Plant Hardiness in the Landscape

All of us have recently been made aware of how much the outside temperatures can fluctuate during the late fall/ winter season.  Woody plants are able to survive freezing temperatures because of the metabolic changes that happen within the plant with the changing of the seasons.  You have heard terms such as cold hardy, frost hardy and winter hardy.  They are used to describe woody plants that can survive freezing temperatures without being injured during their winter dormancy period.

According to Elton Smith and Mary Ann Rose of Ohio State University (see HTG-1016-96) the genetic capacity of a plant to getting acclimated to freezing temperatures determines its cold hardiness.  The cold hardiness of a species is usually considered to be the lowest midwinter temperature that the plants tissues can take.  Sometimes injury occurs during the fall or spring when the plant is not at its maximum hardiness.  Many plants develop their hardiness to freezing temperatures in response to changes in the amount or duration of light they receive and temperature.  The shortened hours of daylight in the fall starts the hardening process by slowing the vegetative growth.  Cool temperatures initiate the accumulation of sugars and changes in cell membrane permeability.

Causes of winter injury to trees and shrubs are brought on by extreme cold, drying winds, bright sunlight or a sudden drop in temperature.  How much winter damage a plant will experience is determined by a number of factors which include the plant species or cultivar, the location and under what conditions the plant is grown in and the weather extremes that occur during the plants period of dormancy.

Winter hardiness is an important factor to consider when choosing landscape plants.  Always plant cultivars that are hardy in your area.  Checking the plant description tag along with some investigative work on the internet will provide you with the proper hardiness zone and planting instructions for that particular plant.  Proper location, exposure, soil type, protection/screening and mulching are important things to keep in mind in care and maintenance.

The very cold winters of 2014 and 2015 points out the importance of considering hardiness zones when purchasing landscape plants.  There are some people of the gardening population that want what they can’t have and therefore have a tendency to purchase plants that are rated a zone warmer than what they live in.  These people are referred to as “zone pushers” (you know who you are)!  Many out of zone plants can and have survived our “mild” winters, however, the winters of 2014 and 2015 put an end to  many “zone pushers” dream plants.  Sticking to plants that are rated for your zone will reduce the potential for major disappointment in the future.

The USDA Hardiness Zone website has a “Find Your Zone” search that will identify your hardiness zone based on your zip code.

If winter damage does occur there are some things that can be done to prevent permanent damage.  Once the threat of a late spring freeze is over remove any dead or damaged branches. Also in the spring, spread a fertilizer, such as 10-6-4 on the ground under the drip-line so the rain can wash it into the roots.  Pay special attention to damaged plants throughout the growing season.  Water thoroughly during any dry periods.

As always, Happy Gardening!!

More information about gardening and related subjects is available online. The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 In Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.

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