First off the used potting soil went through my compost screen to remove all roots, leaves, maple keys etc. With that done, place the potting soil 4" deep in a roasting pan that is not used for food. Top it with foil to seal the moisture in and then insert a thermometer to monitor the temperature. Then the whole lot went into a 200f oven.
Now monitored the thermometer until it reaches 170f, it took a good hour to heat to this point. Once at 170f hold the temp for 30 minutes which is long enough to kill off any nastiest and weed seeds.A few words of caution: One, it kind of smells, but not to bad. Like an earthy peat moss smell and it does not linger. Two, it is important to not heat the soil over 200f or it can create toxins that will kill your seedlings. Make sure to monitor the thermometer. Three, this only needs to be done for seeding, for potting up you can just screen the soil. All in all it was a pretty painless procedure and saved buying a $10 bag of seeding mix.
I keep thinking that I need to do this with my garden soil. I brought in a bucket for my soil block mixture. I ought to sterilize it. I really should. I just worry about the smell. I ought to just do it one day.
ReplyDeletethis is very interesting. i'll have see if my mom has a big roasting pan to "loan" me! (well it wouldn't be right to give it back after i cooked soil in it! =)
ReplyDeleteOh no! Think of all the innocent little bugs that got fried in there with it !
ReplyDeleteKidding. :)
I'm not at the soil recycling stage yet. Any used potting soil gets put into the garden. (Any bit is useful to amend heavy clay). So (for now anyway) I don't mind buying new each year. I can see why sterilization is important for seedlings. Nice post !
Daphne - It really does not smell that bad. The smell of boiled eggs is worse then the smell of cooked dirt :-) I did it in the evening and within an hour there was no smell left.
ReplyDeleteKelli - Yeah, dirt and food really don't go well together :-) Although it is probably overly cautious to not use it again.
Miss M - I used to just add the old potting soil to the garden as well. But when I started adding it up I was going through $50+ worth of potting soil a year! Now I have 4 huge bails worth behind the shed to reuse. Thankfully only the soil intended for seeding needs sterilizing.
Dan, I learned a nifty trick that cuts down on the smell factor, roast the soil in a turkey roasting bag. It doesn't totally keep the smell out of the kitchen but it does reduce it a lot. You can either pierce the bag with the thermometer or close the bag around the stem and seal it well. The bags can be reused.
ReplyDeleteI had asked about this a while back on the container forum, but nobody gave any good answers. I intend to do the same thing with my earthtainer soil. Thanks for posting about it.
ReplyDeleteI generally mix my own potting soil so I don't sterilize and reuse. I have such terrible soil in the garden beds that I use the potting soil as mulch at the end of each season. Mixing your own potting is a great way to save cash - I could never pot as much as I do without doing it myself.
ReplyDeleteThank you, Dan. This is a saver! I think John Best has an old microwave that he uses. Either way, I'd sure like to be able to reuse some of my potting soil.
ReplyDeleteMichelle - I will have to look for turkey bags, never heard of them before.
ReplyDeleteEG - You can cook it on your grill as well, it would just need alot of attention so it doesn't burn.
Chiot's Run - I have thought about make my own mix but have yet to find pearlite or vermiculite in bulk at a good price. I have about half a cubic yard of saved potting soil now so I should be good for a while.
Granny - I read about the microwave method too but you can only nuke a small amount at a time. We also rarely use a microwave so ours is only 700watts. In the oven I did about 3 gallons in two batches.
Very frugal Dan. I reuse my potting soil for at least one year and then rotate it into the garden and buy new. On the germinating mix, I buy new each year but I really might consider doing the sterilization thing to get more use out of it as well.
ReplyDeleteOkay... that was me on the previous post. I got too quick with the "publish your comment" button clicking!
ReplyDeleteI would have never thought to do this, but it does seems awfully wasteful not to reuse last year's potting soil. I'll have to keep this in mind.
ReplyDeleteThe only reason I would have put it in the oven is to get rid of noxious seeds that have invaded the Midwest lately. Otherwise I would have put it in a tupperware and left it in the hot and cold outside to naturally kill seeds until I could use it.
ReplyDeletePotting soil requires some bacteria and mycorrhiza to chelate nutrients and prevent disease, which is why I supplement with Subculture B and M from General Hydroponics. As always, your mileage may vary and I hope your method works well for you.
This is great information, thanks for sharing it. What away to recycle. I have been throwing it in my compost bin and reusing it that way, but that is for the outside garden, nothing was avaialbe for seed starting mix other than store bought.
ReplyDeleteI'm doing this!! I looked up an article a while ago about this and I wanted to do it but got scared. Seeing this post reaffirms that I was on the right track.
ReplyDelete