Re-using potting mix.

[Redsonic]

Many infections common in medical situations have been bred tough by inadequate controls so they are now tougher to kill. Same thing has happened in sgriculture with weeds and pests becoming resistant to some chemicals and treatments - Warning to bonsai growers who don't sterilise properly.

The reason why medical equipment needs to be autoclaved at 120 degrees or more (with moisture and pressure) is because some bacteria can form a spore (an inert form, encased in a very tough membrane). The spore is super resistant to heat, drying, steam etc. Once conditions improve, the spore becomes a bacteria cell again, and can infect the patient. Bacteria have always been able to do this; it has nothing to do with selected resistance.
Anything we are doing with stove or microwave is sanitising, not sterilising.
If you really wanted to whack your mix, you could buy an old stove top pressure cooker, wet your mix, and get it over 110 degrees for 10 minutes. You can buy special autoclave indicators that change colour to tell you that your sterilisation has worked.

[Robsterios]

I re-use my potting mix...but not for Bonsai. I just basically grab out any major roots or screen roughly and use it for the garden as a top dress under mulch. Great for the garden, particularly if using quality components like pumice, zeolite and such.

[Sno]

Has anyone found if boiling or cooking substrates make them less stable ? Especially Diatomite .
Cheers Sno

[Graeme]

My method of sterilizing soil is cost free, although it takes a bit longer than the other methods detailed here. So, once all the repotting is finished I sieve the soil, getting rid of the fine stuff. What's left goes into clear plastic bags, I use the largest ziplock bag I have found in the Supermarket. I fill each page about 3/4 full and seal up. Once all the soil is bagged up I spread out a piece of black plastic and then lay each bag of soil out on the black and flatten it out as much as possible. then I spread another sheet of black plastic over the soil bags and weigh that down with bricks etc around the outside of the sheet. This is done in a place that receives the maximum amount of sunlight. The soil then remains undisturbed for as long as possible, definitely not less than a week. the bags of soil I then simply store in the shed until they are needed again, when I add a little extra potting mix as required. Kills most pathogens, virus and grass seeds as well.

[hawkeyes]

Graeme, that sounds feasible, good ideas in this post.

[GavinG]

I have far too many trees, and I can't afford fresh pumice/diatomite for the lot each year, so I dry it out in mid-summer, sift the fines, and re-use. My main point is: NEVER EVER re-use soil from a pot in which a tree has died. Routine re-pot yes, diseased tree no.

Straight into the garden.

Gavin