The potting soil in question is in medium to large sized pots that had/have tomatoes or small fruit trees in them.

5 Answers 5


The only two problems I can think of would be disease and nutrients. There are some diseases (eg. fungi and nematodes) which will linger in soil, so you really need to treat the soil or discard it to somewhere where the disease is not a problem (ie. a different kind of plant).

As for nutrients, these could be topped up with liquid feed or top dressing. I find potting compost settles / compacts quite a bit so there's usually space for top dressing each year. I also re-use potting compost by putting it on raised beds or filling small hollows in the lawn. It isn't the best medium for the latter, but every little bit helps.


It all depends on what was initially potted inside of the soil, to add onto @winwaed you can actually boil some water and pour it into the soil to kill any bacteria or disease. The other thing you can do is use some fungicide to get rid of anything harmful.

Although top soil is fairly inexpensive its a major profit margin for these garden retailers like home depot, lowes, randazzo's, etc. They want people to toss the stuff out and buy new soil each and every year. To me this is a total waste of money and another way to make a dollar off of you. To you a bag of decent top soil is a mere 3-4 bucks...but multiply that by thousands of people buying that stuff and this could be just for one store!

You can always mix it up with some new soil if you still insist on buying new top soil.

  • Hey, this is my big fallback! But in this instance, do not reuse potting soil. I throw old potting soil in my compost if I haven't seen any disease, but I would never reuse potting soil. All it takes is one spore, one virus, one bacteria that are damaging. Getting potting soil with beneficial bacteria and mycorrhizae are critical to plants. Never use chemicals to 'improve' a soil. If you have plants in pots, the best, most educated and in the long run, cheapest thing you can do is get sterilized potting soil.
    – stormy
    Jul 2, 2014 at 22:29

I've read (I think in Rodale's Organic Encyclopedia) that you don't want to till potting soil into your garden, but certainly can use it to help your compost pile.

You can make your own potting soil (even using dirt in the microwave). Which is a good way to save money.

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    Why not? I understand that there might be better choices, but if you've got it, then it seems a good way of boosting organic content and a good way to break up a heavy clay soil?
    – winwaed
    Jun 10, 2011 at 1:23
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    @winwaed, the reason was due to adding molds or junk that might be tempted to grow in your potting soil. I have a tendency to think this has more to do with seed starting soil than potting soil (stuff rich in phosphorous that grows anything). Jun 10, 2011 at 2:31
  • makes sense - it comes down to my comment about disease. luckily it isn't a problem that I've had.
    – winwaed
    Jun 10, 2011 at 2:35
  • I've got one word...STINKY!! Potting soil sterilized with added bacteria and mycorrhizae is INEXPENSIVE. Old potting soil is great and no big deal in plant beds in your garden. Don't use old tomato soil to grow more tomatoes. But this stuff has few weed seeds, not much pesticide residue and ornamental beds as well as lawns will love this stuff. Tilling is only for a first time bed! Just dump on top and smooth out a bit!! Definitely don't throw it away but never again use it in pots...phosphorous is becoming a problem in our soils, too much, FYI. No potting soil with fertilizer please..
    – stormy
    Aug 31, 2015 at 20:59
  • Crop rotation My grandparents had а large garden beside the vineyard; had cared about it numerous years. Every spring they reshaped the garden - putting the tomatoes, cucumbers, pumpkins, carrots, onion, cabbage and other goodies in new places. They told me this is because every plant uses some assortiment of nutrients in the soil. Planting the same kind of plant in the same spot for several concessive years would exhaust the soil, they explained. Later, at the university, the teacher in Engineering Ecology told us planting the same crops in the same place is one of the biggest problems of contemporary agriculture.

  • Adding compost I have read that compost not only supplies the soil with nutrients, but also aids texture. This summer is my second year of balcony gardening. I use the same soil as wast year, mixed 3:1 with compost. I compost* most of what I harvest. Everything is growing fast & healthy for now, so let's hope this works out forever :D I would really love to be closer to sustainable.

* - no that was quite wrong! Proper composting takes either having a big pile (>1m^3) and waiting for an year or waiting for 3 years. Else all of the known and unknown pathogens persevere!


Plants in pots need every ounce of care we are able to provide. Potting soil is pre-mixed and sterilized. Disease is a deal breaker. Clean, fresh soil and a little bit bigger pot once a year is the best insurance I can imagine versus losing my plants(s) slowly but surely to death. In-door plants are long-term perishables. Some longer than others...we can give our plants an 'edge'...it isn't a big deal to make your own soil. I've done it. I've decided that it was much more cost effective to use a ready-made product. Sterilize your own and let me know how that works out!

Potting soil now comes infused with important bacteria and mycorrhizae to incorporate life back into the sterilized soil. Lots of decomposed (and non-decomposed) organic matter fluff up the mineral content.

During the seasons, the organisms in the soil eat up the organic matter that once fluffed up the potting soil. Top dressing with decomposed organic mulch every month or so would prevent the compaction that occurs as organic mulch is used up within the soil. Otherwise your plants are trying to survive in depleted, brick-textured soil. To top dress too late or to use non-decomposed organic matter might take longer than the plant can live to be useful to the plant.

I put my indoor plants outside during the summer on a protected porch. Seems to rejuvenate my plants tremendously. I also include new potting soil, no rocks 'for drainage', never add garden soil, put tiles beneath the pots to increase drainage. I enjoy getting a new pot or two every year and my plants always look greenhouse-new. Also, I use extended release fertilizer, sparingly and when I water everybody goes into the shower, gets drenched in cold water, drip dries then back out into their normal spot. They don't get water until each is as dry as the plant can get without undo stress. Any sign of insects or disease I've got my handy-dandy loop and microscope to KNOW who my plants guest are...great tools!!

Potted plants are prisoners OF their pot-world. Using depleted or disease tainted soil is just a big NO-NO and a needless risk that doesn't pay for itself. Hope this helps!

  • 'In-door plants are long-term perishables. Some longer than others.' I disagree. I have a nice collection of house plants, and haven't added any new ones for years. They will multiply, not decrease in value, if you give them the right care.
    – J. Musser
    Jul 3, 2014 at 1:36
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    Oh gees. IF one knows how to care for indoor plants, they should last a long time. Otherwise, what plant would chose to live indoors? You know plants! Of course your plants will live a long time. My point is growing plants indoors where it is dry, dusty and dark is not natural...takes a bit more work and vigilance. If I were a houseplant I'd sure hope it was J. Musser who'd take me home!! Grin!
    – stormy
    Jul 3, 2014 at 2:38
  • I use old potting soil all the time. It just needs sterilizing and re-fertilizing.
    – J. Musser
    Jul 3, 2014 at 4:15
  • Of course it's you! Grin, so you cook your soil in the house? (Pouring boiling water over soil does not sterilize. I'd only trust water coming from unknown sources boiled for 10 minutes)...I've made my own soil as well, a long time ago. PEEEYEEW. But sure like it when I can blame the soil maker instead of me if something goes wrong, ha ha.f I am not serious. Spend my time making my own garden soil better and right now that is a lot of work. And...I've gotten lazy!
    – stormy
    Jul 4, 2014 at 2:41

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