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Reusing Last Year’s Potting Soil

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By David Wall, Mount Pleasant Master Gardener

Many grow vegetables in 5-25 gallon pots using potting mix, soil mix or compost. At the end of the growing season, a question of whether the soil can be reused the following growing season. Answers range from no to yes, BUT.

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potting soil (Photo Credit: simpleandgrand.com/)

First off, at end of growing season, get every growing plant or critter out of the pot. You don’t want anything sucking up remaining nutrients.

If using potting mix, reuse the following year is a firm NO. The nutrients in the mix have largely been utilized, meaning there aren’t enough nutrients left to sustain life next year, even if you’re just growing flowers. Next spring, swap out 50% of the old, replacing it with new mix. Then, new plants can get the nutrients they need, particularly if you add some slow-release fertilizer
and/or other organic nutrient materials, but mix well. If, however, you grew tomatoes, throw the entire mixture away to avoid the possibility of spreading blight to next year’s crop.

Reusing potting soil is slightly different. As with potting mix, the soil will be hardened, thus, making next year’s vegetable plant roots have great difficulty penetrating it. The same is true for water which tends to pool of the surface or run down between the soil and the pot wall. Generally speaking, potting soil will have more nutrients than potting mix, but the odds of having enough nutrients to last the entire growing season is questionable. Mixing new with old, the same as with potting mix, is recommended.

Pure compost should contain more than enough nutrients for a second growing season, but stir the mixture to break up hardened clods. I’ve never gone beyond two growing seasons, soil I have no information beyond two seasons.

In the summer heat, paint dark pots white to help keep temperatures cooler.

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Author: Faith Huffman

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