What is Allelopathy?

Allelopathy is when plants secrete a biochemical which keeps other plants from growing near them. These biochemical materials are called allelochemicals. These allelochemicals inhibit the germination of other plants around them. They affect the physiological processes of the plants such as respiration, cell division, and water and nutrient uptake. Symptoms include leaf yellowing and wilting or part of the plant will die. The allelochemicals can be found in leaves, roots, flowers, fruits or stems and in the surrounding soil.

Allelopathy is the plants way to compete with other plants for the available resources just like animals do in claiming their territory. Plants are competing for sunlight, water and nutrients with other plants and by secreting the allelochemicals into the soil the plant gets rid of its competition and controls its environment.

There are a lot of allelopathic plants. Salt cedars, sugar maple, hackberry, eucalyptus, black walnut, juniper, sycamore, oaks and balsam poplar are all allelopathic. There are a variety of chemicals these plants use, some use phenols, coumarins, juglone and terpenoides to name a few. An unusual aspect is that some alleopathic plants discriminate and release more chemicals on specific plants. Most of the chemicals are released through the soil and the amounts of chemicals that accumulate are dependent on how well the soil drains. Clay soils don’t drain well so the chemicals really build up in clay soil.

Most things in life have a positive and a negative side and there are some positives to allelopathic plants. Scientists are studying the chemicals in these plants for their potential use as natural pesticides and weed killers. Studies on the possibilities of using allelopathic chemicals to slow the growth or contain the growth of trees are being conducted which would be especially helpful for trees near power lines which require regular pruning by tree care specialists. Allelopathic plants can also be used for weed control for agriculture.

There really isn’t a way to stop the effects of the allelopathic plants on the plants they affect. The best strategy is to not plant anything near them that will be hurt by the chemicals. Salt cedars, for example, will affect any plant near them. Other allelopathic plants will affect only certain plants near them. One of the best known allelopathic plants is the black walnut tree which can be a tall, majestic tree. You won’t see any vegetation growing under black walnuts because they release a powerful allelopathic chemical called juglone. However, there are some trees that can be successfully grown near black walnuts like serviceberry or arborvitae.

About the Author: Andrew Johnson is the owner of Central Texas Tree Care, a leading tree service provider in Central Texas (Travis County and surrounding areas) offering services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management, fertilization and Austin tree service trusts. For more information please visit http://www.centraltexastreecare.com.