WICHE: Drought, heat cause stress to trees, shrubs

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Be careful with how you treat them

By Jeneen Wiche

“Newly transplanted trees must remain hydrated in order for the natural process of root system regeneration to begin” writes Roger Harris, associate professor of horticulture at Virginia Polytechnic Institute.

This is something that has been repeated countless time this summer by many in the green industry, yet, I fear, some homeowners may have turned a deaf ear.

With record-breaking heat and drought conditions for many in Kentuckiana, plants suffer the most if their caregiver is less than committed! Do not be perplexed over the death of landscape plants now or next year if you got lazy with your watering chores during the heat and drought of 2012.

And if you have received rain left over from Hurricane Isaac, do not think you are completely off the hook with the newly planted. Freshly turned soil dries out faster, and new plants have yet to establish their roots. There is also the stress of simply leaving a pot, have your roots fondled and being planted. Water is the key to success.

Turf grass will rebound, no doubt about that, but the stress caused by drought and excessive heat can have some long-term effects, especially for those plants that already are stressed from some other ailment or environmental condition.

Drought conditions alone generally will not kill older, established trees. It is usually a combination of factors. Combine drought conditions with trees already suffering from “lawn mower” blight (trunk injuries from lawn equipment), old sun scald scars (where the cambium layer has died) or girdled roots, or environmental problems like poor drainage, compacted soil or pollution. and trees are more susceptible to total kill during and after a period of prolonged drought.

It is a vicious cycle: One type of stress leaves the tree vulnerable to another type of stress. If you look at it in terms of human health, you can see a pattern: Malnourishment or a weakened immune system leaves us vulnerable to other forms of illness.

On the other hand, newly planted trees and shrubs certainly will perish if they have not been watered.

Newly planted trees spend their first year trying to reestablish a root system. In their second year they store up energy; and in their third year they will start to put on some noticeable new growth. Here, again, the key is moisture.

Homeowners with newly planted landscapes only can blame themselves for the decline of their plants if they have not irrigated. You may be worn out from watering, but the chore is far from over, because drought stressed plant material will enter into the winter months at a disadvantage and thus be susceptible to cold-related damage.

Next spring, tip dieback may be more evident. Keep an eye out for long-term effects like canker disease, which usually shows up the season after a drought. You will see areas that have cracked and split open in bands around the trunk. The cambium layer beneath the bark will die, and the tree will be unable to transport nutrients effectively to the tissue above the diseased area.

Evergreens are particularly susceptible to winter injury after a drought. All trees transpire moisture through their leaves, and because evergreens hold their leaves throughout the winter months, this means that they continue to lose moisture. Evergreens are especially susceptible to winter dieback and burned foliage after a season of drought.

The most depressing thing that you may see next spring is a seemingly healthy tree leaf out and bloom and then die overnight. Basically the tree uses up the last bit of life it has in it to break dormancy. I suppose it is a good way to go if you are a tree.

As we head into late summer, continue to water plant material that has shown signs of stress. Slow, deep irrigation every two weeks is much better then frequent watering. However, newly planted trees and shrubs may need hand watering every couple of days to keep from drying out completely.

Remove any diseased or dead wood to eliminate safe harbors for insects. Fertilize with some composted manure as mulch or some other nitrogen source (like cottonseed meal) in late November.

If you use synthetic nitrogen, wait until the tree has gone dormant, because you will encourage new growth that will stress the plant even more. Do not fertilize new plantings from this year. Wait until next fall.


Check out gardening columnist Jeneen Wiche’s work at www.SwallowRailFarm.com. You can find her columns also at www.SentinelNews.com/agriculture. She answers questions once a month in SentinelNewsPlus. To submit a question, send an E-mail to jwiche@shelbybb.net and type “Sentinel-News” in the subject field.