A Greener View by Jeff Rugg

If you watched the weather reports from the last few weeks, you know it has been very cold in a lot of places that are supposed to be warm this time of year.

Plants are not all created the same. Plants native to areas near the equator are called tropical plants. As a group, they don't do well if the temperature drops into the 50s. Subtropical plants, which are native to areas closer to the poles and at higher altitudes than tropical plants, can often survive a frost. Temperate plants are native to lands that are always exposed to frost or freezing temperatures.

All cold weather is not created the same, either. Each time it occurs, the cold air mass has a different size, direction, humidity, wind speed and lingers for a different amount of time. The same cold system in November would cause a lot more damage to plants than in January, since plants wouldn't be "prepared" or acclimated for the earlier storm. Temperate and subtropical plants exposed to shorter days and cooler temperatures adjust by developing more antifreeze.

Every individual landscape has microclimates that cool off slower and warm up quicker — the total below freezing time is less in some parts of the landscape. The sun warms south-facing walls, and trees, even with bare branches, trap warmth released from the ground, which keeps areas near buildings and under trees slightly warmer.

All of these differences mean that each time there is a cold spell, the exposed plants are going to react differently. A temperature of 25 degrees in one cold spell may kill plants that survived an earlier 20 degree cold spell. A plant in the shelter of a building may survive the night that kills the same kind of plant farther from the warmer microclimate.

Brown and dead leaves is the first symptom that is going to show up on cold-damaged plants. Lawns and evergreen shrubs will show symptoms first.

Plants without leaves will have bark and bud damage that won't be visible for a few days to a few weeks. Test scratching just under the bark should show green tissue, not brown tissue.

The preferred treatment for frost-damaged plants is to just leave everything alone until spring. Dead leaves doesn't always mean a dead plant. Don't try to force growth by fertilizing or watering. There may still be more cold weather coming that would damage a plant that is trying to grow. Pruning should only be done on plants that have started growing again, so live wood can be determined.

Covering plants works best if the waterproof cover goes all the way to the ground, doesn't touch any leaves and can insulate the plants. A blanket and plastic work better than either alone. Covering works better for a frosty night, not against a cold weather system lasting for days. When plastic touches leaves, it transfers heat and allows the leaves to freeze.

A palm cannot replace its trunk's water-conducting cells that have been damaged by frost. A frozen palm may look fine until all the water in the trunk is consumed; it will then suddenly wilt and die. The central growing point of a palm tree already has its next spring's leaves. If they are damaged by the cold, they will come out distorted and brown and may need to be pruned at that point.

While seeds may be strong, flowers and fruit are the most frost-tender parts of almost every plant. This is why the citrus trees survive, but the fruit does not. Leaves are often expendable, even on broadleaved evergreens like hollies, palms and rhododendrons.

Cold-damaged plants will be more susceptible to disease in the spring. You may need to have a certified arborist look at any trees you think are having problems. Fungicide and fertilizer treatments may be necessary to restore health to freeze-damaged trees.

E-mail questions to Jeff Rugg, University of Illinois Extension at jrugg@illinois.edu. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

COPYRIGHT 2010 CREATORS.COM

??

??

??

??