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Archive for Thursday, April 12, 2007

Damage to plants still unpredictable

April 12, 2007

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For years, meteorologists have reported the average high and low temperatures, normal rainfall amounts and other statistics for any given day. But, just once, I would like to experience a "normal" season in Kansas. Maybe it's me; maybe 80 degrees one day and 20 degrees the next IS normal. But try telling that to our landscape plants, many of which were either fully leafed out or well on their way to being so. Now that the temperatures have dropped well below the magical 28 degrees, what should gardeners and landscape professionals be doing to pick up the pieces? In a nutshell, not much. Here's why.

This time of year, temperatures are an important influence on plant growth and development. Extreme temperature fluctuations are common and can cause a whole host of problems. Leaf damage or death, flower death, twig or branch die-back are just a few. Unfortunately, the ensuing damage is both variable and unpredictable. Plant growth characteristics, overall plant health, soil, water availability, stage of development or dormancy, and microclimates all play a role in plant hardiness.

But since the temperatures fell into the teens recently, examine plants over the next few days and expect to find leaves or flowers that have become brown, black and/or mushy. However, on larger trees and shrubs, damage may not show up immediately. Watch the plant during the remainder of spring. If leaves are not sprouting and the wood appears dead, check the layer of tissue directly under the bark for discoloration. If that layer is black or brown, prune it back. Wait until late spring before pruning because it stimulates new growth that would be more susceptible to cold damage the following weeks.

Following is a short list of what you can expect to find and what you should do as a result of the freezing cold temperatures:

l Trees and shrubs: Blooming flowers die. Some leaves may scorch or "burn" back. With temperatures in the teens, terminal shoots may freeze and die. However, even if all of the new growth dies, dormant buds will become active and new growth eventually will emerge.

l Herbaceous plants: Mulch or a blanket may have provided some protection, but not reliably. If the top growth froze, the plant will probably put out new growth starting from below-ground buds. In a few weeks, remove the dead tops or stems to make room for the emerging shoots.

l Vegetables: Plants that can withstand temperatures in the mid-20s without damage include asparagus, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, kale and turnips. Cool weather-tolerant plants that can take a light frost include Bibb lettuce, Chinese cabbage, collards, Irish potatoes, leaf lettuce, mustard greens, radishes, spinach and Swiss chard. Replant those plants that did not survive.

l Fruit trees: Extent of damage depends on stage of fruit development, as well as temperature. To check for bud damage, cut several twigs with fruit buds and bring them inside. Place the cut ends in water for 48 hours. Cut the buds longitudinally and look for browning injury on the floral parts. If the parts are brown or black, the embryo has frozen and the fruit crop is most likely gone. One exception to this is pears. These buds often exhibit browning in the buds and the vascular tissues, which does not necessarily mean they are dead. On blooming trees, look at the pistil or ovary and see if it is brown or withered. If so, the flower will not produce a fruit.

- Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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