weed seeds in compost

old_dirt(5b)May 15, 2009

I've got about a zillion weed seeds in my almost finished compost. Mostly garlic mustard I believe. Any ideas on how to get rid of them? It's a large pile, about 4' x 6' x 3 1/2' high. What about cooking it under black plastic.

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Cooking under plastic seems counterproductive to me. You'd cook all the beneficial bacteria along with the seeds. If it was hot composted, the seeds shouldn't be viable, anyway. I've also seen reports that even cold composting, if done long enough, can kill the seeds.

If you decide to cook the compost under plastic, clear plastic might work better than black. Pick a time when it's hot and sunny and expected to stay that way for a couple of days. Put the compost out in a sunny spot, get it damp and cover it in clear plastic. The plastic will act almost like a magnifying glass and cook everything under it. Be aware that this will also kill any and all plants under it.

    Bookmark   May 15, 2009 at 8:36PM
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You have discovered why I no longer compost weeds even close to producing seed. It just isn't worth the chance. Some weed seeds are more heat tolerant than others, and few home compost piles get hot enough, long enough, throughout the pile to kill them all. You don't have to miss many weeds to end up with a big problem. Mine now go into barrels to ferment for a year or so in water. I'm still not ready to put them in my compost just yet... At least not before a germination test.

    Bookmark   May 15, 2009 at 9:35PM
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dchall_san_antonio(8 San Antonio)

Let them sprout in the compost, then turn the compost.

    Bookmark   May 16, 2009 at 12:09AM
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There is some research that shows "weed" seeds in compost can germinate but then die, due to lack of access to sunlight, so simply maintaining the compost pile is all that is needed to solve the problem of "weed" seeds in compost. As Dave has suggested turning the compost and alloowing it to sit for a time will cause and that do germinate to die.

    Bookmark   May 16, 2009 at 7:08AM
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Hi, new here! I just yesterday cleaned out a lot of winter die-back of english ivy which had grown up my fence, (esp. harsh winter this yr) and beneath found a treasure cache of moldy leaves and resultant rich loamy soil scrapings. Have a box full, and hate to throw out, but am terrified that bindweed seeds could be present, (as well as dandelion seeds) as my next door neighbor's adjacent yard is utterly untended, and this cache could well contain some. What should I do please? I have limited space for composting, and have not been good at it in the past. :) But hate to part with this rich mix by handing it over to the city to compost on trash day! Thanks for any advice. Yes, bindweed has been such a terror here, I finally broke 21 yrs of my "organics only" policy, and last yr was diligent at my new "hunt & spray" program, which was hugely successful, must admit. I still have new sprouts, but within dozens, not thousands. They will be sprayed, next calm hot day. (Bindweed seeds survive up to 50 yrs I have read) Any hiding will outlast me at this point, so I shopuld have sprayed them at outset. (by way, my method was to untwine each strand, coil in a little heap, and spray entirety, at times placing cardboard beneath to shield other plants. Apoligies if straying from forum. I am wondering if it is safe to use this box of moldy leafy matter. :) cheers & thanks

    Bookmark   May 16, 2009 at 9:43AM
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flora_uk(SW UK 8/9)

"Terrified" seems a slight over reaction. I compost weeds in flower and seed all the time in my cold heaps. Any which germinate during the process get turned in like dchall says. If they germinate after the compost has gone on the garden they get pulled (easy in well composted soil) and added to the next compost heap. Really not an issue to get het up about. After a few years there are very few weeds to deal with anyway as the seed bank in the soil gets depleted. The only weeds which I don't compost are bindweed roots. And I will put these in if they are thoroughly dessicated. I do this by draping them over any convenient branches or wire for a few weeks.

    Bookmark   May 16, 2009 at 1:23PM
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i remember reading a post where trudi and kimmsr attacked a newbie for saying they didnt compost any weeds that had seeds because it just spread more weeds. kims big claim was the seeds have all the nutrients. but they also start more weeds too

    Bookmark   May 16, 2009 at 2:16PM
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Thank you darkcloud! Bindweed is a noxious problem here, and that's an understatement. I've ripped out the entire surrounds of garden and perennials trying to get each length of root, without any lasting benefits, so merely pulling weeds is not the solution to bindweed. Plus it is too disturbing to the perennials, so I don't wish to chance ANY seeds entering from compost. Just wish I knew how to effectively 100% burn down the seeds thru composting. Bindweed is so destructively invasive in the states now, it actually has a death warrant on it in some counties and states. (by law must be destroyed!) cheers, and thanks darkcloud :)

    Bookmark   May 17, 2009 at 6:55AM
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gumby_ct(CT it says Z5)

I remember that post darkcloud.

I was able to effectively stifle bindweed in my yard and have done it with other weeds since. I did it by hand pulling every seedling I saw starting in the spring, as soon as it sprouted. Early on it was quite consuming but this year I don't think I pulled more than 4 seedlings. This is the 4th yr.- each yr I had fewer and fewer. The key for me was learning to recognize them early.

But I too had the philosophy that any weeds with seeds got sent off to the dump. Now that I have learned to hot compost, I am not as regimented with that but have learned no matter how hot you get the pile, the outer rim will never be hot enuff to kill weed seeds. Leaving billions behind. Did you know weed seeds can live up to 40 yrs waiting for the right condition? Most are not visible to the naked eye.

Early on I experimented by steaming my compost (using a gas grill and cast iron pans) to kill the weed seeds. While this is quite effective, it also adds to the time & expense. Then as others have mentioned, I thought I was killing off the good guys with the heat too.

I am not sure how the manufacturers sterilize their products? Anyone know?

    Bookmark   May 17, 2009 at 9:08AM
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flora_uk(SW UK 8/9)

darkcloud - I am assuming you are implying that I was 'attacking' the o.p. I think we have another of our transaltlantic linguistic misunderstandings here. Maybe a little everyday Brit tongue in cheek went awry. I've been posting here for a long time but still get caught out by the literality and sensitivity. I just think that it would be good if some of the composters on here lightened up a bit and didn't take it all so seriously. Poor old wildbarret says s/he has not been 'good' at composting in the past. That is highly unlikely. I'm sure wildbarret's efforts were probably absolutely fine but s/he feels a failure because of the over complication and mystification of the process by the compost police. It is the perfectionists who make people say they are 'terrified'. To me 'terrified' is what you would feel in a plane crash. 'Slightly concerned' is more descriptive of one's thoughts about a few weed seeds.

Believe me, I do know about bindweed. When I took over my neglected allotment I hand forked it thoroughly foot by foot and removed every piece I could find. As gumby says, hand weeding for a few years WILL eventually work. But 'pulling' is not enough for things like bindweed. Even the tiniest piece will grow. You need to fork and fork thoroughly.

I have gardened for well over 40 years now and can only tell it how it is for me. I put all annual weeds in the compost heap, whether seeding or not. I cold compost by default rather than intention and have five heaps on the go at any one time. I am a little more careful with perennial weeds but still add them and just keep an eye open for them when I use the compost. The only exception to this regime is, as I said, fresh bindweed roots. I would not put Japanese knotweed in either, but luckily I don't have it in my garden.

annpat - please come and pour a little oil for me - I sometimes think you are the only person out there who speaks my language. (select appropriate emoticon)

    Bookmark   May 18, 2009 at 9:56AM
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no sorry. i was talking about kimms and trudi badgering a newbie who didnt want to add weed seeds to compost pile. not sure why you would feel so guilty, soory

    Bookmark   May 19, 2009 at 7:37AM
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