There is still so much to learn about the plants around us and how they interact with both us and other plants in their environment. One aspect of plants is just now getting some serious scientific study is the effects of allelopathy or the ability of one plant to inhibit another.
Toxicity is the degree that a substance can affect humans and animals. So allelopathy is an effect on plants and toxicity is an effect on animals. And yes, some chemicals grown by plants for the purpose of inhibiting other plants can be toxic, at least to some extent, to animals. (Not everything that is toxic is deadly. Sometimes the inconvenience is greater than other times.) One such substance, juglone, is found in all members of the juglans species of trees. The juglans species includes quite a number of nut bearing trees including pecans, hickories, butternuts and walnuts. Each of these species of trees carries juglone in varying amounts.
Pecans, hickories and black walnuts are native to this area. Scientists suspect the nuts, the leaves and the roots of these trees carry juglone in varying degrees. The most common animal reported to be affected is the horse in which juglone is suspected to be a cause of laminitis (founder). We could find no research linking local horses and laminitis to nut trees in our area but research from other states with varieties of black walnut indicated that horses should not be bedded on fresh material from juglans species trees. Queries to several local experts did not find any aware that this has been a problem in Gonzales County but out of an abundance of caution, it seems prudent to suggest that horses not be bedded on fresh shavings from nut trees. Research indicates that aged material is not a problem, but why take the risk? And should any animal owner suspect that their pet or working animal is suffering from any toxicity, they would be well advised to seek veterinary care promptly.
Are allelopathy and toxicity, then, such that we need to completely avoid certain plants? Well, common sense would tell you that we should not be planting hemlock in our gardens but for the gardener who hopes to create a pleasing landscape with juglans species trees, I will be posting a list of plants on the Gonzales Master Gardener website that are resistant to juglone allelopathy. It’s a long list. But in general, it seems that allelopathy is one of many influences on plants in our gardens that we as gardeners need to be aware of. Like so many things, the subject is so broad that we must take it on a case by case basis. Research is certainly on-going in this field and if I spot anything exciting, I’ll be sure to let you know!
Toxicity is the degree that a substance can affect humans and animals. So allelopathy is an effect on plants and toxicity is an effect on animals. And yes, some chemicals grown by plants for the purpose of inhibiting other plants can be toxic, at least to some extent, to animals. (Not everything that is toxic is deadly. Sometimes the inconvenience is greater than other times.) One such substance, juglone, is found in all members of the juglans species of trees. The juglans species includes quite a number of nut bearing trees including pecans, hickories, butternuts and walnuts. Each of these species of trees carries juglone in varying amounts.
Pecans, hickories and black walnuts are native to this area. Scientists suspect the nuts, the leaves and the roots of these trees carry juglone in varying degrees. The most common animal reported to be affected is the horse in which juglone is suspected to be a cause of laminitis (founder). We could find no research linking local horses and laminitis to nut trees in our area but research from other states with varieties of black walnut indicated that horses should not be bedded on fresh material from juglans species trees. Queries to several local experts did not find any aware that this has been a problem in Gonzales County but out of an abundance of caution, it seems prudent to suggest that horses not be bedded on fresh shavings from nut trees. Research indicates that aged material is not a problem, but why take the risk? And should any animal owner suspect that their pet or working animal is suffering from any toxicity, they would be well advised to seek veterinary care promptly.
Are allelopathy and toxicity, then, such that we need to completely avoid certain plants? Well, common sense would tell you that we should not be planting hemlock in our gardens but for the gardener who hopes to create a pleasing landscape with juglans species trees, I will be posting a list of plants on the Gonzales Master Gardener website that are resistant to juglone allelopathy. It’s a long list. But in general, it seems that allelopathy is one of many influences on plants in our gardens that we as gardeners need to be aware of. Like so many things, the subject is so broad that we must take it on a case by case basis. Research is certainly on-going in this field and if I spot anything exciting, I’ll be sure to let you know!