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May 2, 2009 09:13 PM

Reuse of soil in containers

I grow a container garden, and wonder if I can reuse potting soil, either partially or completely for my veg this year. I usually feed with bone meal and fish emulssion every couple weeks. I don't have compost. Could I use half new / half old? What if I boost it up with some coffee grounds or egg shells? Looking to save a few bucks. Hopefully I'll soon figure out a compact way to compost, but until then I would love some feedback. TIA

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  1. I think container soil gets very depleted but I have removed 1/2 the soil from a large container, mixed in some Cock-A-Doodle Doo fertilzer. Then, topped with new potting soil mix. This is for annual flowers. For veggies I use new soil or one made from a mix such as Mel's Mix used for square foot gardening. Last year we had a good size vegetable garden for the first time in years (moved to a house with plenty of sun) using the lasagna method which is basically building a compost pile and planting in it. This method is suitable for containers but I haven't tried it yet in containers. For compact composting, you might consider worm composting. Mine live in a large Rubbermaid tote in the basement. They quickly turn kitchen waste and shredded paper into very rich compost.

    1 Reply
    1. re: dfrostnh

      Thanks for the advice. I keep thinking about the worms, but that's the kind of project I start and my SO has to finish. He's not so keen on the idea so I haven't started it yet. I'm inspired to look more into the lasagna method. I started about twice as many seeds this year and don't really want to spend all that money on potting soil.

    2. I reuse my soil every year. I mix the old stuff with some chicken manure and then plant. Never had a problem reusing the old.

      7 Replies
        1. re: corneygirl

          I do grow vegetables in the reused soil. As far as I know it hasn't hurt them any!

        2. re: mels

          Me too. I grow all my tomatoes & peppers in containers. At the end of the season I dump out all the soil in a big pile and in the spring mix in half dozen big bags of new soil.

          1. re: mels

            Also a dumper and re-mixer. To bolster container soil, I mix in Coast of Maine-TM compost with lobster shells plus some peat or like product to lighten it up. Every so often -- maybe five years or so -- I dump everything and start anew.

            1. re: harrie

              ok, all re-users - what proportion old soil to your additions? If using chicken manure, how old is the manure? During the growing season, how often do you fertilize and what do you use?

              1. re: dfrostnh

                You can buy bags of composted chicken manure. Do not use fresh. Chicken manure is very high in nitrogen-- you can easliy burn or overstimulate your plants with chicken manure. Too much nitrogen can be as bad as not enough. Root crops will not form roots, blooming plants will go to excessive growth, and drop blossoms,. etc.

                Most veggies need more Phosphorus than Nitrogen. Phosphorus is responsible for helping a plant produce blossoms (fruits) and roots. A good Nitrogen-Phosphorus-Potassium ratio
                (aka the "N-P-K" value listed on packaged fertilizers) for veggies is 5-10-10. Organic sources are best, as they will help with fostering soil microbe activity, which leads to healthier plants better able to withstand difficult conditions. They take time to be broken down by soil microbes to forms a plant can use, so are nature's Time-Release fertilizers. They also contribute humic acids, essential to healthy soils.

                For anyone wanting a good tutorial on soils and fertilizers, Rodale Books has some very good ones. The venerable Encyclopedia of Organic Gardening is a good one you can usually pick up at a used book store.

                On recylcing soils, I think it's more important to pay attention to the structure of your recyled soil, rather than focusing primarily on the nutrient content. Sure manures add food value, but soil structure (the texture you feel when you squeeze it--the tiny bits of composted organic materials) is most important when it comes to holding moisture, creating oxygen holding capacity (roots die when they have no oxygen, like when you over-water) and ability to keep roots cooler when grown in containers (especially plastic which can overheat).

                I'd say at least 50% virgin soil mix or compost should be added to recycled potting soils.

                Also, watch out for overwintering soil-dwelling insects and their eggs.

                It would be better to hot-compost your used soil than to bag it or store it out in the open for later use. Good sanitation is extremely important.

