Harsh winters often take their toll on many tender plants. Frost is the main killer, but constant exposure to sub-zero temperatures can also damage all but the hardiest of plants. However, the gardener can do some things to help them survive the winter.
Broadleaf evergreens like rhododendrons, camellia shrubs, boxwood, and holly are able to survive low temperature conditions, but during the daytime, windburn and sunburn can cause damage. They can literally die of dehydration because their roots are not able to absorb water from the frozen soil, while their leaves continue to transpire water during the day.
Location is the best way to minimize damage to broadleaf evergreens during winter. Don’t plant them in areas where bright sun in early morning is liable to strike their leaves. The heat from the sun can rupture the plant tissues frozen from the night before.
Mulches can keep soil from freezing, but can also behave as insulators and therefore increase the risk of frost. With the temperature becoming more constant due to the mulch, any sudden drops in temperature during a frost can have a more severe effect on the plants. But, mulches if applied completely over the sensitive plant parts can prevent freeze damage.
Low ground cover plants can also act like mulches and therefore are useful in these regard. Evergreen boughs can be planted in the ground as a kind of palisade around the plants. They are able to trap some heat within these microclimate conditions.
If the location cannot be modified, you can install a small shelter constructed of plywood, cardboard, or styrofoam on the windward side. These materials have an insulating effect against the cold. These covers should be removed during the day as the air humidity underneath them would be higher and may be conducive to certain plant diseases.
Another method of preventing freeze damage is through the use of sprinklers. Low intensity sprinkling can prevent freeze damage due to the release of heat during cooling and freezing. But this method can only be effective if begun at the beginning of freezing conditions and sustained until the severe conditions have lifted. If the sprinkling is stopped halfway, it will actually be more damaging for the plants because the water droplets will freeze on the surface of the leaves. The use of sprinklers can only work if the frost conditions are not too long in duration.
Of course, a greenhouse solves all these winter problems easily, and you don’t even need an elaborate setup to begin with, if you just want to winter plants that would not survive the outdoor winter temperatures. Mini portable greenhouses are growing in popularity, and can be used as convenient temporary winter refuges for tender plants or seedlings.
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