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Fall is THE Time to Make Compost Magic

Q. I just watched the video of your TEDx talk on composting fall leaves and found it to be tremendously enlightening. Can you do the same thing with lawn clippings and/or hay?

    ---Cenzo in Finland, PA

A. 'Finland' in Pennsylvania?! Sounds fishy to me, but Map Quest says it's there; just a few miles North of Philly, near Quakertown. Small world, eh?

Anyway, the answer to our 'Finlandier's' question is no, especially for grass clippings—for two reasons:

  1. If the lawn was treated with chemicals, the resulting compost could be toxic to any plants other than grass, as some of the more "modern" herbicides can survive even a complete and thorough composting process—and that's the kind of "Killer Compost" you don't want to make.
  2. Grass clippings are 10% nitrogen, which makes them perfect lawn fertilizer. Using a mulching mower to return those pulverized clippings to the turf provides half the food your lawn needs in a given year. And it helps break down thatch by increasing the number of beneficial microbes at the soil line. Conversely, collecting your clippings starves the lawn and reduces life at the soil line.
  3. As I explain in that TEDx talk, compost piles should be composed of at least 80% well shredded, nutrient-rich, dry carbon materials—specifically fall leaves. Adding too many wet green Nitrogen-rich grass clippings can really throw the balance off. And trying to compost grass clippings alone just makes a big stinky mess.

Yes, I know that that's three reasons. Sue me; I left a tip.

Now, hay is problematic for the same herbicide reason. Virtually any hay or straw you're going to be offered for sale was grown "conventionally", meaning it was fed cheap chemical fertilizers and grown in fields that were potentially sprayed with the same kinds of chemical herbicides that make grass clippings unsafe for composting.

By the way (Or 'BTW' to those of you much hipper than I), this 'hay issue' has also led to the problem of contaminated manure— when horses and cattle have been fed hay that was grown in fields treated with these persistent herbicides.

It's a real shame. Adding a little bit of horse manure to a lot of well-shredded fall leaves used to be a great way to add Nitrogen to the mix and make better compost faster. In fact, many old-school organic growers felt that compost with some animal manure in the original mix had the absolute best disease-fighting potential. But these new highly persistent herbicides have changed everything. If the animals were fed suspect hay or grazed on a treated pasture, their manure could make your seemingly wonderful home-made compost deadly to garden plants. It's just not worth the risk.

Luckily, people can instead use spent coffee grounds to provide the Nitrogen that makes better quality compost. Which leads us to another compost question…

Q. I've been accumulating leaves for years under a giant Norway Spruce in my organically-cared for yard. I sprinkle coffee grounds on them from time to time, but have never tried shredding them, as you recommend. The top layers stay dry and brown, but way underneath, there is a layer of dark, wormy soil. Is there a problem with continuing this method? If I need to shred them, what are the best ways to do so? Would running a mower over the pile work?

    --- Pattey in Wayne, PA

First, this is a perfect example of why it's so beneficial to just collect all the fall leaves you can, no matter how you do it. Even un-shredded, they eventually become a fine fertilizer, mulch and soil improver. But the process takes years longer without shredding. And this specific pile could constitute a long-term danger to that tree if the leaves are actually touching the bark or piled so deep that they're preventing water and air from getting to the roots. So the first thing I'd suggest is an old-fashioned 'turning'; use a pitchfork to move the pile further away from the tree. This will also allow our somewhat-lazy listener to harvest that nice finished compost at the bottom.

Then to handle this season's leaf fall, I strongly suggest you start shredding, and my top choice for the chore is an electric blower vac. They're inexpensive, shred the leaves as they suck them up and you don't have to do any bending or raking.

Or, when the landscape in question is organic, you can instead rake, push or blow the leaves on top of the lawn and, yes, run them over with a bagging mower. That would shred and mix them up with a nice little amount of grass clippings; creating a perfect combination of the dry brown material that actually becomes the finished compost and a little wet green Nitrogen to feed the microbes that fuel the composting process.

To repeat, in this case, grass clippings are okay because:

  1. they're from an untreated lawn,
  2. will be really well-mixed with lots of shredded leaves,
  3. and will only make up a small percentage of the pile.

But if your lawn is treated (boo; hiss!) or it's too much work to drag your leaves all over the place, just shred all the wonderful fall leaves you can and mix some spent coffee grounds in as you pile them up or pour them into your composter. Either way, you'll have great compost for next season's garden.

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