Killing weed seeds

ken1November 30, 2011

When you compost in bins or windrows or even open piles, how can you be sure you've killed all unwanted seed? I would think the outer edges of the pile in the wire mesh type bins would stay cool enough for the seed to survive. I understand you are going to turn the pile, but will it stay hot long enough for the heat to be viable to kill all the weed seed?

I'm asking all this as I have a wealth of leaves available to me, but all of them are on burmuda lawns, and I don't want to be planting burmuda grass anywhere on my property, I hate the stuff. So I've avoided gathering the leaves because of this.

I'd sure appreciate some thoughts.

Presently I compost only in drums so I know ALL OF THE MATERIAL HAS HEATED TO KILL WEED SEED.


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If you actually took the temp you may find the outermost areas of the compost in the barrel are not reaching the min. 140 F required to kill most seeds. After composting spread out the compost and solarize it in thin layers.

    Bookmark   November 30, 2011 at 4:59AM
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Ken - you can't. I have hundreds of tomato volunteers all over my yard from too-cold composting.

You will get more Bermuda grass from bird poop then composted leaves. Most of the seedheads on Bermuda are sterile

    Bookmark   December 2, 2011 at 9:41PM
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feijoas(New Zealand)

I don't try, as I cold-ish compost. Really thick mulch is my answer to pretty much everything. With carrots and suchlike which I don't mulch, I just have to keep on top of the weeds

    Bookmark   December 3, 2011 at 1:29AM
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I think the mulch will work just fine.

    Bookmark   December 4, 2011 at 10:27PM
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Thanks for all the input. I can see your thoughts on using this as mulch, but it seems to me that the seeds will still be viable, and grow , when used as mulch.
Why wouldn't they?
Lazygardens, your thoughts sound good to me, I may try it and hope your right.
Thanks all

    Bookmark   December 5, 2011 at 2:04AM
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The link attached might be of some use.

Here is a link that might be useful: killing seeds by composting

    Bookmark   December 5, 2011 at 6:21AM
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Kimmsr, Thanks for the link, that's some valuable information.

    Bookmark   December 6, 2011 at 1:49AM
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tropical_thought(San Francisco)

Weed seeds are tougher then seeds of plants that one wants to reseed. I have found there is no amount of heat you can generate to kill them. The only solution is to keep weed seed out of your pile. Put them in the compost that they haul to the city compost dump, or in the trash if you don't have a compost pick up. Never put them in your pile or bin.

    Bookmark   December 7, 2011 at 11:21AM
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strawchicago(zone 5a)

Thank you Kimmsr for that link. The link stated that cow manure has weed seeds. A few years ago I put bagged cow manure from Menards on my tomato garden and had the worst infestation of weeds (I had very little weeds prior to this). Then my neighbor put some bagged top soil from Menards on her grass, and it sprang at least 5 varieties of interesting weeds.

I got horse manure from a stable in various stages of decomposition: 3 months, 6 months, 1 years. I mulched my roses with that and had ZERO weeds. Unfortunately, I can't use horse manure for veges with the germs and it's too alkaline with the lime that stables use to deodorize their stalls. The horse manure I got is from a giant pile in open space.

Their horses are fed alfalfa meal and oats. I wonder why there's NOT a single weed in the horse manure, but tons in Menards' bagged top soil, and Menards' cow manure? I tested Menards' bagged soils, and they are less alkaline than EarthGro and Moo manure. There's not much weeds in EarthGro's top soil and Moo manure, but those bags are very akaline, more so than my pH 7.7 native soil. I wonder if the high pH from the lime added to bagged soil (to deodorize ) suppress weeds?

    Bookmark   December 10, 2011 at 4:28PM
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strawchicago(zone 5a)

My neighbor told me that the professional lawn care company put lime on her lawn. I told her, "We are next to a limestone quarry, my soil is tested by EarthCo. with a pH of 7.7 - why do they want to make your lawn more alkaline?" Could they be using lime to suppress the weeds on her lawn from sprouting up in the spring?

    Bookmark   December 10, 2011 at 4:35PM
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feijoas(New Zealand)

Strawberryhill, that manure thing's weird: I've always found the exact opposite, which makes sense when I think of the extra weed-killing power of a ruminant's multiple stomachs.
Horse manure on the other hand, talk about weeds!
Running manure through the compost definitely reduces weeds for me, the rest is done by mulching and hand-pulling.

    Bookmark   December 10, 2011 at 5:56PM
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Not all bagged cow manure has achieved thermophilic temperatures to kill the seeds. Bagged top soil is often just scraped up mud run through a soil shredder and mixed with peat and manure. IOW, no action taken to kill seeds.

If the horses were fed alfalfa meal and oats the only viable seeds would be the oats. If the grain was rolled or milled in some way prior to feeding, those seeds would likely not be viable either.


    Bookmark   December 10, 2011 at 7:10PM
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Most all of the bagged animal manures come from Confined Animal Feeding Operations, or the slaughter house feed lots as they were known when Chicago had large stockyards. The manure is collected and run through heated ovens to dry it so it can be bagged. Some operations don't even do that, however, so you pay for water in the manure. Many of those operations let the manure sit around in piles for a short time (not too long since those manure piles will attract flies) and that is the composting it gets.
Little of that animal manure you buy from any garden center is actually composted, as many of us know composting.

    Bookmark   December 11, 2011 at 6:50AM
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