The Greener View: Cold Weather
If you don't live in the West Coast or southern Florida, you probably experienced some record cold temperatures last week. It was very cold in a lot of places that are supposed to be warm this time of year.
Plants are not all created equal. 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 are native to areas closer to the poles and at higher altitudes than tropical plants and can often survive a frost. Temperate plants are native to lands that always expose them to frost or freezing.
All cold weather is not the same, either. Each time it occurs, the cold air mass lingers for a different amount of time and has a different size, direction, humidity and wind speed. The exact same cold system in November causes a lot more damage to plants than in January because plants are not prepared for or acclimated to the harsh November weather.
Temperate and subtropical plants exposed to shorter days and cooler temperatures develop more antifreeze that helps them survive cold weather. This process takes time, and some plants may not have been entirely ready for last week's cold.
Every individual landscape has microclimates that cool off slower and warm up quicker, so the total amount of time that the temperature is below freezing is less in certain parts of the landscape. The sun warms south-facing walls, and trees trap warmth released from the ground, even when the branches are bare, keeping areas near buildings and under trees slightly warmer.
All of these differences mean that each time there is a cold spell, the plants exposed to the cold are going to react differently. A temperature of 25 F in one cold spell may kill plants that survived an earlier 20 F cold spell. A plant in the shelter of a building may survive the night that kills the same kind of plant farther from the building's warmer microclimate.
The first symptom that is going to show up on cold, damaged plants is dead, brown leaves. Lawns and evergreen shrubs often show symptoms first. Plants without leaves will have bark and bud damage that won't be visible for a few days or weeks. Scratching just under the bark should show green tissue, not brown.
The preferred treatment of frost-damaged plants is to leave them alone until spring. Dead leaves don't always mean a dead plant. Don't try to force growth by fertilizing or watering. There may be more cold weather coming that would damage a plant that is trying to grow new leaves. Pruning should only be done on plants that have begun growing again, when live wood can be determined.
Covering plants works best if the cover is waterproof, goes all the way to the ground, doesn't touch any leaves and insulates the plants. A blanket and plastic work better than either alone. Covering works best for a frosty night, not a cold weather system lasting for days. Plastic touching leaves transfers heat and allows the leaves to freeze.
Palms cannot replace freeze-damaged, water-conducting cells in the trunk like other plants. A frozen palm may look fine until all the water in the trunk is consumed, and then it will suddenly wilt and die. The central growing point of a palm tree already has 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, which 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.
On the bright side, many insect pests were also probably not prepared for the cold, and there may be fewer pests in the spring.
Email questions to Jeff Rugg at firstname.lastname@example.org. 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.