permaculture

[yarrow@sfo.com]

I haven't heard of devices that burn out weed seeds, but I'm skeptical.

I have heard of solarizing for "burning" out some weed seeds, and 
yes, it does also bake out beneficials in the soil. But it affects 
only the top layer (exactly how deep depends on how hot the summer 
sun, duration the plastic stays on the soil, moisture level, type of 
soil, etc., as well as prep work before laying down plastic sheets -- 
till, water, till again, water again, to force germination of as many 
weeds as possible), so if you then disturb (till) the soil, you may 
bring up more weed seeds.

Flame weeders and burning are totally different techniques, though.

The purpose of flame weeding is to heat up weed tissue enough to cut 
off circulation, so that the plant eventually withers and dies. In 
other words, the plant is heated just enough to damage it, not scorch 
it. The best time to use it is when the weeds are lush and green -- 
you don't want to use it on partly dried (flammable!) weeds. I've 
heard about steam weeders that do the same thing.

Myself, I'd rather pile on the cardboard/newspapers and mulch. So 
far, in the relatively small areas where I've worked (less than 1K 
sf), this has been sufficient to get rid of bermuda grass, bindweed, 
and mallow within a season.



At 11:44 AM -0800 12/18/06, Rob Kelly wrote:
> Just last night I was talking with a friend who
> was curious about  "fire weeders" -- propane
> powered contraptions that you use to burn out any
> weed seed.  (You wheel along like a vacuum and
> everything under the hood gets torched.)
>
> I wondered whether such heat also killed
> beneficials in the soil, or whether those deeper
> in the soil quickly repopulated the top layer
> that was burned.
>
> Now that I think of burning as a tried and true
> technique, I wonder again whether these fire
> weeders, propane consumption aside, are a pretty
> good idea.