IT’S A HOMEGROWN TRADITION: When evergreens look ever-brown


IT’S A HOMEGROWN TRADITION: When evergreens look ever-brown

By AMY DISMUKES

Take a peek out your window, or walk down any street, and you’re likely to see an evergreen that appears more ‘ever brown.’

Is it some disease that’s wiping them out?

Nope, it’s the weather. This condition, often mistaken for a foliar disease, is actually a physiological disorder brought on by a combination of wind, sun and lack of available water.

evergreen
Weather-related injury on boxwood foliage. // AMY DISMUKES

While the drought of 2016 may be history for us, landscape plants may take years to fully recover, if they recover. Damage from drought can often show up months after the initial stress, specifically with evergreen plants (like laurel, boxwood, holly and assorted conifers, etc.). They give us few symptoms of water stress until it’s too late. Once past the permanent wilting point (aka point of no return), it’s pretty much over.

To make it just a little worse, when plants enter the winter in a ‘state of drought’, they’re at the mercy of nature, as winds pull any remaining moisture from the foliage. If already stressed, this pressure can be too much for the plant. The browning or bleaching of evergreen foliage during winter is a more serious condition and occurs for four main reasons:

Winter sun and wind cause excessive transpiration (foliage water loss) while the roots are in frozen soil and unable to replace lost water.

This results in desiccation and browning of the plant tissue.

Bright sunny days during the winter also cause warming of the tissue above ambient temperature which in turn initiates cellular activity. Then, when the sun is quickly shaded, foliage temperature drops to injurious levels and the foliage is injured or killed.

During bright, cold winter days, chlorophyll in the foliage is destroyed and is not resynthesized when temperatures are below 28° F. This results in a bleaching of the foliage.

Cold temperatures early in the fall before plants have hardened off completely or late spring after new growth has occurred can result in injury or death of this non-acclimated tissue.

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Browning of above-ground tissue associated with below ground root death

Evergreens will need special care this year. Those that were strong enough to survive the drought and the winter cold may exhibit some branch dieback from fungal
canker diseases. If your evergreens survived but are showing damage, wait until mid-spring to prune out injured foliage. Pruning out dead branches will limit future damage.

Never stress plants by under or overwatering. Decrease watering slightly in September to encourage hardening off, then water thoroughly in October until freeze-up. Watering only in late fall does not help reduce injury. Fertilize injured plants in early spring and water them well throughout the season. Rule of thumb during a drought: irrigate the keystone plants in your landscape (those that have significant aesthetic, economic or sentimental value) to ensure survival.

Be water wise, know the moisture needs of plants in your landscape and provide needed water when conditions call for it.

 

evergreensAmy Dismukes is the Horticulture Extension Agent for UT/ TSU Williamson County Extension. Amy is a graduate of Auburn University, where she received a Bachelor of Science in Horticulture: Sustainable Fruit and Vegetable Production and a Master of Agriculture in Plant Pathology & Entomology. She provides educational training for both homeowner and commercial clients about issues concerning horticulture and best management practices, coordinates the Williamson County Master Gardner Program and provides diagnostic services for Williamson County residents. Amy conducts both commercial and consumer site visits throughout the county to diagnose and resolve issues with insects, plant diseases, and weeds. Amy is a frequent guest speaker for professional, garden and horticultural associations, plant diagnostic training courses and commercial pesticide workshops and conferences. Amy is a member of and serves on the Board of Directors for the Tennessee Entomological Society, the Tennessee Urban Forestry Council and the Tennessee Association of Agriculture Agents & Specialists.

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