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decomposing mulch question

Posted by treelover z8b SoCtrlTX (My Page) on
Wed, Aug 19, 09 at 17:43

Earlier today when I was stirring up the mulch on my flower beds, trying to figure out where I'm going to sow various flower seeds this fall, I noticed something that looked like smoke was rising from any area I disturbed. I suppose it was a very fine dust of some sort, or maybe spores from some kind of fungus . . . ??

I'm wondering if whatever it is would keep seeds from germinating, or be detrimental to any seedlings trying to grow there. I usually scrape the mulch back to sow seeds. Last spring hardly any of the thousands of seed I sowed grew. Now I'm wondering if this could be the reason.

I've been getting this mulch from the city for years. Don't know exactly what's in it, but what's there now is over a year old. We've had very little rain this year, so it hasn't decomposed much.

Anyone want to guess what's going on . . . or whether it could affect what I plant there.

Follow-Up Postings:

RE: decomposing mulch question

  • Posted by tapla z5b-6a MI (My Page) on
    Wed, Aug 19, 09 at 18:19

It won't inhibit seeds from germinating. It's almost certainly the bacteria that causes one of the more pleasant rain smells, the one we often notice in the woods. Actinomycetes, a type of filamentous bacteria, grows in soil when conditions are damp and warm. When the soil dries out, the bacteria produces spores. Usually it's the force of rainfall hitting leaves & debris that kicks these tiny spores up into the air where the moisture after a rain acts as an aerosol (just like an aerosol air freshener), but your stirring of the mulch has the same effect. The moist air after rain carries the spores and we breathe them in and often notice the 'scent of rain'.

It's an extremely common bacteria, found all over the world, which accounts for the universality of the sweet "after-the-rain" smell associated with it. Since the bacteria thrives in moist soil but releases the spores once the soil dries out, the volume of spores is greater after a dry spell.


RE: decomposing mulch question

I figured it was something like that, but didn't know the processes involved. Thanks, Al, for taking the time to explain it. Glad to hear it's not harmful.

RE: decomposing mulch question

That "smoke" is spores from the fungus that is busily decomposing your mulch.

Not harmful to plants, but wet the mulch so you don't breath too many of them. They aren't going to kill you, but you can get short-term lung irritation until you have coughed out all the danged spores.

RE: decomposing mulch question

I you planted 1000's of seeds last year then maybe it's time to try germinating some other way. At this time of year I have a lot of slugs and trying to germinate most things in areas that have mulch is futile.

I'm germinating a few things indoors now near a window and I also have some florescent lamps. At least until they get big enough to withstand slugs I'll keep them inside.

RE: decomposing mulch question

Yes, from literally 1000s of seeds I got about 20 poppies, 15 larkspur, 2 bachelor buttons and 5 Mex. sunflowers. A pretty poor return. I may try winter sowing this year. The only thing I can count on to grow is coneflowers.

Thanks for the warning, lazygardens.

RE: decomposing mulch question

Oddly, Actinobacteria seem to have antibacterial properties.

I wonder if you could treat the mulch with an organic fertilizer to amend its C:N ratio and get it to decompose to a point where it will allow seeds to germinate. Partially decomposed material will have substances that inhibit seed germination. Blood meal or cottonseed meal are high in Nitrogen and might do the trick.

RE: decomposing mulch question

This particular bed has been fertilized occasionally with alfalfa pellets but not often, as I have a lot of rosemary growing there which doesn't need or want much feeding.

Another bed where the mulch isn't breaking down much, and seed didn't germinate, contains more rosemary plus a whole lot of sickly looking Russian sage which I've read prefers poor soil. I haven't fertilized that area at all, except for top-dressing individual plants--a rose & some daylilies--with compost a couple of times a year. I just had a soil test done for that bed and was told only to add 1/2 lb N per 1000sf.

I've been blaming all these various problems on the droughts we've had the past couple of years. But maybe I just need to feed my plants more. . . or more often.

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