The Worst Amendment for Lawns: Sawdust. (Or, What I Learned Today #1)

Refusing to be scared off by unfortunate acronyms, I’m starting a whole series of posts to be titled What I Learned Today. This is the first.

As you can see from the #1 in the title.

Though I could have put that there just to confuse you.

But I didn’t.

I’m beginning to sound like Esther. Or Winnie the Pooh. Yippi!

Down to business:

A couple of years ago I read that sawdust was the last thing you wanted to sprinkle on your lawn (unless you liked that sickly yellow color), but I’d completely forgotten why. This did not keep me up at night until recently, when I was working on the soil amendments part of my endless organic lawn care article (I’m up to page 112, and counting), and wanted to say something intelligent about sawdust as an amendment.*

Back to business:

It didn’t take much scratching around the Internet to learn that the reason you shouldn’t scatter sawdust on your lawn or mix it into your soil as organic matter is that it requires nitrogen to break down, and it’ll make use of whatever it can lay its sawdusty little paws on. And the nitrogen it uses is therefore not available to your plants. Once the decomposition is complete, the nitrogen is released and once again available, but until then, it’s tied up, like a businessman at the twelfth hole: “Yeah, Joe? Look, I can’t make that meeting, I’m tied up.” It is unavailable, like a member of upper management over a two-Chardonnay lunch: “I’m sorry, Mr. Malcolm, but the Director is unavailable at the moment. Can I take a message?”

The problem with this explanation—aside from those awful, irrelevant, downright prejudiced similes—is that it would seem to apply to everything. Why would sawdust require nitrogen to decompose, but not leaves or grass clippings?  Yet THEY tell us (and now I’m one of THEM, I’m telling others, via this article, if I ever finish it (which is unlikely, as droves of men in business-suits are swarming the house, looking eager to see how quickly I will compost)) to leave clippings on the grass to decompose, providing nice organic matter where they lie.

I decided that sawdust must simply require more nitrogen to decompose than did leaves of grass or leaves themselves.

Today, reading the book my SO got me for my birthday, James A. Nardi’s Life in the Soil: A Guide for Naturalists and Gardeners, I stumbled on the answer in the form of a little list of various soil elements and their nitrogen content. (Business-men not included.) It seems that I was wrong, but still sort of right. Sawdust doesn’t require more nitrogen to decompose, but it contains less, so it (or the micro-organisms trying to eat it) takes more from its environment, which, if you’ve sprinkled it on your lawn, is the soil from which the grass is also trying to get nitrogen.

So the end result is that YOU SHOULDN’T INSULT UPPER MANAGEMENT—no, that’s not it.

Take two:
YOU SHOULDN’T SPRINKLE SAWDUST ON YOUR GRASS. Or on or around other plants, though it's especially an issue for lawns since they need so much nitrogen, and if you put it in your compost, add LOTS of green matter or blood meal so it can decompose properly.

There. Done. Now, about those fellows swarming the house–I need to get to the roof and call for a helium balloon. Anybody got a balloon to spare? Preferably with a basket….  (Did you hear the one about the guy whose balloon took off without him, leaving him and his basket behind? True story.)

*This may—or may not—be the place to point out that Andrew Marvell might say, “But at my back I always hear/ Time’s winged chariot drawing near,” but I would have to say, “But at my back I always hear/ my kids' ironic voices dear.” Which should clarify why he is a much more famous poet than I.

As soon as I write a line like the one about saying something intelligent, I imagine son the second laying a kind hand on my shoulder as he shakes his head; son the first and I are already starting to giggle—we can see where this is going—as second son says sadly (as sadly as he can manage, which isn’t very), “Well, Mom, you may as well give up now.”

5 Responses to The Worst Amendment for Lawns: Sawdust. (Or, What I Learned Today #1)

  1. I laughed so much as well as learning Kate. I was shouting – ‘it’s the nitrogen of course’, but never knew it’s because there’s less of it to help with the breakdown process.
    Neither did I, and it’s been bugging me, so thank god (or Nardi (author of the book), or Steve (for giving it to me), or all three) for coming through in a pinch.
    I still don’t know why the microbes can only take nitrogen from the soil, and not from the air in the soil. Oh well.
    –Kate

  2. Sawdust was never funny to me before. Now I will not be able to look it in the face without snickering.
    So I’ve caused someone to snicker at sawdust. My life has not been wasted after all.
    Thanks for reading, and for commenting.
    –Kate

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  4. I have to say, I don’t think this is correct. Sprinkling organic matter on the ground is called mulching, mulching with anything is better in almost any case than not mulching. The air is 80% nitrogen, and therefore, if mulches are applied to the surface and not incorporated INTO the soil, the micro organisms that require nitrogen to break down the wood can get it from the air readily.

    Grass roots for instance, can be 3-6 inches deep into the soil. Adding some sawdust sprinkled to your lawn is going to have no impact to anything under the first millimeter of soil that it actually touches. The grass will be just fine, and the sawdust may actually rob enough nitrogen right at the soil surface where a weed seed may have landed to inhibit it’s growth when it germinates.

    The one issue I could see with sawdust is that it is so fine, that it could mat if applied too thickly, this could cause water to runoff rather than penetrate and cause areas of excess dryness. I think it could also inhibit airflow and therefore also inhibit gas exchange.

    So while I don’t think it is the ideal solution to add organic material to a lawn or garden, I would certainly consider using it in small amounts or especially adding it to other organic material like grass clippings or shredded leaves for a garden mulch. I have even read about people spreading hardwood pellets (compressed sawdust) to their lawns to add organic materials with good results.

  5. Loved this article along with slagathore’s respond.

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