Allelopathic Plants: Lone Killers
These Plants Compete Chemically with Other Plants
Allelopathic plants don’t want any other plants near them. In fact, like Greta Garbo, they just want to be alone.
But what plants are allelopathic and how do they affect other plants? Are their chemical attacks specific to one genus, or are they indiscriminate? What are the chemicals they use?
There are many allelopathic plants. Some discriminate, and have a stronger effect on specific plants. Others are indiscriminate. They use a variety of chemicals. Some use phenols. Others use coumarins. Plants also use juglone, cyanogenic glycosides, and terpenoides.
These chemicals affect plants in different ways. Some act on the plant’s respiration, blocking it, and inhibiting the plant’s transfer of energy. Some slow plant growth, or stop cell division, thereby interfering with seed germination. Some allelopathic chemicals interfere with a plant’s ability to take in water and nutrients. In a few instances, the chemical can kill a plant, or prevent it from becoming established, or reduce plant growth.
Allelopathic plants spread their chemicals mainly through the soil (although some may also be absorbed directly from the air). How much chemicals accumulate there depends on how well the soil drains, how much aeration there is in the soil, temperature and a number of other factors.
Chemicals accumulate in clay soils, because clay soils do not drain well. In sandy soils, however, they leach out quickly. So if you’re planting near allelopathic plants, don’t put plants sensitive to the chemicals in heavy clay soils.
Also, microorganisms may break down allelopathic chemicals.
Here are some examples of plants that are allelopathic and some of the plants they affect:
Salt Cedars
- Almost every other plant
Sugar maple
- Yellow Birch
- White spruce
Hackberry
- Herbs
- Grasses
Eucalyptus
- Shrubs
- Herbs
- Grasses
Black Walnut
- Pines
- Apple
- Birch
- Black Alder
- Hackberry
- Basswood
- Azalea
Juniper
- Grasses
Sycamore
- Yellow Birch
- Herbs
- Grasses
Oaks
- Red Maple
- Red Pine
Sassafras
- Elm
- Silver Maple
- Box elder
Balsam poplar
- Green Alder
- Southern red oak
- Sweet gum
Laurel
- Black Spruce
Manzanita
- Herbs
- Grasses
Bearberry
- Pine
- Spruce
- Sumac
- Douglas fir
Elderberry
- Douglas fir
Forsythia intermedia
- Kentucky bluegrass
- Goldenrod
- Sugar Maple
- Bl. Cherry
- Tulip Poplar
- Red Pine
Despite the negative effects of allelopathic plants, there are some positive aspects too.
Agriculturalists and scientists are now looking at the chemicals in allelopathic plants for their possibilities as natural pesticides and natural weed killers.
Costs of pruning trees are considerable, especially those trees that are growing up around power lines. Studies are being conducted on the possibilities of using allelopathic chemicals, which inhibit growth to slow or contain the growth of trees along those lines.
Planting cover crops of allelopathic vegetation can lower weed infestation and lower or eliminate use of herbicides.
At this time, there are no ways to reduce the effect of allelopathic vegetation on the plants they affect. The best solution is to put susceptible plants far enough away from allelopathic plants so they won’t be affected.
