Be careful of your source of garden manure: Lingering herbicide could have unintended consequences.
I say it often: It’s all right to make mistakes as long as you learn from them — especially in the garden. Well, I made a doozy recently and have I ever learned from it.
As a full-time gardening communicator, I am aware of the potential hazards of using manure to amend garden soil. In recent years, it has become very apparent that some herbicides used to control weeds in farm fields persist for a very, very long time. Even worse, they don’t readily break down, even through composting. These herbicides that are applied on fields transfer with the hay that you and I buy to feed our animals, which becomes manure that we gardeners love to put into our gardens — and right into my garden!
So if I knew better, why did I do it?
Chalk it up to a dose of cabin fever, combined with my haste to fill my new garden beds — along with a very unscientific assumption that it couldn’t possibly happen to me. My rational for proceeding before proper testing was also flawed. Conscious of the potential risk, I had been observing various weeds and other plants springing to life from this massive, aged manure pile for weeks. I steered my conclusion toward the outcome I really wanted: If weeds are springing straight up from the composted manure, then surely it must be fine in my garden.
You see, not all plants are impacted by these herbicides in the same way. Some are completely unaffected, others only slightly so, while others are severely affected. It just so happened that the ones I observed happily growing were not plants at risk to an active ingredient called picloram. In hindsight, I realize that the plants I didn’t see were the ones the herbicide zapped before they even had a chance to sprout.
Giving myself the green light to proceed with amending the soil with this free and abundant compost, I mixed it in well to each of my garden beds. Then I planted every one with various seedlings, including 20 varieties of tomatoes. And then I waited — and waited.
Something wasn’t right. Why was it taking so long for my new plants to start growing? And when they did, why were their leaves so twisted and other plants so stunted? After a month of hoping for a miraculous recovery, I just confirmed what I strongly suspected early on. The farmer who grows the hay that we buy for our horses made his periodic delivery the other morning, and I didn’t waste a moment in asking: “What type of herbicides to you put on your fields?” He mentioned something that I didn’t want to hear — mainly, the name of an herbicide that contains a persistent substance called picloram, among other ingredients. It’s all I needed to know.
The chemicals to watch out for are aminopyralid, clopyralid and picloram because they can remain active in hay, grass clippings, manure and compost for several years. There’s not much you can do after the fact except wait it out.
What will I do now? I’ll grow out the plants that are already there because I want to see how they ultimately respond. After that, I’ll turn over the soil in the beds to expose it to more sunlight, air and moisture, and promote the soil microbe activity by making each bed a working compost bin. This will build up the heat deep in the soil and break down the herbicides more quickly. Compost has a wonderful way of neutralizing lots of harmful soil ingredients.
What should you do? Never use manure in garden beds if you are not sure of the chemicals used in the field that fed the animals. For now, it’s the only way you can be sure you are not transferring harmful, active herbicides to your garden. And farmers have a responsibility in this as well. They should inform customers when using herbicides that can be potentially devastating to home gardeners when transferred by a product they provide.
My garden will eventually recover. But I can say with certainty that this is one mistake I know I’ll never make again. Hopefully, I’m keeping some of you from making it in the first place.