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Saturday - May 11, 2013

From: Rusk, TX
Region: Southwest
Topic: Invasive Plants, Pests, Edible Plants, Poisonous Plants, Trees
Title: Affect of poisonous plant roots in soils for vegetables from Rusk TX
Answered by: Barbara Medford

QUESTION:

I have a huge old flowerbed in front of my house that I want to plant veggies in, but I'm afraid to. It has a catalpa tree there, which I sell the worms from, but the entire tree (bark, leaves, flowers, seed pods, and roots), are all poisonous. We just dug up Lantanas and transplanted them elsewhere, but they're also poisonous. Some of the roots are still in the ground. They went too deep for us to get them all. There were also holly berry tree/shrubs there, but we cut them out, too. Being these all have poisonous roots/parts, etc., if I planted edibles in this flowerbed, when watered, would they not absorb the poisons from these plant roots!?! We don't want to poison ourselves. Should I just re-plant flowers instead?

ANSWER:

Mr. Smarty Plants learns more from his clients that he would ever know otherwise. When you referred to selling worms from your catalpa tree, we envisioned digging earthworms out of the moist earth in the shade of the tree. We went to a Floridata site which gave us this interesting piece of information:

"This tree has been widely planted and naturalized outside its native range because it is the host plant for a caterpillar commonly called the catawba worm. These are a popular fishing bait for southern freshwater fish known as bream."

We went to our Native Plant Database and found 2 catalpas native to North America:

Catalpa bignonioides (Southern catalpa) - USDA Plant Profile map showing it native to a few counties in East Texas, although not Cherokee County.

Catalpa speciosa (Northern catalpa) - USDA Plant Profile map showing it native to a few more counties in East Texas, but again not in Cherokee County.

You might want to read this previous Mr. Smarty Plants question about poisonous non-native foxglove around vegetables. Although most vegetetables are out of our range of expertise in that they are either non-native to North America or so extensively hybridized that their origins are impossible to determine, we will try to determine if roots of known poisonous plants can transmit those poisons to other plants. In our search for information on this, we found definitions of two processes that can remove toxic substances from soil through use of plants. These definitions are from Wikipedia:

"Rhizofiltration is a form of phytoremediation that involves filtering water through a mass of roots to remove toxic substances or excess nutrients."

"Phytoremediation consists of mitigating pollutant concentrations in contaminated soils, water, or air, with plants able to contain, degrade, or eliminate metals, pesticides, solvents, explosives, crude oil and its derivatives, and various other contaminants from the media that contain them."

These indicate to Mr. Smarty Plants that plant roots can take toxins out of soil, but not that they can inject poisons into soils. Here is another previous Mr. Smarty Plants question that deals with the effects of possibly poisonous roots.

However, search as we would, and there are lots of research resources on the Internet these days, we could find no indication of any danger of food crops sharing a bed with a plant with poisonous parts. In fact, we found no proof of the poisonous nature of all parts of the catalpa that you mentioned.

As we said, we don't know anything about raising vegetables, as they are out of our line. We do feel that planting vegetables in a heavily shaded area under a messy tree full of caterpillars is pretty unappetizing. Apparently, all the leaves are chewed off the trees every few weeks by the fishing "worms," meaning all kinds of stuff would be constantly dropping on your edibles. Finally, we are pretty sure that the catalpa is defending its turf with far too much shade and a wide network of underground roots for anything else to grow well.

Bottom Line: If you do manage to grow any vegetables in that inhospitable environment, wash them really really well.

From the Image Gallery

Southern catalpa
Catalpa bignonioides

Northern catalpa
Catalpa speciosa