Questions : reusing potting mix from one type crop to anothe

Crestview, FL

My 6 totes of onions were done and I pulled them up. I had already started my potatoes in smart pots, and decided to use the potting mix out of the totes I had grown my onions in to hill them with. My sis came over to help me finish hilling them and filling the smart pots up with potting mix from the totes where I had grown my onions in this past weekend. She mentioned to me that she saw a fast moving red worm in the potting mix she added to the smart pot, she said it was long and skinny. Should I be concerned? I figure my potatoes will be ready for harvest in about 2 - 3 more weeks at the most. But, does using the potting mix I grew yellow Texas granex and GA white sweet onions to hill my potatoes put my taters in danger at all I wonder?

Charlotte, NC(Zone 7b)

joy - do you think that was an earthworm? If it was, no worries.

As to reusing potting mix - I do it all the time. However, if you've had plants with diseases in any potting mix, you might want to throw it in the trash rather than risk spreading the disease around.

Kerrville, TX container gardening, I re-use my in-organic potting mix and have done so for a few years now. But the key word here is "in-organic" such as a coir-perlite mix or perlite-vermiculite mix. None of that nasty old dirt or organic stuff like cow, horse, chicken or any other kind of poop. Some of that organic stuff tends to get slimy and pack down and closes off air flow to roots and get stinky. Peat moss tends to become brick hard if you let it dry out and can become very hard, if not impossible, to re-hydrate. Coir will re-hydrate after drying out. I have used some peat mixes from year to year but they were heavily modified with per-lite and stored slightly moist in trash barrels. Back in the old'n days, when I was going organic, I also re-used grow mix by putting it in a compost pile and adding new stuff to it over the winter and adding stuff like bark fines and per-lite to it to make sure its structure stayed open enough to allow aeration of root systems.

This message was edited Apr 30, 2010 6:19 PM

Crestview, FL

Jaywhacker: Hmmm, thanks for that bit of information, I stayed away from the coir with the potatoes, because I didn't want them to rot, started with garden soil and compost (black Kow to be exact) and wound up topping off with potting mix and perlite. The onions were done with the Jungle Grow potting mix; but, it wasn't the new kind they have out that is organic with neem in it, I did buy some of that, so will dump that after this season since it is organic. I suspect I will having taters around the middle of May as they are starting to flower and the smart pots are topped off, wish this weather would let up though.

Pine Island, FL(Zone 10a)

In the past, if I haven't been able to fish out the fertilizer in my used potting mix, I've just added the whole thing to the compost heap. Now I have so many planters and buckets I don't want to keep buying the mix, so if I re-use it, how do I keep the accumulated salts and unused fertilizer from damaging the plants? Also, since it's year-round gardening gardening here the old mix never gets a chance to dry out, get sun-sterilized or anything like that. Is that a problem? I don't want to plant seedlings in the old wet mix and burn them or worse, subject them to some rotten pest that is living in the mix (like cutworms or something).

ALSO, since my main problem is probably fungal in nature, I don't want to force my little babies to fight for their lives right off the bat. Any suggestions would be appreciated.

fyi, a drop (one drop) of Ivory a gallon of water will do wonders re-hydrating peat moss.

SE Houston (Hobby), TX(Zone 9a)

I just bought an old MICROWAVE oven for use in sterilizing my potting mix. Big MW proof bowl (I use glass).

I sprinkle the potting mix with the faucet sprayer in the kitchen sink, with enough runoff water left so the mix doesn't burst into flames in the MW.

Nuke on high, uncovered for 15 minutes. COVER the bowl tightly and the steam will take care of any uglies. Let sit until the mix is cool.

If they don't die after that, they deserve to live...

Liberty Hill, TX(Zone 8a)

GG- Thats exactly what I do. Just didn't want to admit it. I did put Chicken Food in the microwave to kill the weevils and after 7 min. on high they were crawling out of the bowl, I think the feed got too hot, never did kill the weevils tho.

SE Houston (Hobby), TX(Zone 9a)

Try 15 minutes. If they crawl outta that bowl, send 'em to me and I'LL eat em...

