how to sterilize perlite?

Floyd, VA(Zone 6b)

I have been modestly successful this spring rooting NZ impatiens, coleus,
and bee balm, and brugmansias in moist perlite. Now I think I need
to sterilize it before I try anything else. I think it smells a little off. How
can I sterilize it?

Barmera, Australia

Depending on the amount you have but for a small amount, make sure it is damp put into a sealed plastic bag and place in the oven and heat to 60c and hold it at that for 30mins. Or put in an oven set at 100c and leave there until heated right through plus an extra 5mins. As you will appreciate the thinner the layer of perlite the quicker it will heat through. Another more messy way is to put the perlite into a bucket or tub and cover with hot water from the household system assuming your system is set at about 70c that should be sufficient to steralize if covered and left until cool.
I'm not familiar with your climate but if your daytime temps get into the mid to high 30c you can put the perlite into a sealed clear plastic bag and leave in the sun this will get hot enough to steralize the material. It is called Solarisation and you might like to check that out to see if it suits you.

This message was edited May 19, 2009 9:38 AM

(Sheryl) Gainesboro, TN(Zone 6b)

I'm betting that Brian's last suggestion is the best - that or washing it in a bleach sol'n, 10 parts water to one part bleach. But unless it's discolored, just drying it out will probably do the trick.

Nurmo, Finland(Zone 4b)

I've never thought of using perlite twice. Just chucked it out and bought some more! Thanks for the idea. Of course perlite, unlike vermiculite, doesn't absorb water, does it. I'm not so keen on using bleach though. Some plants would be sensitive to even minute residual traces.

Floyd, VA(Zone 6b)

Since I had to bake anyway, I popped an aluminum pan of it as the oven heated up to 350 F. I took it out as soon as it got hot and let it cool off.

Now, I am wondering if I should use it for rooting cuttings. I have a sterlite shoebox with the perlite in it. If I drill holes in the top,
I could put the cuttings down into it. OR I could reduce the amount of perlite,put a lot of water in the box, and submerge an air stone into the box. Then I could put the box on a heat mat.? I would probably put a little peroxide into the water now and then. If I do this, the cuttings would suspended just above the water so the roots would reach down, maybe?

Richmond, TX(Zone 9a)

gloria I was intrigued by your question as it never occurred to me to recycle perlite. Perlite at the feed store is cheap in my area so not worth the trouble of sanitizing. However, if sterillizing makes sense for you and others, there is a good article appearing in the LSU Ag Ext. website. I googled "reusing perlite" and the first hit was an article by the LSU Ag Center, but it wouldn't let me link here. Worth reading.

I throw my used perlite in existing beds and so far, no problems.

Floyd, VA(Zone 6b)

Vosner, Thanks for the link. Not only can it be recycled, it is actually better than new!

Sifting, cleaning and disinfecting used perlite for recycling saved 56% of the cost to replace the media and reduced salt content to the optimum level recommended for raising container grown plants. Disinfecting used perlite with hot water raised media temperatures above limits necessary to kill several fungi and nematodes. Tomatoes planted in recycled perlite produced greater marketable yield and heavier fruit than those planted in new perlite. Used perlite can be cleaned and disinfected as needed and recycled for many years because it is not organic in nature and is physically and chemically stable.

Barmera, Australia

You seem to be well on your way to reusing your Perlite but another thought. If your heat mat can be set to 140F = 60c and your perlite placed on that until heated right through and kept heated for 30 mins it will do the same job the snag is of course that you can not have plants on the mat at the same time.
Regards Brian

Hendersonville, NC(Zone 7a)

This thread reminded me of when my father nominated me for the job of sterilizing the soil he used to start plants. I know for certain that he would never have bought DIRT -- not when we had it for free! Although I recall him having bags of what must have been either perlite or vermiculite which was mixed into the garden. Actually the soil was way "too rich" and needed builders sand added -- we had mucky swampland. I recall him testing the pH and adding lime. It's weird what I recall from 40 years ago.

I vaguely remember the instructions given to me --
get large oven-proof pots
fill 1/2 full
bake at ???? (some forgotten temp)
bake for ?? minutes (I think my dad used a temperature probe to figure out how long it took to get "up to temp")
(considerably less than 350, probably 200-250)
allow to cool
dump into special (sanitized) buckets provided
thoroughly clean pots when finished (mom's instructions, not dad's)

I recall him using this sanitized mix to start tomatoes -- otherwise the seedlings got some type of withering at or near the soil-level. Seems like plants which were "started" in non-sterilized soil started out looking fine and then withered at the soil-line and then sorta tipped over.

Oh well, that's how I remember it anyway. I also remember that I steered clear of the topic of my new "weird" chore with my friends. I envisioned the conversation as: What did you do this weekend while we were at the beach? Uh, I baked dirt and then baked some more dirt, wanna try some?


Kerrville, TX

I believe the hydroponic folks sometimes pour a weak solution of hydrogen peroxide through the perlite.

(Clint) Medina, TN(Zone 7b)

I always just root coleus in a glass of water in the window. I've never had one fail. That method can't be beat in my opinion in coleus plants.

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