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Down the Garden Path

Plants Coping with the Weather

Plants have had quite a time dealing with the very cold weather and blustery winter winds. The lucky ones are currently under the snow and well protected. Soil temperatures remain constant and while covered by the snow, temperatures around the stems, twigs, foliage or buds are protected from the dry cold winter winds.

One of our best defenses against winter damage is making sure our plants have the correct winter hardiness. Our part of Illinois is in zone 5b covering winter temperatures between -10 and -15 degrees in a typical winter. Plants with a higher rating (above 6a) will show winter damage if they survive. This information is on the plant tag. The zones have changed, so be sure the information includes the actual temperature range to be sure. Another part of this winter hardiness is that of the root system itself. Roots are normally kept warmer than the above ground parts due to the insulating nature of the soil. In very cold winters where the soil can become colder than normal, there can be damage to the root system as well. A plant that would normally survive our winters grown in a container may not do well because the roots will have been exposed to the much colder air temperatures when the soil in the container freezes solid. When a plant is planted to shallow, the surface roots can be damaged in the same way.

When buds and stems are exposed to cold temperatures and winter winds over time, moisture is lost and tip and stem dieback are common. Evergreen needles no longer containing enough moisture, will brown as spring arrives with warmer temperatures. To ensure that water loss is kept down, watering the needle evergreens and broadleaved plants very late in the season before the ground freezes really helps.

Broadleaved plants like Rhododendrons, Azaleas and Boxwood will show different signs, but all caused by the winter temperatures and wind desiccation. Rhododendrons will cup or curl their leaves and turn a dark reddish brown during these very cold conditions. Some leaf loss should be expected, yet most of the leaves should return to normal in the spring and again be that deep dark green we expect. Rhododendron flower buds may not be so lucky and either the flower buds upon with damage or do not open at all and fall off as spring progresses. Boxwood leaves will turn a very pale color and those leaves are usually lost as newer leaves appear.

Home Orchardists will see a loss of peach flower buds, while the vegetative buds remain viable. Flower buds begin to be damaged at temperatures below zero and by minus ten degrees buds are killed. The more days we have in this range the more flower buds are killed.

All this snow we have had have also left trees, shrubs and evergreens buried or with branches bent over. It is best to let these recover on their own, as attempting to remove the snow will harm the plants more than leaving them alone.