Hi all! I have recently started propagating some of my seedlings in a “sterile” perlite/peat mixture. This worked very well for me, but I noticed at the end of the season that the perlite was covered in green algae. Do any of you have any experience reusing propagating mixtures? Would it be helpful to disinfect the mixture with say peroxide or sodium percarbonate?
What are some thoughts?
Are you propagating indoors or out? If outdoors, just reuse the perlite. I’ve reused green perlite outdoors for 30+ years with no apparent issues. Indoors, I don’t know whether it would detrimental or not.
Could you try microwaving the medium if you want it sterile?
I’m not sure how safe microwaving perlite, vermiculite and other materials in the soil mix may be. Baking or steaming it would kill pathogens. It would definitely stink, but it would work.
No microwave for nuking the medium, I don’t own one. I’m sure the peat portion of the mix would be fine with this treatment, but I don’t know about the perlite.
It is outdoors. It is encouraging to hear you’ve had no issues with green perlite. I had thought the medium needed to be sterile, or pretty near to curtail any tendency for the cuttings to rot. Perhaps it’s okay so long as there is good drainage?
Perhaps sterility may be necessary indoors where conditions are more conducive to rot taking hold, but outdoors, “in Nature”, there is no such thing as “sterile”. All the fungi, bacteria and plants evolved to work together and there are sufficient other factors to keep them all pretty much in balance. Drainage and the friability of the medium are probably two of the more important factors. You need moisture retention while providing good drainage in a medium light enough not to inhibit small seedlings from pushing through it.
If you try to microwave vermiculite, keep an eye on it. I believe it is expanded mica, which might create a bit of a show in the microwave. (I am probably wrong, but mica is quite shiny, and as a dumb kid I recall creating some spectacular fireworks putting shiny things in the microwave.)
I wouldn’t reuse it. I have had lots of problems rooting in reused medium. I’ve also had problems with buying bags of potting soil that are excessively wet when you buy them. I always use new medium for rooting. Reuse that old medium repotting older plants. Especially this year my supplier of bagged soil has been shipping out medium bagged when it was wet.
Did you have problems with rotting or fungus? I wonder if the peroxide treatment would take care of this?
Every year I have some problems with rot. I had more trouble this year I believe because the potting soil I use was being packed when it was wet. It was wet, heavy and compacted in the bag. That gives bacteria or pathogens conditions to thrive. Also, when I reused potting soil that I had used before, almost everything rotted. If you buy potting soil try to choose bags that are light and fluffy, not heavy and wet. I do use pure perlite and have great success because it’s sterile. So if you’re having trouble with rot and I need a sure thing, try perlite. Good luck to you!
There are beneficial microbes in healthy soil than can mitigate risks (search for organic control of damping off to find commercial available inoculants, which I need to obtain, I am reminded) which, much like probiotics in our gut, prevent bad guys from overruning the system. I have actually wondered if sterilizing media opened the door for the bad actors for me the last few years (much as a long run of using antibiotics can open the door for e.g. a C. difficile infection.) The products can be pricey, but allowing media to mellow in a happy environment (someone suggested with a little fish fertilizer) seems to mitigate risks in aged media by encouraging beneficials.