Express-News

Saturday, November 29, 2003

By Calvin Finch, Conservation Director, SAWS, and Horticulturist

 

Questions and Answers on Freeze Damage

 

Q.        Does it make any difference if you water your plants just before the freeze arrives?

 

A.        In most cases, no.  The idea of watering just before the freeze is based on some legitimate relationships between freeze damage and water but is not effective in itself.

 

·        A well-watered healthy plant or lawn can withstand cold weather better than a stressed plant.  The watering, however, needs to occur on a regular basis to keep the plant healthy, not just before the freeze.

 

·        Water applied with a sprinkler to a plant such as a peach tree during the entire period of freezing temperatures will keep the foliage and fruit at 32 degrees F.  The key is to keep the sprinkler on the tree the entire time.  A 10-minute or even 1-hour splashing will not do it.

 

·        Water does moderate temperatures on the coast and near large lakes because of the high amount of energy required to change the temperature of water.  A few gallons added to the soil, however, does not have much impact.

 

Q.        Will my tomatoes ripen and taste just as good as vine-ripened fruit if I pull them all off just before the freeze?

 

A.             Tomatoes are physiologically mature when they make a color change from dark green to light green.  That means they will turn red and taste pretty good if they are picked at that stage.  I can say that they taste just as good, but no one will believe me.  Taste is a subjective thing, and most people believe a vine-ripened tomato tastes better than a fruit that is picked early and allowed to ripen in the kitchen or in transit.  Even if there is some difference in taste, they are still great.

 

Q.        Why would I want to wait before I cut down freeze-damaged foliage such as lantana or rose?

 

A.        There are several reasons to wait to cut down root-hardy perennials such as lantana, esperanza, and poinciana, but it is not life threatening to the plant.  Often a freeze will defoliate the plant but not kill the stems.  If you leave the stems and they survive the winter, the plant does not have to start from the roots and will be larger.  A second more esoteric reason is that birds use the plant material for shelter and hunt for seeds and insects in the tangle.

For hardy plants like roses, figs, or citrus the danger in pruning off the damaged portions too early is that the open wounds are more susceptible to further freeze damage than are the uncut stems.  In some cases, the pruning may also stimulate new growth so early in the season that it is especially prone to further damage.

 

Q.        Why isn’t plastic as good as fabric in preventing freeze damage?

 

A.        Plastic mounted on a frame and kept off the foliage is effective in keeping warm air within the plant crown.  The problem comes when foliage touches the plastic.  Plastic does not block the heat transfer when there is no insulating layer of air.  Plastic is more like metal in conducting heat from solid to solid.  A combination of cloth and plastic is very effective, especially if there is wind or moisture.

 

Q.        What determines how much damage occurs when a plant is subjected to a freeze?

 

A.        This is a complex issue.  The temperature and duration of temperatures below freezing are key factors.  Plant genetics is also important.  Tropical plants have an arrangement of molecules and chemical reactions that are completely disrupted by cold temperatures.  Hardy plants reorganize their chemistry every year when cold weather approaches.  Structure and chemical reactions to utilize nutrients, light, and water for growth are replaced with chemistry arranged to tolerate or resist freezing temperatures.

Another factor is the speed with which temperatures change.  Many plants can tolerate very cold weather if the temperature drops slowly but are damaged severely by low temperatures that arrive before the plant has properly “hardened off” or arrive in the spring after the plant has moved from dormancy to growth mode.  In mid winter, after a cool autumn, many plants can tolerate severe temperatures, but the same temperatures will kill the plant in late spring or early autumn.