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. This is why many houseplants that have been out for the summer die when brought back into the house late in the fall; they have already been exposed to many cold days and nights.

Subtropical plants, which are native to areas closer to the poles and at higher altitudes than tropical plants, can often survive a light frost. Temperate plants are native to lands that are always exposed to frost or freezing temperatures.

Temperate plants have several ways to cope with the cold. Some die and expect their seeds to grow when the weather warms up. Some die down to the ground, where the soil and possibly snow cover will protect the roots or bulbs from bitter temperatures. Roots in pots exposed to very cold air are susceptible to injury. Woody plants prepare for winter by producing antifreeze materials, so water won't turn into ice and break open the cells.

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 producing more antifreeze.

Every individual landscape has microclimates that cool off slower and warm up quicker — the total of 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 a night that kills the same kind of plant farther from the warmer microclimate.

Brown and dead leaves is the first symptom that will appear on cold- damaged plants. Evergreen shrubs will show symptoms first. Plants without leaves will have bark and bud damage, which 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 freeze-damaged plants is to just leave everything alone until spring. Dead leaves doesn't always mean a dead plant. Pruning too soon may cut off live branches.

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

??

??

??

??