What does that mean?
Patty called last week and asked if Eucalyptus were allelopathic (al-le-lop-a-th-ic). “Are what?” She quickly explained what it meant. I Googled to find the answer and yes, they are. Of course that lead me down the research road and to this article. Allelopathy comes from the Greek “allelo” and “pathy” meaning “mutual suffering” or “to suffer from each other”. In simple words allelopathic plants hate company. They are capable of making their immediate surroundings unfavorable to competition, effectively clearing the way, for their own benefit. Why share valuable resources like light, water and nutrients when you can have those things to yourself? Without competition, plants can grow bigger and stronger, potentially reproducing and taking over their “world”. It’s one of those “survival of the fittest” things, that decides whether a species will be successful or fade from existence.
Allelopathic plants use sophisticated chemicals to protect their space from invaders. If some of these chemicals could be bottled up and available to us, we might feel better about the “weed killers” we use. The chemicals can be from the roots, leaves and the stems of these unfriendly plants. Because of our mostly clay soils, these chemicals can become concentrated and their effects are magnified. Some plants emit chemicals that attack another’s DNA or ability to absorb water. Still others inhibit the photosynthesis of their neighbors. Allelopathy is not a commonly studied science and is still in its infancy, we mostly depend on observation and trial and error. Accounts go back to Greece in 300 BC. The “Father of Botany”, Theophrastus, noted his observations about how chickpeas, killed off weeds. Most of us have heard of companion planting. This is a sort of allelopathy. Certain plants seem to help others, while some combinations are fatal to one of the participants.
Get out of my room! (if you have a teen, you know the voice to use)
Some plants don’t use chemicals to get their way. Aggressively growing and crowding the neighbors out works too. Think about kudzu, its motto is “If you won’t make room for me, then I’ll just grow over you”. This ties in closely to the rules about spacing plants correctly. Correct spacing reduces the demand on resources, giving every plant an equal chance at survival. If you’re an “immediate gratification” person, you will learn that with plants, more is not always better. Landscapers that over plant, crowding things in so it looks “full”, aren’t doing you or the plants a favor. It’s sort of like trying to raise 12 kids in a 3 bedroom/1 bath house, you may get the job done, but there will be suffering, resentment and fighting. Plants, like kids, need space to grow.
No wonder the grass won’t grow
Ever have a spot where nothing you plant grows? It may be an allelopathic situation. Probably the best known “killer” plant, in these parts, are pecans. Some of the most common allelopathic trees are Sycamore, Cottonwood (no great loss there), Red Oak, junipers, Sassafras, Black Walnut, eucalyptus, bottlebrush, Wax Myrtle and avocado. We recommend just mulch under them and learn to love it. Ever notice that the ground under your bird feeder stays bare? Sunflowers and their seeds inhibit plant growth. Tobacco, rice, peas, corn, and sorghum all have allelopathic properties. Kentucky Blue grass (yeah, I know it doesn’t grow here) will kill azaleas.
What to do
Mulch and rocks (big ones) are a creative answer, giving the illusion that you didn’t plant it, on purpose. How about a small paved area or path…use natural stone in an informal pattern. Maybe add a bench, glider or a bird bath. Perhaps a hammock is more your style. How about a fairy garden? Maybe a teepee for the kids to play in. Always wanted a bacce court? Voila, a problem area becomes a focal point instead of an eye sore.