Calling all green thumbs: When dumping out last season’s container plants, the old soil doesn’t have to go into the trash. In fact, it’s better for the environment (and your wallet) if you find new and innovative ways to repurpose used soil. “The good news is most old soil isn’t ‘bad,’ it’s just tired,” gardening expert Donna Letier explains. There is one asterisk to this: If the soil has been used with diseased or pest-infected plants, it’s best to discard the soil or use it in non-edible contexts (more on that later).
But if the soil didn’t come from a sickly plant? You’re good to go. Here’s our gardening experts’ top tips for repurposing old potting soil.
Donna Letier, CEO and co-founder of Gardenuity
Kim Zimmerman, master gardener and owner of floral studio Rowdy Poppy
The Lifespan of Potting Soil
Kim Zimmerman, owner of floral studio Rowdy Poppy, says this is tough to tell just by observing the soil itself—although there are a few clues to keep your eyes peeled for. If the soil smells moldy, has visible fungus, or the texture is overly compacted, then it’s likely lost its vivacity. “For indoor plants, the soil is good for about a year; for outdoor pots, we give them 1-2 seasons, depending on the size of the pot,” Zimmerman explains. “The larger the pot, the longer I’ll allow that soil to be used.”
For pots you can easily lift yourself, Zimmerman recommends replacing the soil completely every year. (“We will still amend the soil each season even if we aren’t doing a total refresh,” she says.) If the pot is particularly large or you can’t lift it safely, removing and replacing half the soil every few seasons should be sufficient. However, if the plant is diseased, the soil should typically be discarded ASAP.
The Benefits of Soil Reuse
Both of our experts advocate for reusing potting soil because it’s a sustainable practice that cuts down on unnecessary waste. Instead of throwing soil in the trash where it can take up space in landfills and release greenhouse gases, you can refresh and reuse it in simple ways.
Letier says it’s also a good reminder for new gardeners that you don’t need to be perfect to grow healthy plants; just thoughtful and willing to care for what you already have.
What to Do With Old Potting Soil
Letier and Zimmerman share their favorite ways to reuse potting soil below.
Bring It Back to Life
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If you want to revitalize your old potting soil mix, consider combining in compost, nutrients, and a bit of fresh potting mix. Some gardeners also create a “soil recycling bin” at home, where they combine old soil from different pots and refresh it all at once.
Letier recommends a simple DIY method to make a homemade “banana soup” to re-enrich your soil. She says the mixture adds key nutrients to the soil (like potassium, phosphorus, and calcium from the banana and eggshells), which is great for plant roots and flowers.
Materials:
Two bananasWaterStoveLarge potThree eggsGround cinnamon (to help fight mold and fungus)
Instructions:
Boil two banana peels in about 3–4 cups of water for 10 minutes. Blend the banana water with 2–3 crushed eggshells.Add 2 tablespoons of ground cinnamon to the mixture. Allow the mixture to cool.Pour over your old soil, stirring occasionally for 24 hours.
Use It in Compost
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If you have a compost pile or want to start one, old soil may be your new best friend. Letier suggests using it as a base for compost since it’s already full of natural materials and helpful microbes.
Mix it with kitchen scraps and carbon-rich items to create a healthy environment that’ll help break everything down faster into usable compost. The soil will also help soak up extra moisture from food scraps thrown into the pile.
Fill in Divots
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“Got any divots or low spots in your lawn?” Zimmerman asks. “Sprinkle in layers of old soil and allow the grass to fill in over them.” It’ll be an easy and inexpensive visual upgrade.
Add It to a Hardy Plant
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Old potting soil can still be useful for growing hardy plants that don’t need rich, nutrient-packed soil, Letier says. Succulents and cacti, for example, do well in reused soil if you mix in sand or perlite to improve drainage. Native plants and tough perennials like daylilies, black-eyed Susans, and hostas are also great choices. (They’re typically more resilient and can thrive in less-than-perfect conditions.)
Donate It
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Ekaterina Vasileva-Bagler / Getty Images
Consider donating old soil to local schools or camps. “Kids can use the dried soil to make dirty paint or textural nature art,” Letier explains. You can also consider sharing the soil with neighbors, a local community garden, or “buy nothing” groups on social media.
Use as a Top Dressing for Garden Beds
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Zimmerman recommends using old potting soil as a top dressing for garden beds before you add mulch. Spreading a thin layer over the surface helps improve water retention and soil structure (also known as tilth).
Cheers to boosting your garden’s health while also cutting down on unneeded waste.
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