compost sterilization

[John85]

what method do you think is the best?
pasteurization at 70 C to spare some good fungi
sterilization at 90 C to kill everything
drenching with boiling water for surface sterilization
microwave but it is said that it does not kill weeds seeds and release easily toxic substances
please let us know your practical expiriences and  ........failures.

[Maggi Young]

Hello  John,
I'm not a great fan of sterilising compost.....though some folks do so all the time..... I worry that there is more dmage from removing "good" bugs/fungi than there is from the "bad" bugs/fungi. I alos fear that any detrimental organisms are likely to re-colonise the mixture a lot faster than the "good" ones... so, I don't bother.

I can tell you that the stink from sterilizing compost in the microwave is really horrible!

[Martinr]

I sterilise my home compost at 95 C to kill everything but....this is only because I build enormous cold compost heaps which don't heat up very well and use my compost as a mulch on borders. If I don't sterilise it I end up with lots of weed seed germination. I do the sterilisation in a large electrically heated container I bought from Two Wests & Elliott.

[John85]

Maggy  Using vapour is also very smelly but much slower and uses more energy (I think) but may be better  for the plants .I have to do it as the compost I buy from the local council is full of weeds.The one in bags you can buy here is not better.Weed free but made from a bog(carex and juncus)peat not sphagnum peat.It has no structure and makes an awful sludge when wet.
how long do you simmer the compost.I know it is important not to "overcook"

[John85]

Thank you Martin.Can you give me some more information please?What is the capacity?How much Watts or Amps?One orthree phases?And a rough idea of ....the price.What is the type and brand name ?

[Susan Band]

Hi John,

I used to use a steriliser when I used my own soil in my potting mix in the days I potted things up. The one I used must be at least 30 years old but they still sell them at LBS, they are featured in their wholesale catalogue so they would sell them even although they weren't on their retail website. They take at least 1 1/2 wheelbarrow full, I think it was the 68L size I had and cook for 1 1/2 hrs. A bit expensive to buy but I does get rid of the weed seeds, I you want you can buy beneficial fungus to add when making the compost. I used about 1/3 soil 1/3 peat 1/3 grit with long life fertilizer.
Hope this helps.

Susan

[Martinr]

John, Two Wests sell 2 sizes. 34 litre uses 1.5KW and current price is £365. The 68 Litre one uses 3KW and is priced at £575. Both are single phase plug into your domestic mains. Mine doesn't have a brand name on it but if you Google Soil Steriliser you'll find other suppliers of the same units

[Martinr]

John, I've just looked at your profile and suspect you live on the other side of La Manche (forgive me if my schoolboy French has got the gender wrong). The units are 240V, 50Hz so should be OK in France.

[John85]

thank you Martin.You are right.It is La Manche but where I live it is the Atlantic Ocean that is close.Do you also 'cook' for 1 1/2 hour?May be earth takes longer than compost as it is more compact?

[Martinr]

The steriliser has a thermometer, you cook till it reaches 95 C and then dump the results through the bottom. It takes about an hour to an hour and a quarter.

[John85]

thank you Martin.I had a look at Google like you suggested.Interesting!I was surprised that there seems to be no water container at the bottom to produce the vapour like in the very big ones I saw at nurseries.Is the resistance in direct contact with the compost?How wet must it be?Just like for potting up a plant or wetter?

[Martinr]

John, I take it straight from my compost heap and into the steriliser. The heating plates are in direct contact with the compost and it relies on there being some moisture in the mix but I've done some loads I thought might be too dry but been amazed by how much steam appears towards the end of the cooking.