How do you sterilize used compost

[Scoot]

I understand why you want to do it Rary as it seems an expensive waste. And there are soil sterilisers for gardeners - e.g. at
Soil Steriliser : Two Wests and Elliott
(that claim to kill off the bad guys and save the good guys....).
But they're expensive and I imagine will send your electricity bill sky high too.
The amount of energy required to sterilise soil would be worrying too on the climate change front if everyone started doing it..... And I certainly wouldn't want it in the oven or microwave!
I've tried re-using compost for (local) show potatoes with generally disastrous results or supplementing new compost with well-rotted manure (not so disastrous but manure can cause staining on the skin so not perfect either...). So now each year I use the previous year's "spent" compost as a mulch or general soil conditioner elsewhere and face the cost of buying afresh.... I guess any hobby has a price! Clearly the cheapest way of doing it is to give up the hobby!

I have also tried using old compost with very mixed/bad results. Next year I'll still use it but I'll be using it with homemade compost and as you say, facing up to the cost of buying fresh compost to get better results.

[Potstubsdustbins]

I used to give a nod to rotation by using compost for different things every season, now to be honest I don't bother.

The compost with heavy root growth goes in the dalek to help that along. The rest is stored over winter in dustbins etc where the frost can get at it, a good frost works wonders. Come the next season its riddled, nutrients are added and away we go.

There are two exceptions (1) If I have any disease problems, that gets sent away for recycling by the council. (2) I always buy a small amount of new compost for seed cutting.

[Penellype]

I have a used compost mountain problem because I grow most things in containers and almost all my bare soil is mulched so I don't really have anywhere to put spent compost. I use new for seeds and potting up small seedlings, to give them the best chance in life. I also use new for any plants like tomatoes that are going to live in the house, as I am not keen on wildlife on the windowsills.

I'm attempting a rotation system, which involves painting numbers on buckets and keeping a list of which bucket grew what and when, mainly because I have had several disease issues this year, particularly with potatoes (which account for more than half of the buckets). The potato compost will be sieved and used for growing carrots or brassicas, the chunky bits will be used as bulking agent (necessary) for the hotbin. As many as possible of the potatoes next year will be grown in compost straight out of the hotbin, which is supposed to kill most diseases and pests when running at above 40C (mine is currently at 65C). The remainder will be in compost which was used this year for carrots, cabbages or courgettes. Having experimented this year with adding bfb/not adding bfb, feeding with liquid feed and not feeding, I will definitely be doing both of these, although the hotbin compost + bfb gave much the biggest yield this year.

There was one instance earlier this year where I had a real problem with pests. I had a bucket of chinese celery which was starting to bolt and was covered in aphids. When I had removed it there were aphids of various sizes all over the bucket and compost and there was no way on earth I could remove them all by hand. I wanted to plant summer cabbage in there, so I boiled a kettle and poured a couple of litres of boiling water over the bucket and compost, then left it a day or 2 and inspected it for aphids. I couldn't see any, so I planted the cabbages and they were fine.

[Aberdeenplotter]

I normally chuck my used composts including that used for toms and spuds in the bottom of my pea and bean trenches where they are brill for holding moisture. If I felt the need to sterilise old compost, I'd give it a drenching of thick bleach(my preference is domestos) in a solution with water. Bleach of course is an oxidant.

[BUFFS]

Thanks bazzaboy, electricity wouldn't be a problem as I have solar panels, and a low power usage during the day, but the cost of the sterilazr is a bit on the high side, but I do have a wood burning stove, on which I can sit a pot on and heat up the compost, but one of my concerns is of the change to any chemicals that will be in the compost from unused feeding as heat is applied to it, it may be unfounded, or it may be more bother than its worth to make it safe

I hope you sprinkle the ash from your wood burner onto your soil, or that would be a waste..

[Penellype]

If I felt the need to sterilise old compost, I'd give it a drenching of thick bleach(my preference is domestos) in a solution with water. Bleach of course is an oxidant.

I'm sure most organic gardeners would cringe at dousing compost with concentrated sodium hypochlorite solution, although to be fair we probably all drink some of this in our chlorinated tap water every day. Its a fairly nasty chemical - from Wikipedia:

"Sodium hypochlorite is a strong oxidizer. Oxidation reactions are corrosive. Solutions burn the skin and cause eye damage, especially when used in concentrated forms. However, as recognized by the NFPA, only solutions containing more than 40% sodium hypochlorite by weight are considered hazardous oxidizers. Solutions less than 40% are classified as a moderate oxidizing hazard (NFPA 430, 2000).

