Monday, February 1, 2010

Managing cold damage

* 02/11/10: Another recent publication on cold damage - Click Here

After the cold snap over the holidays, there is a lot of concern about cold damage to plants in the landscape. To the left are pictures of a Dieffenbachia we left in our shadehouse before and after. As you can see, it didn't fair too well...

Just driving around the Redlands, widespread damage is apparent. A follow-up blog post about how to manage existing damage seemed timely, as many of you probably have questions about how to help your plants recover.

While damage done to foliage by cold temperatures is easy to spot because these leaves die and eventually drop off, the full extent of injury to trees and shrubs will not be evident until new growth begins.  

Dead foliage is unsightly, and the first instinct is to prune out all branches with dead foliage immediately. But it is better to wait until spring to do any heavy pruning because you can use the pattern of new growth to determine which parts of plants are still viable. Pruning too early can lead to cutting back branches that may recover, and leaving other branches that will continue to dieback. The best course of action is to delay pruning until new growth begins. In the meantime, dead leaves may be removed or left to fall off naturally. When pruning in the spring, make sure to make cuts into living tissue just behind where dead wood is present. You can tell where the boundary between dead and living tissue is by where new buds are growing, or you can scrape the bark gently with a knife. Live tissue is green where dead tissue is brown or black.

Watering/ Fertilizing
While watering right after a freeze can help warm the soil, overwatering may decrease oxygen levels and encourage root diseases. If leaf canopies have been severely reduced, water requirements will be lower. Careful monitoring of soil moisture and judicious irrigation will benefit the plant until the plants regrow their foliage. Depending on the host, fertilizing trees and shrubs right after a freeze may encourage the growth of suckers and water sprouts, which may make reshaping plants difficult.

If sever defoliation occurs, direct sun exposure can cause sunburn on exposed twigs and branches. Whitewashing affected bark can protect it until foliage returns. A water-diluted of white latex paint can be sprayed or painted on defoliated branches.

Disease management
As warmer weather returns, damaged areas of the plants are highly susceptible to fungal and bacterial pathogens. A preventative spray of a copper fungicide applied according to the manufacturer label may help protect damaged plants from diseases.

Managing cold damage in palms
Cold injury to palms often takes a long time to appear, from many months up to one year. Often only the bud remains alive, and damage to the trunk can restrict water movement for years to come. To assess the full damage to palms, monitor emerging leaves in the spring and summer. If they appear brown or deformed, this may indicate damage to the bud, which the tree usually grows out of as the season progresses. Damage to the trunk manifests as a sudden collapse of leaves during the first periods of warm weather, due to reduced capacity for water to reach those leaves. If severe trunk damage occurs, then death of the palm is inevitable. To manage diseases on damaged palms, prune leaves that are completely dead apply copper fungicide according to the product label. Applying foliar fertilizer to the leaves can help new growth and recovery of injured palms in the warmer season.

For more information on cold damage in palms see:

Managing cold damage to turf
Cold-damaged turf initially appears wilted and water-soaked, and eventually turns dark brown. Zoysiagrass and bermudagrass are more cold tolerant, while carpet grass and St. Augustinegrass are least tolerant to cold temperatures. Factors that contribute to cold damage include poor drainage, shade, close mowing height, excessive fertilization in the fall, and the buildup of thatch. Driving or walking on frozen turf will increase damage. Cold damage can resemble drought stress, and can lead to overwatering which in turn can encourage root stress and disease. Dormant turf needs less water, and so normal irrigation practices should be followed.

Further information on cold damage on turf can be found in:

Listed below are several other useful publication on cold damage to plants. You can also visit our last blog post about cold damage for further information, photos, and links to extension publications: