Contaminated Clippings: Death From the Lawn!

Q. Jim in Gilbertsville PA writes: "I used soil mulched from grass clippings from my lawn which is treated with common weed & feed. Now I have learned the difficulties of growing vegetables in this soil--the hard way. Is there any way I can dilute the wilting effects this contaminated soil has caused on my tomato plants? And if I can harvest any tomatoes from these plants, is the fruit safe to eat?? And am I the only person this has happened to?"

A. Thanks Jim. Now that we're in the middle of lawn mowing season, your loss may save many other gardens from a similar fate. The 'weed' part of the notorious "weed and feed" is, of course, a chemical herbicide; specifically one designed to kill any plant other than turf grass. If you still have the bag, it should contain a specific warning not to compost the clippings.

The reason for this is that some chemical herbicides are so persistent they survive the composting process and remain active enough to kill non-grass plants. This was first reported decades ago by a University that made their own compost and used it to feed the bedding plants they were raising for their annual Spring plant sale. All the plants died, which confused the composters as they had had the finished compost tested and there was no evidence of herbicide residue.

Then one of them said: "we tested for residues at the parts per million level. Let's test again at parts per billion". And there they found the guilty party. It had killed plants at a level so low its almost unimaginable. But dead plants do tell the tale.

Now, it's a little hard to figure out whether you used your clippings to make compost or if you used them to mulch your dead tomatoes. Either way is wrong, even if the lawn is not treated with chemical herbicides, because clippings belong ON the lawn. Those clippings are ten percent nitrogen, and ten percent nitrogen is THE perfect lawn food. Lawns don't need potassium or phosphorus; and fertilizers that contain phosphorus are banned in many areas, including the states of Virginia and Maryland, where the phosphorus ban is designed to help clean up the priceless Chesapeake Bay. It's also against the law in these states to use a fertilizer that is higher than ten percent nitrogen; again, to try and protect the Bay.

As I travel around the country, I see more and more municipal composting sites that have been burned and now have big warning signs posted: No grass clippings!

But I know I'm fighting an uphill battle. Many (perhaps most) books on composting include grass clippings as an acceptable raw ingredient, along with shredded junk mail which is just stupid. Same with composting classes held by well-meaning Extension Agents and/or their Master Gardener volunteers, who are often just passing along old information without thinking much about it.

Example: A few years back I accompanied a friend to a composting class at a large and prestigious University in Philadelphia that was not Temple or Drexel (nor St Joe's or Villanova which are outside the city proper). My friend made me promise to behave and I lied that I would. When the woman teaching the class said to include grass clippings, "I raised my hand and asked, "don't you mean clippings from a lawn that hasn't been treated with herbicides?" She seemed puzzled, and then I explained the dangers of clippings from a treated lawn while my friend repeatedly elbowed me in the ribs.

Then we got to leaves and I said "of course you mean shredded leaves, as whole leaves mat down and stop the composting process". Then she moved on to shredded junk mail and cardboard and I was given a really nifty composting bin and asked to leave the workshop before she got to kitchen scraps.

Back to Jim. No, you are not alone. This probably happens to thousands of gardeners every season, but they email me complaining of a 'blight' or a 'fungus' and don't connect their tomato death to grass clippings which YOU, Jim, did. So, to quote storyteller Garrison Keillor, "you knew it was wrong and now you know it".

Direct answers: Years ago we told people whose land had been sprayed with herbicides to flush the area repeatedly with long drenches of water, but I fear that won't affect this new generation of persistent and systemic products. I would not try to save those plants and I would not eat their fruits. These pesticides are systemic, which means they get into every cell of a plant.

If you mulched your garden with grass clippings, get rid of them. Wearing gloves. If you made contaminated compost, spread it on the lawn, where it won't harm anything.

In the future, if you feel you MUST use weed and feed, try corn gluten meal. It prevents germination of weed seeds and feeds the turf without any chemical fertilizers or herbicides. In addition, limit the amount of weeds naturally by using good cultural practices: Never cut grass shorter than three inches. Always cut with a sharp blade. Always leave the clippings behind. And when you water, water deeply and infrequently.

And, as they used to say on the old Mission Impossible TV show, "Good luck, Jim."