We grow many pots of annuals every year. At the end of the season we dump the potting soil into a pile behind our wall. I have been told more than once not to reuse potting soil. Is there something I can do or add to the soil to make it useful again?

Thank you in advance.

Charley

I often re-use my container soil by mixing it (50:50 or so) with fresh potting soil, and adding a little slow-release fertilizer. I've never had any problem doing that for outdoor plants, but I wouldn't recommend using it for a plant that's going to be indoors, and definitely not as a seed-starting medium.

I re-use mine too. Sometimes I mix with freshly made up new stuff, sometimes I don't. My plants do fine.

Mine gets tossed into my veggie garden to help loosen up the soil in there. Works great!!

Just put my container mix into my compost piles normally...those containers that I suspect of having disease issues, I just get rid of the soil.

Re-using soil-less mix for seed starting would probably promote damping off, which occurs when fungi in the soil-less mix attack the tender baby stem right AT the soil line. Usually or always fatal.

If you NEVER have damping-off in seedling trays, but want more of a challenge, you COULD try that. But I wouldn't.

As to re-using it for potted plants, I just don't know. But beware of re-using some mix that was "fragile" and broke down or decomposed part way.

That would reduce the drainage and aeration of the mix by making it finer. If air can't get to the roots, you'll wish you had used a coarser mix when the roots rot.

Just one of many lessons that I learned the hard way...

I would think tossing it into the compost bin would allow for re-use, assuming there wasn't a known disease.

robynanne said:I would think tossing it into the compost bin would allow for re-use, assuming there wasn't a known disease.

Absolutely -- but I wouldn't recommend it for seed starting (which Rick was talking about but I don't think was the original question...)

I agree that an active compost heap cures most ills.

I think that everything in a heap gets eaten by something, that gets eaten by something else, most of which then get eaten again.

Yup! Charley was talking about annuals in pots. Are you still following the thread, or have we drifted too far?

pepper23 said:Mine gets tossed into my veggie garden to help loosen up the soil in there. Works great!!

So does my significant other's.
I have dumped enough in one corner of the garden that it is a different color from the rest.

I have "sterilized" my left over soil. For the most part I've had no problems reusing it, even with houseplants. I also will dump it in my compost.

I just replace about half of potting soil in the pots each year and fling the used soil off a shovel into the flower garden beds it is spread out fairly thin, then sprinkle alfalfa pellets around. This year used some of it to fill in spots in the lawn that were not growing decent then reseeded the grass it grew in very well as we had a lot of regular rain.

Just give it some love. Add something to it. Others have suggested mixing it with new potting soil and that's a good idea. I'm one of those organic nuts and so I'll feed it with whatever I have handy. For example, maybe some liquid seaweed, or a little fish emulsion (yum), or liquid molasses, and throw in a few earthworm castings, maybe a few drops of orange oil, just all kinds of good stuff. Of course I was lucky in a way b/c a farm to market store a few miles away was closing and selling everything at 75% off. I really stocked up! But it's all good and I'll use it all eventually. I do tend to be a lazy plant abuser but it's nice to have the good stuff handy.
On the other hand, you could probably just re-use your potting soil without doing anything to it.
And on the other hand, please don't dump it. Waste not want not. (Did I really just say that?)

How I serilize - I pour boiling water over it & let it drain & cool completely. (Usually the next day). I have the container sitting on a bread tray for easy drainage. I try to position it over a place like the driveway or a hard to weedeat area. That way the hot water won't hurt anything or will do double duty & kill some grass.

I always have spots in the yard that need a little more soil.
It always make me feel better knowing it is still fulfilling a needy purpose.
You would think I would get them all filled up but NO there is always more and more especially where tree roots raise up.
The low spots get them 1st.

Welcome to NGA, @Ojenny!

that's a great idea -- we definitely have some spots in the lawn that could use a little extra dirt! (and I have no idea why I've never thought about doing that... )

My potting soil is not the usual (what I throw in the bin for reuse is 50-75% pumice), but I have found it quite useful a second time around for amending soil when I install succulents in the ground. The rock in there helps balance out whatever compost I might also add fresh when I refill the hole (typically about half of the mix going back in is native soil). As a way of enriching our extremely poor soil, that combination has served for a wide variety of succulents, some of whom can be a bit sensitive about drainage. As I have been installing plants piecemeal, the rate of accumulation of potting soil for reuse matches its consumption.

I do not reuse soil from sick or diseased plants, cuttings that have failed to root, or anything that might possibly be contagious. The risk of bugs or whatever seems to be mitigated by the fact that plants in the ground suffer much less from the usual suspects due to the presence of predators which are absent in a patio container garden.

The question of contamination in reused potting soil (related to the contagion of disease in the container garden) does have some connection with the presence of fungus gnats. Where they are present, which is a lot of places, they have the ability to transfer disease from one pot to another just by virtue of their life cycle. You cannot assume that diseases will stay in the same pot they arrived in, given the presence of dedicated chauffeurs.

Fungus gnats can be really annoying when you are trying to start seeds and need to keep the soil moist. The same conditions that foster their reproduction are associated with small, sensitive plants. Control is possible through strategic placement of fly paper or treatment with a systemic like imidacloprid. Our spiders do excellent work. But I would imagine reused potting soil is probably going to carry over a bunch of gnats unless you do Kathy's heat treatment or something similar. I always cook the soil I use for starting seeds (pretty simple microwave protocol) because of the gnats, among other things.