                1. re: dfrostnh

                  I probably go with more like a 25% new - 75% old mix, soil-wise; but I also throw in a huge amount of the aforementioned CoM compost and peat, so that would bulk up the new material, maybe close enough to 50%.

                  I fertilize with fish emulsion -- which stinks to high heaven, even diluted in water, but works wonders and is usually considered organic; plus the stink sometimes helps keep critters at bay -- about every three weeks, maybe, depending on rainfall. With container gardening, nutrients can flush out of the container if you have a heavy rainfall, so it's not a bad idea to fertilize a little lightly (unless something really needs help) but more frequently.

                  toodie jane brings up an excellent point about bad insects and/or their eggs in the soil. If I have a bad year with a container and deduce the problem is something in the soil, out it goes (down a big hill, in our case) ASAP. Mixing it in with the other (good) container soils for the winter won't fix the problem, but will just spread it around. And if your containers are close together (like mine - I have a tiny patio), bad critters can migrate.

            2. sure you can reuse it. It is fluffy and organic and you can add new components (compost, etc) to revive it.

              1. Depends on the mix. If it has a lot of peat moss, toss it. If it's based mostly on fine pine bark you can probably get away with mixing half and half (at least I have, so far). Try to plant unrelated plants each year to reduce the risk of soil borne diseases.

                7 Replies
                1. re: Zeldog

                  How can I tell what was in the mix? I know very little about gardening (pretty much all of it is in the OP).

                  1. re: corneygirl

                    Like I said, if it has not completely broken down and turned to dust, you can reuse, by mixing with new organic matter, like compost, maybe add some vermiculite or perlite. In containers, most of the nutrients are going to come from fertilizer you add. The container potting medium needs to be light (so the container is not too heavy) and it is there mostly to provide an anchor to the plants, It needs to hold moisture to the right degree and also to allow some air into the soil. It should feel light and moist, not soggy or dried out and dusty. You will be feeding and topdressing the plants through the season to give them the nutrients they will need, this will mostly not come from the potting medium (though you can put in slow release fertilizer)

                    make sure that you are using the right sort of fertilizer for what you are growing - and that if you are growing herbs they do not need so much.

                    1. re: jen kalb

                      just a note on vermiculite, which is often added to commercial potting soils to add water-retention capabilities. (it's the sort of soft, sparkly material--looks sort of like a flaked mineral product, which it is)

                      Vermiculite is a mined mineral, and because it occurs in soils in close proximity to ASBESTOS veins, it has been taken off the market in some states.

                      You can instead add polymer crystals or other natural products to your soil mix to help hold onto water in your potting soil.They absorb water and expand to many times their dry volume, then release the water to root tips as needed. These are sold in garden centerse in the lawn and garden dept, near wither the small bags of soil, or the fertilizers.

                      Only very small amounts of these water-retention agents are needed. (a teaspoon or two in a 5 gallon pot.)

                      1. re: toodie jane

                        Ive used the crystals in window boxes and they are excellent - just dont overdo.

                        1. re: jen kalb

                          Thanks to you both for that tip, it kind of defeats the point of growing your own, if there is asbestos. Is this the white balls? Also, will it say on the label.

                          1. re: corneygirl

                            I think the white balls you are thinking of are perlite, which is a totally different mineral but retains water much like vermiculite.

                            As for asbestos in vermiculite, what does "taken off the market in some states" mean? I don't believe it means some states have banned the sale of vermiculite, as almost every commercial potting or seed starting mix contains vermiculite. It has been an issue, however. See the link:


                            And polymer crystals may be great stuff, but they are no more "natural products" than commercial fertilizers or Hostess Twinkies.

                            1. re: corneygirl

                              the statement that there is asbestos in vermiculite is much too strong.the point is, that you can buy potting soil or compound/amend your own. vermiculite is very useful for lightening and aerating otting soil.

                  2. I grow tomatos and peppers in pots and re-use the soil every year. Each spring I dump the pots to brak up the soil, add bagged organic humus/manure ($1.50 a bag at HD) and more soil/potting mix if needed. I also scrub the inside of the pots well with a light bleach water.