I need some advice. I have a bag of what I consider my favorite and best potting mix. I always use it for sowing seeds. It's a bit more expensive than other potting mixes. I have a bag that has been opened but was kept closed in my garage for over month. I want to use this bag for seed starting but am worried about gnats especially gnat larvae that can destroy sprouting seeds.

I have an old microwave that we were going to throw out but forgot to. It is also in my garage. It still works. I had read about sterilizing potting mix in a microwave. So I would like to try that. What I need advice on is HOW to sterilize potting mix in a microwave oven.

What do you put the potting mix in to cook it in the microwave?

How long do you cook the potting mix in the microwave to kill any bacteria, fungus, or bugs? I want the mix sterilized for seed starting.

I have perlite in this potting mix. Would that cause a problem when heating the mix in the microwave? It wouldn't explode or anything, right?

Do these 2 instructionals seem accurate?

http://homeguides.sfgate.com/m...

http://www.momsbudget.com/cont...

I am still worried about how the perlite reacts to extreme heat. Anyone have any experience doing this?

Hmmm... I don't know about the perlite - perhaps someone else can speak to that. I have microwaved soil-less mix without it before and really what you're going for is heat. I wet the mix (not sopping wet but damp) and put it in a pyrex bowl (easy enough to clean afterwards) and into the microwave. I zapped it on full power for 5 minutes, mixed it around, then 5 more minutes. It will be HOT HOT HOT so be careful.

Another option is to water with dilute hydrogen peroxide but that was unsuccessful for me.

The other, likely easier option, is to top with something like gnatnix or water with some gnatrol. I have done neither of these but perhaps one of these two ( @Ahead @Nysbadmk8 ) can answer any questions you may have about that.

James - I purchased some 1.oz (28g) Gnatrol OMRI selective biological larvicide for Fungus gnat control this year but have not used it because I didn't know how it would affect germinating seeds. Plus there was no label on the container and I can't find the instructions that came with it on how to measure and use it. But I have some. I just didn't want to kill my very young seedlings with Gnatrol.

Becky, here's an article by North Dakota university extension that has a paragraph of instructions for pasteurizing in a microwave:

https://www.ag.ndsu.edu/pubs/p...

You could test the mix for fungus gnat larvae by placing some sliced potato on it and checking under the slices in a day or so.

The label for Gnatrol should be easy to find on Google, just type in: Gnatrol msds label

I wouldn't be too concerned about perlite although I don't know for sure if it would be a problem in the microwave, since it is heated volcanic material in the first place. I would make sure it really is perlite and not polystyrene though.

Thanks, Sue! I will check out that link. I also found my old email from the seller of the Gnatrol so sent an email asking for the instructions. Either way, I am sure I can get them. I just do not know how safe Gnatrol is with sprouting seeds? Anyone know?

Sue said, "I would make sure it really is perlite and not polystyrene though." Good point!

Why is it that my name is associated with gnats?

Becky, I never nuke. I use gnatrol, and have for a million years. I like to keep things simple....for obvious reasons....lol. When I plant my seeds, I use a mixture of water and gnatrol for the first week or so after planting. It has worked very well for me.

Steve - Thanks!

Now to find the dosage amount and instructions on the use of the Gnatrol dry powder that I have.

Becky,

I buy new every year...seems to lose it's strength the second year.

Happy germination!

Where do you buy it?

Amazon.

Thanks

This seller?
https://www.amazon.com/dp/B003E7BGTU/

I bought mine from someone else on Amazon. I read that the powdered/granule form can last 2 years. Liquid form only lasts 1 year.

Steve - Do you use the liquid form or the powdered form?

I use the powder form.

Do you remember how to mix it? I haven't found the instructions and the seller has not replied to my email.

This is off an old jar. I never measure, but here's the label:




You need to click the image to read it.

Steve - THANK YOU very much! That's exactly what I needed.

No problem, Becky. Good luck!

Lisa, I couldn't tell you...but I never got it that cheap!

My newest bottle has an expiration date, and was for a larger quantity.

Becky, there's a specimen label for the WDG form here so that you can read the precautionary statements:

http://www.valent.com/Data/Lab...

Sue - Thank you for that link.

Yes, I figured it was toxic. I don't really want to use it, but was planning to use it as a back-up plan if sterilizing my potting mix didn't work.

I am still determined to sterilize the potting mix and will be doing it trial and error following the links in my second post above. I did dose the current seed cups with H2O2 & water twice when I planted the seeds in them and am hoping that may have helped to kill any gnat larvae. But I will try the gnatrol if I have a problem and mix it outdoors since I do have 4 pets. I am an organic gardener, so chemicals go totally against my gardening style.

The other problem that I have is the potting mix I love is sold at a nursery and stacked outside. The bags have air holes in them, so they may come with gnat larvae already in them. (And I suspect as much.) So I definitely need to figure out a way to sterilize the mix. I can't find this potting mix anywhere else locally. But .... it is such a good mix, that I am willing to try sterilizing it myself!

Thanks for everyone's help!