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Cold Weather Can Impact Landscape Plants
by Dr. William M. Johnson, Galveston County Extension Agent - Horticulture
Our winters tend to be relatively mild and that's considered a blessing by most folks. Nevertheless, temperatures can occasionally dip low enough to be able to inflict a significant toll on many landscape plants in the Galveston County area. However, homeowners can take protective measures to help reduce the occurrence of freeze injury to landscape and fruit plants if cold weather conditions occur.
Photo Credit: Herman Auer
As Im writing this weeks gardening column on the weekend, the temperature outside is sunny and pleasant. However, the weatherman is hinting that a cold snap may arrived in time for Christmas for the northern portion of the county.
Several scenarios are possible. The cold front will arrive but arrive later than predicted, the cold front will arrive and be worse than predicted, the cold front may fizzle out before getting to this areawell, you get the picture. So this weeks topic will be about cold protection for plants. Since the winter season officially started on December 21, it may be worthwhile to keep this article handy for future reference.
Several factors will influence the extent of cold injury damage to landscape trees and shrubs and even certain types of fruit, especially citrus. Such factors include variety (some may be more cold tolerant than others) and age (recent plantings that are not well-established are more susceptible to cold injury). A very important factor is the general health of a plant. Plants grown under low soil fertility or drought conditions or plants that suffered severe disease and/or insect problems during the summer growing season are far more likely to sustain damage.
However, homeowners can take protective measures to help reduce the occurrence of cold injury to landscape and fruit plants if cold weather conditions occur. These steps include the following:
PROVIDE INSULATING COVER TO PLANTS.Here are some things you already have around your house that can be used for just this purpose: paper bags, newspaper, flower pots, bath towels, beach towels, bed sheets, blankets, drop clothes, etc. (use your imagination!). Weigh them down with sticks and rocks or use clothes pins, twine and staplers to hold them in place. This can actually be funuse your creativity. Caution should be used when using plastic sheeting during prolonged hard freezes as plant leaves touching the plastic may suffer cold injury. However, it can be very beneficial to place plastic underneath blankets, sheets, etc. for large plants. The important thing to remember is to protect your plants from cold air circulation and hopefully youve already protected the plants roots by mulching in the fall.
KEEP PLANTS WELL-WATERED.Providing proper soil moisture conditions is an extremely important plant-saving practice for winter. It is very important that plants--those in the soil as well as those in containers--be provided adequate moisture throughout the winter season. The wind in the winter, like the sun in the summer, will dry soils. Be especially sure that soils are well-watered if a cold snap appears to be forthcoming to prevent plant roots from drying out. Freeze damage on plants can be significantly reduced or avoided if plants have adequate soil moisture before a severe cold snap occurs.
PROVIDE PROTECTION TO ROOTS AND CROWN.One of the most sensible ways to protect a plant from the effects of a severe freeze is to protect its roots and crown by mulching. Mulch is an excellent insulator. If the roots and crown survive, the plant can usually be salvaged and new top growth developed. Use mulches around annuals, perennial plantings, roses, etc. Clean straw, shredded pine bark, cottonseed hulls, compost, etc. make excellent mulches. In fact, most plants will benefit significantly if mulched throughout the year.
PROTECT LAWNS.Many homeowners lost large portions of their lawns after the December 1989 hard freeze when temperatures dipped as low as 7 degrees Fahrenheit. While most soils have good moisture thanks to the abundant rainfall over the last few weeks, be aware that maintaining adequate soil moisture throughout the winter in a lawn will enhance its level of tolerance to very cold temperatures. While bermudagrass is more cold tolerant than St. Augustine, be sure to keep either type of lawn well-watered (but not over-watered) even in winter, especially if temperatures appear likely to dip into the 20s or lower. Grass growing in the shade of large trees and on the north side of homes will likely sustain the greatest damage during a severe cold snap.
DELAY HEAVY PRUNING.In the event of a freeze, do not do any pruning until late winter or early spring even though affected woody plants may appear to be in poor condition. This applies to all citrus and ornamentals, including palm trees. Heavy pruning after a hard freeze can stimulate new growth which could easily be burned back if another cold snap occur. Also, it is easier to prune and shape ornamentals after the full extent of damage is known.
Some plants, of course, won't stand any freezing weather regardless of how many toughening techniques you employ. That's one of the many reasons for using only hardy plants in the basic framework of your landscape (such as for shade trees and screening and foundation plantings). Use the less hardy, more tender plants (i.e., flowering annuals, bougainvillea, hibiscus, etc.) as filler to add interest to entryways, flower beds or borders.
Take heed to the above steps and if a severe cold snap occurs, your plants will be in good shape.
(Information below is from the December 3, 2004 column.)
COLD INJURY ON PLANTS:Prepare landscape plants for possible severe cold snaps by taking a few preventive steps to help avoid injury. If you trust your weather prognosticator and he or she predicts a hard freeze and if your soil is on the dry side at the time, then be sure to water your plants well prior to the freeze. Odd as it may appear, many plants are killed due to a lack of sufficient soil moisture. Providing a 4-to-6 inch layer of mulch (such as leaves, compost, or shredded pine bark) will also help to reduce cold injury. While plastic does not provide sufficient protection to plants during a hard freeze, it can be used to protect cold-sensitive plants against light frosts. However, be very sure to remove the plastic immediately after the danger from a light frost has passed-temperatures inside a clear plastic covering can become very high on a sunny day.
TRANSPLANT TREES AND SHRUBS:December through February is an excellent time to transplant trees and shrubs. Transplanting during the winter season allows the root system of transplants to become better established prior to spring growth and summer heat. This significantly reduces plant stress during the following summer.
PLANT BULBS:Although Christmas is foremost on our minds right now, don't forget those tulip bulbs in the refrigerator as well as other types of bulbs requiring a chill treatment before planting (won't it be great to be able to reclaim that the refrigerator space). They should be planted in late December or by the first week in January after they have received 45-to-60 days of chilling. Tulip bulbs must be planted immediately upon removal from cold storage. Experimental evidence indicates that exposing bulbs to 10-to-14 days of room temperature (72 degrees F.) after removal from cold storage erases the benefits of cold storage.
PRUNING:Don't be in a hurry to prune woody plants. Very late December through early February is usually the best time to perform most winter pruning.
Dr. Johnson is a horticulturist with the Galveston County
League City Area News Online.
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