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Index : Plant Problems - Cultural
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- 7. What to Do With Freeze Damaged Plants - Top
- Over the past month, we have experienced below freezing temperatures a total of 8 days! In one period from January 19 - 22, sub - freezing temperatures occurred 4 consecutive nights. In some parts of Tucson temperatures dropped as low as 20 degrees F. The result - lots of cold damaged plants! So what can be done to help those plants recover.
First, determine the extent of cold injury. On plants with woody stems - trees, shrubs, and vines, - use a knife to peal back some of the bark on stems with frozen leaves. If you find moist, green sapwood just underneath the bark, that stem is still alive. Live stems, even leafless ones, will regenerate leaves when the temperatures warm consistently.
Only cut off stems which have been killed by the cold. These will have sapwood that is dry and brown when you peal back the bark. Cut dead stems all the way back to live wood. The amount you cut will vary greatly depending on the plant. For instance; lantana may have frozen back to within a few inches of the ground, making it necessary to cut the stems back severely. Other plants, such as bougainvillea and citrus may have very little injury to the stems, requiring little or no pruning back.
Some plants may have frozen leaves still attached to the stems. For these plants, delay any pruning a few more weeks. The dead leaves provide some insulation to the healthy leaves and stems below. If we do have another cold snap, these dead leaves will hold in some warmth and help protect the plant from further damage. By mid-March all danger of frost should be behind us and pruning of these plants can commence.
If your unsure about where to cut, wait until new growth emerges in March. This will tell you exactly where the dead parts met the living. Simply remove everything back to where the new growth is sprouting out.
Flowers and other herbaceous plants injured by the cold need attention without delay. Geraniums, impatiens, begonias, aloes and other soft-stemmed plants should have any frozen and wilted stems removed. Cut them off cleanly with a sharp sizzors or hand pruners. Old, faded and frozen flowers should also be removed. Apply a liquid fertilizer to flowers and herbs to speed their recovery.
Wait to fertilize cold-injured trees, shrubs and vines for a few more weeks. Fertilizing now could stimulate new growth that is vulnerable to further cold injury, should the occasion arise. The exception is citrus, which should be fertilized in February to encourage spring flowering and the resulting fruit set.
Make sure all freeze-damaged plants have adequate moisture. Injured leaves and stems will loose more moisture through their wounds than undamaged ones. Keep the soil moist, but not overly wet. You don't want to water-log plants! Using a simple moisture meter available at garden stores will help. Soft stemmed, herbaceous flowers and herbs will be most vulnerable to drying effects of cold damage, so check them often.
Watering will also help eliminate any excess salts that might be in the soil. Salts can cause additional damage to plants over and above the effects of cold. The best way to eliminate excess salt is by leaching them out. For container plants, simply moisten the soil to dissolve the salts. Wait an hour or so. Then come back and hand-water the containers until water runs freely out the drainage holes. This will wash the dissolved salts right out the bottom of the pot.
Use the same process for plants in the ground. Water as you would normally, then wait a few hours and water again. Apply lots of water, the excess will push the salts down below the root zone and away from your plants.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: February 17, 2002
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