Pine Island, FL(Zone 10a)

Eek! I can see where this would be effective, doesn't sound like the most fun I'll ever have. I do have an old microwave, but it's pretty small. Seem to recall my neighbor has a big old mircobeast in his shed he uses for woodworking or something, so I'll hit him up.

Potting mix is primarily peat, perlite and vermiculite, right? Perlite always seems like styrofoam to me, so I hope it doesn't melt! Let's see....40 growboxes, probably splitting into 3 or 4 batches at 15 minutes each.... I'll check back with you around Christmas. :) I wonder what I have that is big enough and will withstand a month in the microwave?

Where should I ship the varmints that crawl out? You folks in Texas will eat just about anything.
Seriously, I appreciate your help. Thank you.

(does this kill fungus, too?)

Liberty Hill, TX(Zone 8a)

That's what I use the microwave for is to kill the fungus. The thing about the chicken food was just a side note. I still can't believe it didn't kill the weevils. I think (hope) gg was kidding about the weevils. I can't believe she would eat them?

Pine Island, FL(Zone 10a)

Hey, I know for a fact my sister-in-law tried to feed me weevils & rice. She's notorious for serving bugs and moldy foods. (she's nice enough, but they always buy 100lb bags of stuff to save a buck and usually throw 2/3 of it away because they rarely cook. Plus she stores stuff in her 150F garage)

Alrighty then. I must cook my dirt thoroughly before serving. Thank you for killing my fungus too!

Crestview, FL

Try buying some huge contractors clear bags and packing all the potting mixes in those and letting the sun solarize them, then put the mixes into 18 gallon totes. You can also treat the medium with serenade, much simplier than a microwave. The serenade takes care of any funguses; don't know about bugs though, spray with beneficial nematoids and hope for the best? Hey, I got 18 - 20 18 gallon totes full of medium can you imagine how long it'd take to microwave all that? Not only that, my old microwave is shot and just bought a new one that I want to last a while, they aren't cheap. I do plan on spraying my entire acre with beneficial nematoids. All you have to do is wet the ground for 3 days running before spraying the nematoids, and then spray the nematoids into the soil using a pumper sprayer. They multiply each year, and they eat over 200 bugs, including beetle larva (grubs), termites, and all other kinds. So, what would be the harm in spraying them in the totes you have medium in????

San Angelo, TX

Joy - Where do you get the beneficial nematoids? Any other info I would need to order the right kind? My local nurseries are not very helpful when asking for anything not lawn related - and not that so much a lot of the time.

Crestview, FL

StillFlyin: There are lots of places to buy them, last time I bought them from Gardener's Supply Co; but had to buy the lady bugs and other bugs from them too, but noticed that Earthbox sells them now, and a lot of organic gardening places do too. They are not that expensive, like around $39 for 1,500,000 of them which covers a lot of ground. I know what you mean about not finding what you want locally sometimes. I wanted to buy about 200 strawberry plants for November planting, the Camarosa's do well here; but are hard to find if you don't get them locally, but, they are not selling plants to the public this year, so might try Gardener's Choice this February instead. Which means I'll be doing both potatoes and strawberries this February and starting my Spring/Summer garden seeds in the coconut coir seed starter kits. Heck, these catalogue places won't even let me place my seed orders til the new catalogues come out and that won't be til December.

Pine Island, FL(Zone 10a)

fyi, I gave up on nuking the potting mix. What a mess.

Crestview, FL

Just put all the potting mix in a clear huge bag, let the sun hit for it about 2 weeks, then dump it into 18 gallon totes; put the lid on and forget about it til Spring/Summer. The sun will solarize it. I have 22 - 18 gallon totes full of potting mix, can you imagine if I had to microwave all that?

Spring City, TN

Coming way late to this, but I pile used potting mix into a compost pile just for that purpose. When I have enough to mess with, I bag it in BLACK trash bags and leave in the sun a month.

Why would clear bags work better? Black should heat up in the direct sun more than clear, shouldn't it???

Everett, WA(Zone 8a)

>> Now I have so many planters and buckets I don't want to keep buying the mix, so if I re-use it, how do I keep the accumulated salts and unused fertilizer from damaging the plants?

