Sterilizing growing medium

[InspirChid1712]

I have a large bag of bark that I use for potting, but I made the mistake of leaving the bag open outside this summer. Now I have noticed white fuzz growing on the medium of the plants I have already potted with it, so I believe it is contaminated with mold spores. It doesn't seem to be harming the plants, however. My cattleya is really in need of repotting, but I it appears to have some sort of moldy plague as well, and I want to be sure the new bark is sterile before repotting. Any ideas on how one goes about sterilizing the medium?????

[kavanaru]

Hi Elliot,

I am not an expert in the field, but there is something we use to do in the lab in order to sterilize media that was possibly contaminated with fungi. Especially in those cases when we did not wanted to use chemicals... Just give the media a long bath (one our or so!), then drain it and let it rest covered for 12 - 24h(better overnight - this humid rest will activate all fungi spores, and possibly some dormant bacteria) then put it in the oven and 150 - 180ºC for 30 - 45 minutes, in order to kill all fungi and bacteria. You have to take care it does not burn and from time to time just move it thoroughly to have all media heated in the same way. Since you activated the spores before, you can be almost sure you will have no heat-resistant spores waiting to givve you a surprise later

I have never tried this with orchids... but it could work

[quiltergal]

You could try pour boiling water through it.

[kavanaru]

pouring boiling water would not kill heat resistant spores! fungi spores are normally very resistant to different kinds of stress (e.g. heat, drought), and they can stay dormant for years... you need to reactivate them (allowing them to germinate in a convenient environment) in order ti kill them without strong chemicals... allowing the media to rest under these conditions for 12 - 24 hour would be long enough to achieve the goal, but without letting the new growth mature and produce new spores...