moving water from their cells outside the cell walls where it can freeze safely. As the ice thaws, water can then be reabsorbed by the cells to prevent dehydration. Plants also make excess sugars during the summer and concentrate them in their cells to act like a form of antifreeze in the winter months. Watering to keep outdoor plants alive in winter has the potential to disrupt this natural process.
How to Add Protection to Keep Outdoor Plants Alive in Winter
Protecting your outdoor plants by tying them up with jute twine, or covering them with A-Frames or plant tents, are other ways to keep outdoor plants alive in winter.
Valuable plants such as rhododendrons and roses can also be tied up to make them more compact, packed by fallen leaves for insulation and then wrapped in burlap stapled to wooden stakes surrounding the plant. Keep in mind, however, that this method can attract mice and other rodents looking for a warm place to tuck in and eat during the winter, says Filchner. Also, as the fallen leaves get wet, they can rot around your plants.
Filchner recommends a product called Wilt-Pruf®, an organic and biodegradable, horticultural antitranspirant to protect valuable plants such as holly, laurel and magnolia from winter burn and other forms of water stress. Wilt-Pruf® sprays on as a clear, protective coating to prevent water loss in a plant’s leaves. (Wilt-Pruf® can also be used to extend the life of your live Christmas trees and wreaths.)
One additional and very important tip is to try only to install plants that are truly hardy enough to survive the winter weather in your area.
Now that you have several tips on how to keep outdoor plants alive in winter, you can look forward to tending to them again and enjoying their beauty and bounty in the growing season ahead. Remember to turn to Swan in spring for all of your watering needs. Here are three of our garden hose collections you might be interested in:
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