Sterilising home made compost

[rary]

If I sterilised home made compost would I loose or gain any benefit from doing this, I can sterilise with dry heat or steam, so what would be the most benificial way of doing it, and would it be worth while doing it

[mothhawk]

It would kill weed seeds and any pests but you would also destroy all the beneficial bacteria, microbes and fungi that help plants to grow. if it's just for seeds that's OK as they'd soon be potted on into living compost I presume, or if you are going to liquid feed with the nutrients that microbes would provide.

[Nicos]

I’ve never really got my head around the right temperatures for this. I’ve read quite a bit on line and still am confused.
As MH says, you don’t really want to kill good bacteria, but in reality everything is going to be killed off over a certain temperature.
What sticks in my head is that proteins ( ie insects) break down at just over 40C and around 100C most bacteria die.
Also steam burns more than water at the same temperature.

How all that works together with sterilising compost I suppose is what you are intending to kill off.

Interesting thread Rary……I’m keen to understand this too!

[Nicos]

It looks like 60C starts killing off weed seeds.

[rary]

Since I posted this question I have been giving it more thought, it basically is the weed seeds I want to kill off, I am not looking for completely sterile compost, (if its completely sterile is it still compost or just a bulking agent? ) but as I now intend using my home made compost mixed with sterilised soil in my flower baskets, I should be able to control any weeds when in such small areas, but interesting to know others thoughts on this, so thanks for replies

Just to add as Nicos has pointed out insects etc. would be killed off at 40c which no doubt would include worms and having experienced flat worms I don't want to reduce the worm population, other than flatworms

[mrsbusy]

Can't you just hoe off or pull up the seeds that germinate or cover the compost with something to exclude light so the seeds cannot grow.

[rary]

I had been thinking of using my home made compost for my flower baskets, as I use quite a lot of compost for that, I think most of the the peat free compost that is sold nowadays comes from bulk composting where high temperatures are generated, I don't have the high volume of material required for that, nor am I able to turn compost regularly, I use bins the size of wheel bins and once full I push a brush shaft down into it to allow air access, it's slow but it works, though temperatures never get high enough to kill off all weed seeds, hence the thought of sterilising it, but in the long run I think it would do more harm than good, I have now added my own compost to purchased compost and will be doing as you said and remove the weeds as they come through, this post has made me think on why there are so many complaints about the peat free on sale now, peat is a sterile medium as far as weeds were concerned but wonder if all the microbes etc. which are required for things to grow are more prevalent in peat, when heat is not required, no doubt someone will be able to answer that, by the way peat based compost is still available in Scotland, but I think its important to save the peat bogs

[nvidura]

I’ve tried sterilizing homemade compost in the past to kill pests and pathogens. While it does eliminate harmful microbes, I found it also kills beneficial ones, which reduces the compost's effectiveness for plant growth. Steam might be a gentler option than dry heat if you want to preserve some nutrients, but personally, I’ve opted to focus on keeping compost balanced with good aeration and moisture instead. If your compost is healthy, sterilizing may not be worth the trade-off!

[Vince G]

Does the heat in the compost heap not mean that it sterilises itself?

[ChingfordHarry]

Does the heat in the compost heap not mean that it sterilises itself?

Probably not, unless you have something like an insulated compost bin, which can maintain a temperature high enough for long enough. Insulated bins don't come cheap, though.

[Penellype]

Probably not, unless you have something like an insulated compost bin, which can maintain a temperature high enough for long enough. Insulated bins don't come cheap, though.

Even with a hotbin composter there is plenty of life in there. Mine gets to over 60 degrees in the height of summer when grass is a frequent addition, but as it cools down a bit in the autumn you see all the life coming back. There are masses of small mites, often mould or even fungal fruiting bodies, sometimes loads of worms. The heat itself is produced by bacteria, which by definition must remain alive in order to keep the heap hot. Most seeds are killed by the heat, but tomatoes tend to survive.