Mixing bleach with some household cleaners can be hazardous. For example, mixing an acid cleaner with sodium hypochlorite bleach generates toxic chlorine gas. Mixing bleach with amines (for example, cleaning products containing ammonia or related compounds and biological materials such as urine) produces nitrogen trichloride.[18] This gaseous product can cause acute lung injury. Chronic exposure, for example, from the air at swimming pools where chlorine is used as the disinfectant, can lead to the development of atopic asthma.[19]
...
Household bleach and pool chlorinator solutions are typically stabilized by a significant concentration of lye (caustic soda, NaOH) as part of the manufacturing reaction. Skin contact will produce caustic irritation or burns due to defatting and saponification of skin oils and destruction of tissue. The slippery feel of bleach on skin is due to this process."

One of the reasons for growing my own veg is to avoid this sort of thing...

[KevinM67]

Christ Penellype !!!

I'm never cleaning my toilet again.

[rary]

The strength that AP is useing is very weak as houshold bleach is a 5% solution then added to water reduces it even more, but always use a clean plastic container or bucket, never a galvenized container,and add the bleach to water not water to bleach, and keep your face well clear while doing so

[Potstubsdustbins]

For many years when on the tools if my hands got really dirty I would just use house hold bleach to clean them and rinse them off under the cold tap.

Not recommended for people with tender skin or allergies.

[Aberdeenplotter]

Its a fairly nasty chemical...

It's such a nasty chemical it's the main source of chlorine used in swimming pools where even babies are immersed in the water. The OP didn't ask for organic methods of sterilising his pre-used compost. The object of sterilising is to kill pathogens and organisms likely to cause damage to growing crops.. Rary correctly says that the solution in the product I mentioned is already diluted and of course I did say that I would be using the product further diluted in water and not using a concentrated solution sodium hypochlorite as you imply in the first sentence of your post.

[rary]

You are correct AP, I didn't ask for organic methods, and having worked in a process where bleach was made I know some of the dangers of using chemicals, and if I remember correctly formaldehyde used to be used for sterilizing soil, I think I would stick to bleach, but I asked in a previous reply if there are any changes/dangers of heating it up if there are chemical feeds in it and I was thinking of dangers to myself and the plants, perhaps for the next growing year I will switch the flower compost with the veg material, but that's just putting the problem back to an other year

[BUFFS]

i know some gardeners that use ***** fluid on their greenhouse soil in November each year, a good soaking, and they reckon it clears the bugs, no intention of trying it myself as I have the garden ticking over without using any chemical nasties, one has been doing this for years and I don't suppose he will ever change but I wont be eating any produce from that source..

[Jungle Jane]

I wouldn't use bleach or any chemicals on the soil because there are better ways. Babies are in a chlorinated swimming pool learning life skills for about 20 minutes & showered straight after or their skin would be extremely dry & dehydrated,some children come out in a rash because of the water even showering straight after & they have to use cream,probably a steroid cream for skin conditions but I'm not 100% certain it affected my daughters friend when they used to go swimming with the school,it's the only choice you've got if you want to go swimming. It's different to using bleach in the soil because there's other choices or you could wonder why don't parents sterilise their babies feeding equipment in bleach & use sterilising tablets instead? If you had a skin or breathing condition caused by bleach at our age,how can you prove it was the chemical that caused the illness? If crop rotation is used you shouldn't need to clean the soil,can you replace it with clean soil unaffected by blight from somewhere else? For people who don't use chemicals it's a little bit worrying to read but everyone's different & has different opinions so it's good to hear lots of different viewpoints.

[MarkPelican]

, perhaps for the next growing year I will switch the flower compost with the veg material, but that's just putting the problem back to an other year

By this statement, I assume you have pots with flowers and pots with vegetables (mainly tomatoes and potatoes of interest to this thread). The biggest problem I can see, rather than a build up of viruses would be things like vine weevil. So a help would probably be to spread it out and allow the birds access to rootle through and take out nasty things. Possibly also mix both sets of compost together.

I always use new compost for seedlings and half fill my buckets with riddled refreshed compost, topping them up with new compost. I've never had a serious problem.

[Penellype]

It's such a nasty chemical it's the main source of chlorine used in swimming pools where even babies are immersed in the water. The OP didn't ask for organic methods of sterilising his pre-used compost. The object of sterilising is to kill pathogens and organisms likely to cause damage to growing crops.. Rary correctly says that the solution in the product I mentioned is already diluted and of course I did say that I would be using the product further diluted in water and not using a concentrated solution sodium hypochlorite as you imply in the first sentence of your post.

Sorry, didn't mean to offend.

Quite often chemicals are used to kill bugs as a "best of evils" scenario. This is true of chlorinating swimming pool water, the preservatives used in meats like ham etc and various other things that we meet in everyday life. The alternative is to risk getting nasty infections or food poisoning from the bacteria that these chemicals are there to kill.