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Trash-picking? Or Treasure-Taking? Making Compost with Other People's Curbside Leaves


Q. I've been 'stealing' what you call SPBs from my neighbors (much to their confusion) to add the precious leaves they contain to my compost pile as per your frequent recommendation; and I have two questions: First, the bags say that they're compostable, and I've thought about running them over with my lawnmower along with the leaves they contain; but would they add any actual nutritive content to the compost? Second, a lot of the bags have small amounts of grass clippings mixed in from the leaves being picked up by a mower going over a lawn. I know that the combination of clean (chemical-free) grass clippings and shredded leaves can make good compost fast. But if the lawns were treated with chemicals, could enough contaminants still be present to hurt my plants? Thanks!

---Joel in Huntingdon Valley, PA

A. Thank you for a great question, Joel; and timely too, as it will soon be last call for this year's leaves!

Now, "SPB" is the somewhat ungracious name I coined years ago for those over sized special, 'yard waste' bags that people must use when they put things like leaves, prunings and grass clippings out at the curb for trash pickup (so that the priceless organic matter they contain can be diverted to a composting facility). However, some people are understandably upset by the first word of this designation, so let's just call them 'less than Smart' People Bags. Ahem.

At any rate, at this autumnal time of year, the material inside those bags tends to be mostly leaves, which are THE priceless resource for organic gardeners. Shred them up and pour or rake them into a pile or a bin, and those leaves will become fabulous rich, black compost—the backbone of any organic landscape. And shredded leaves alone make a superb natural mulch—preventing weeds, retaining soil moisture and encouraging earthworms to improve the soil underneath.

That's why most organic gardeners are furiously shredding all the leaves they can gather at this time of year; you never get to August wishing you had made less compost or saved fewer leaves. And, when all of our own leaves have been shredded, mulched, piled or binned, many of us look with longing on those long rows of brown treasure chests sitting out at the curb. Discarded! Like trash!

So yes, seize the SPBs and seize the day! We are not trash pickers! No, we are treasure takers!

Now, I have developed several ways of utilizing the giant containers that hold this treasure. Your instincts are correct that processed brown paper bags contain little to no nutrition, but the bags themselves are good and sturdy, so I use some of them for storage of shredded leaves (for mulching or future compost making). Any type of shredding—whether with a blower vac, chipper/shredder or lawnmower—will reduce the volume of a pile of whole leaves by at least a factor of ten; so I can refill one bag with what had been ten bags of whole leaves. I'll store the bags in a cool dark place where composting will be kept to a minimum and then use that wonderful material as mulch in parts of my vegetable garden. (Shredded leaf mulch attracts earthworms, who then feed the mulched plants for free with their fabulous castings.)

Most of the rest of the bags will be sliced up and used as weed barrier in the lanes between my raised beds. But if a batch of bags is in perfect shape and filled with nothing but leaves (no soda cans, food wrappers or other trash), I'll sometimes carefully refold and return them to the house they was trash—eh, treasure—picked from. (With a thank-you note, of course!)

Bags of mixed waste that include grass clippings are much more problematic. As we've been warning listeners for the past year or so, some of the newer "improved" lawn herbicides are so persistent and so deadly to non-grass plants that compost made from the clippings can kill entire gardens. So you have to treat such bags with caution.

Sometimes, I'll get a bag that has a clearly defined combination—like grass clippings in the bottom and leaves on top. In those cases, I'll put all the clippings back into the bag for curbside disposal and save the leaves.

True mixtures of shredded leaves and grass clippings that were collected from the leaf drop on a lawn are more problematic. On one hand, you don't want to risk contaminating your compost. On the other, SPBs that contain pre-shredded leaves are more tempting than Belgian chocolate! And mixtures of shredded leaves and grass clippings really do create hot, high-quality compost. So I keep these potentially wonderful and/or deadly packages, but in strict isolation.

Designate a bin, tomato cage or composter for such material and label it clearly. Let it compost over the winter. Then next season, shovel some of the finished material out from the bottom and test it for herbicide residues before using it for real. Plant some pea seeds (which are extremely herbicide-sensitive) in a container of the compost, water it well, and then place the container out in a warm room indoors. If the seeds sprout and the young plants are healthy, the compost should be safe to use.

And if we're talking about YOUR clippings being dicey, get your lawn off drugs! Switch to all-natural lawn fertilizers, and bag up that great combination of clippings and shredded leaves without fear!

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