If salts and excess fertilizer were the ONLY problems, you might be able to pile all your old mix into a flat-top pile and spray water on it repeatedly, maybe over several days. If enough water runs through the pile, it will flush away anything soluble.

Of course that lets microbes, insects and weed seeds to get into your mix. You might be able to fill large bags standing upright with your old mix, cut holes in the bottoms of the bags, and flush them down from the top, keeping your mix a little cleaner.

Actually, it sounds easier to just pull as many roots as you can out of each bucket, discard crusty soil from the tops, and flush each bucket at least 5 times with clean water - flush it from the top down, draining the salty water out of the reservoir. When done, empty the buckets carefully so that you can also discard mix from the very bottom of the bucket. That will probably have the most salt. Also, since it was the least well oxygenated, it will have m ore undesirable microbes.

But that doesn't address fungus and other unwanted microbes such as soil diseases. Flushing away decomposed organics would give fungus less to eat, which might discourage them a little. But if the fungus was bad for roots, it would be bad for them again when you plant new plants.

Solarizing with heat might work well in FL! Or spreading it more thinly in full sun and hoping for lots of UV.

But if the mix is not in bags, microbes and spores and weed seeds will enter it from the air,

Usually very well-aerated soil encourages beneficial microbes more than harmful ones, but would that work with soilless mix? I don't know. You can get excellent aeration and drainage by adding coarse amendments like pine bark nuggets and chips and coarse shreds (not fines or small shreds). You need enough peat or bark fines to maintain the "upwards" wicking flow. When the mix is coarse enough, you can occasionally water very heavily from the top so that some salts are flushed out the overflow tube.

One good thing about bark: it is cheap enough that you might be willing to demote 1/4 or 1/3 of your mix every year, from buckets in to a raised bed, so none of it gets to be more than 3-4 years old. Use the older mix in buckets for hardy fast-growing plants. Each year start 1/3 or 1/4 of your buckets with new mix, and plant delicate or disease-prone plants in those.

A more aggressive approach is to introduce a huge number of beneficial microbes by mixing 1% or less rapidly cooking compost to your flushed mix. The desirable microbes will compete with undesirable ones.

Perhaps it would be safer to use filtered compost tea ... well-aerated compost tea. Then you will get a maximum of microbes and a minimum of organic particles.

Assuming your compost heap has a healthy population of desirable soil microbes, they MAY consume undesirable fungi faster than the fungus devours your plants. But that's a gamble. You are still adding some organic matter to your "soilless" mix, which will attract more microorganisms. But 1% or less of active compost should not clog up your mix if you have enough coarse stuff.

Trumbull, CT(Zone 7a)

I believe that Black bags will block UV rays just as most sunglasses do and UV rays kill fungus so from that perspective clear is better. It is probably best to flip the bags so that both sides get exposure.
Edit: just noticed that RickCorey already mentioned UV - I agree.

This message was edited May 10, 2013 8:57 PM

Everett, WA(Zone 8a)

You read that WHOLE long post?!?

My hat is off to you, Sir!

Trumbull, CT(Zone 7a)

Actually, I skipped it the first time, then went back and read it quickly, lol!

I grafted some grape vines today, and it came out much better than I
thought it would, I should go start a thread on it.

This message was edited May 10, 2013 9:09 PM

Hanceville, AL(Zone 7a)

Sigourney Beaver, is that your real name? Just interested, because my husband's grandmother was part Indian and her maiden name was Beavers. Don't hear that name very often. I'm sorry to be off the subject, but if I wait, I'll lose train of my thought. Luciee {;^)

Longview, WA(Zone 8b)

Hi Friends,
I just came to this subject, and it's late at night and I can't sleep.
In reading the information from the the Earthbox site, they recommend that you only need to dig out the old fertilizer and mix in some more gypsum before replanting.

I pour fertilizer into a knee high stocking and use it as a strip. That way I just have to discard the old knee high with the fertilizer to start over.
I am getting up to about 25 grow boxes now and can't afford the soil. I do every 2nd year dump the whole thing out and mix some worm castings in the soil.

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