Kitchen Garden Forum

Hi all,
A gardener on our site says that he always composts the weeds as he only uses that particular compostheap "every other year",and that this kills any weed seed in his heap.

Any thoughts please?

Regards,
Mark.

Hi Mark,
Sadly what you have been told is not true. Seeds can last many many years and they bypass the degredation process in the composting and spring into to life when you turn them up. If the compost is well dug in they may not grow that year but the next time you dig that plot you will bring them to the surface and they are off again!

Does it work for him? Maybe he manages to get seed-killing temperatures, or turns his compost heap so the seeds start to sprout then get buried and die?

Weed seed in my compost isn't a concern, as I use it as mulch (no-dig). If any annual seeds start to sprout, another layer of mulch on top smothers and kills them

The same applies to roots of perennial weeds. We traced a dock though 3 foot of compost, still alive.
One can however discretely save weedy material while it is in the state of not having had a chance to set seed, but be very wary of such as dandelion heads which can mature off the plant.
How about my system, two bins, one for clean, one for dirty, which includes infected material. One day the dirty compost will be spread out and anything that comes up will be snuffed out.
Allan

We put 'clean' weeds on the compost heap, but save seedy weeds and the perennials in plasztic sacks which are periodically taken to the dump for recycling as green waste. They can achieve high enough temperatures to kill off any weed seeds or roots...

You can kill perennial weed roots and weed seeds by 'composting' them in water. Six months' immersion will kill anything non-aquatic, and you can then tip out the residue on your compost heap. You can also use the liquid as a feed (diluted if it's dark).

Thats a great idea Jenny; does it smell really bad?

Hi Jenny,
It certainly is a good method as most perennials have a very good array of vital nutrients.
I did an experiment a few years back with Ground Elder using this method and the results were amazing.
I believe Angi uses this method if my memory serves me well as I am sure she mentioned it the last time this question came up. I found that once the weeds had started to decay (it takes only about 3 weeks)
the liquid can be drawn off to give a weekly feed and the water topped up again and the surprising thing is that you can keep topping up with more weeds and more water and as fast as you use the liquid the weeds seem to deteriorate to keep pace and the drum never gets full.
I suspect that very few Compost Heaps ever reach a high enough temperature to destroy the seeds. I have had FYM too hot to touch and the B----y Nettles still seem to germinate.
Sincerely, Johnboy.

Yes, Johnboy, you're right. I do use this method, and very effective it is too. Although I have a fairly weedy (but well managed) plot, I never need to use more than one water butt, topping up with water as the season progresses. I only empty the gunk out once a year, in the winter, when the stink is less of a problem!

Chantal wrote:Thats a great idea Jenny; does it smell really bad?

Yes, it does stink a bit!
I'd like to take credit for the idea but I got it off Bob Flowerdew, who (I think) got it from the Romans.

I am the gardener who composts everything, weed seeds or chunks of doc make no difference on my site, as about sixty percent of plots have weeds that are blowing seed all over at this time of the year, what I tend to do, is dig several two foot trenches and bury the material. if it turns to a weed when I dig it over the next year I either hoe it or pull it, weeding is something I am not sure we can avoid on sites like mine, however, for me it is a great source of free organic matter, the choice is down to each plot holder. For me the only manure I can get has to be bought and I don't put any chemical fertilisers in (as most of you folk know by now) so if you have a site free of windblown weed seed, then composting everything might not be good, however, it works for me!!

And yes a really big well turned heap of mixed material including some straw twigs and soil really gets hot, whether or not it is hot enough to kill the seeds or tap roots........I am not bothered!!!

Compo

In ancient times they used to leave the ground fallow as part of a rotation to let the weeds and grass improve the soil so there must be a case for doing something similar nowadays. Isn't this really the same as green manuring.
Allan

Hi Allan,
Probably nine out of ten fields left fallow were under-sown with clover and certain other varieties of plants with the previous crop and this is why I am always reminding people that although the Organic Organizations lay claim to inventing Green Manuring it was in fact part and parcel of normal agricultural practice long long before they ever came along. So that although the Organic movement may not have invented green manuring they have certainly introduced it to the normal gardener and in doing so have increased the varietal scope with many more now being available.

The point I am getting round to is that Compo may have something in using the almost inevitable buildup of weeds and grass in the winter to do your green manuring for you. We seem to be hooked on a regime where the weeds are killed off and the soil lays bare all winter with losses of essentials and then bring in material from elsewhere to replace it, with a good chance that the farmer supplying it has used chemicals to grow it having sold off his valuable manure to the gardener. Time was when with mixed farming this didn't happen.
Organic it may be but not good for the environment.
Allan

Sorry, Allan, you're not making any sense to me - are you saying that killing all the weeds off and leaving the fields bare is an Organic practice? Also using chemicals and selling your manure to the gardener?
Because I would have to disagree with you there.