EasyBloom Forum

I reviewed the info provided on rhubarb which states that the leaves are poisonous, and part of the reason that deer don't eat them. Question 1: Is it possible to cook the leaves so it makes a natural herbicide? I would like to kill some invasive plants (neighbors!) to prevent them from getting into my garden. Question 2: Also, because of the oxalic acid, how far away should the rhubarb plant be from the rest of my garden? My dad had this plant at least 30 feet away from our previous garden. Can rhubarb affect other nearby plants, and stunt their growth or kill them? Question 3: I've also heard that chestnut trees are not good to grow near also. Is that because it also has oxalic acid?

Hey Laurie...Rhubarb has more than just oxalic acid when it comes to toxins, but I am unaware of any that are truly toxic to plants. These toxins (oxalic acid being the most prominent one) are present in the leaves to prevent animal herbivory, which explains why deer stay away from it. Once again, I would like to point out that the petiole, or the stem-like part of the leaf, is what is harvested from the plant for consumption. The concentration of oxalic acid is significantly lower in that part of the leaf as opposed to the blade of the leaf. Anyhoo, being that oxalic acid is toxic to animals and not really to plants, making an herbicide from rhubarb leaves to prevent weed infestation would not necessarily work.

Question 2: The only reason why I can think that you would want to have rhubarb separate from the rest of your garden is that it is a perennial and produces leaves year after year. If the rest of your garden is annuals and you have to dig up the soil each year, you won't disturb your perennial rhubarb crop if it is separated from your annual crop. It is common practice to take the blades of the leaf and compost them to use as fertilizer too. If rhubarb had any compounds that were toxic to plants or prevented plant seeds from germinating, you definitely would not want to compost the leaves to have those toxins in something that you would later spread onto your garden.

Question 3: It is definitely true that chestnuts have compounds in their tissues that can prevent certain seeds from germinating and making new plants. This property is called allelopathy. The most famous of plants that can do this is walnut. They have a compound called juglone that prevents certain seeds from germinating. As for chestnut, I could not tell you the exact compound's name, but it is not oxalic acid that is causing this allelopathy. You may want to avoid using chestnut leaves in your compost.

I hope this is helpful. Let me know if you have any more questions. Cheers...Dr. Robby