Can You Compost Old Used Up Potting Soil

Composting old, used-up potting soil can be a sustainable way to recycle and repurpose this resource while contributing to a healthier garden. As with any composting endeavor, it’s essential to follow some guidelines to ensure a successful and safe process.

One of the first considerations when composting old potting soil is to inspect its condition. Ensure that it’s free of contaminants, disease, or persistent pests. If you’ve used the soil for healthy, disease-free plants, it’s generally safe to incorporate into your compost pile. However, if you suspect any issues, it’s best to err on the side of caution and dispose of it separately to avoid potential problems in your compost.

Old potting soil can often become compacted and form clumps. Before composting, break up these clumps to improve aeration in your compost pile. Adequate aeration is vital for the decomposition process, allowing beneficial microorganisms to thrive.

Used potting soil is considered a carbon-rich, or “brown” material in the composting world. For proper decomposition, balance it with nitrogen-rich, or “green” materials, such as kitchen scraps, grass clippings, or other organic waste. Maintaining this carbon-to-nitrogen balance is crucial for successful composting.

Old potting soil can be quite dry, so before adding it to your compost pile, make sure to moisten it adequately. Aim for a moisture level similar to a wrung-out sponge. This moisture helps create the right environment for decomposition to occur.

Layering the used potting soil with other compost materials in your pile ensures a balanced mix. By combining different materials, you create a more diverse and nutrient-rich compost.

Regularly turning or aerating your compost pile promotes even decomposition and prevents compaction. This aeration allows oxygen to reach the microorganisms responsible for breaking down the materials, speeding up the process.

It’s important to be patient when composting old potting soil, as the decomposition time can vary depending on the soil’s condition and the composting environment. Over time, it will break down and become a valuable addition to your compost, contributing to healthier and more fertile garden soil.

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Can You Compost Old Used Up Potting Soil
Old soil is also perfect for use as a growing medium

Used soil – ripe for the trash?

Pests and diseases nest in old soil, which then attack the new plants the following year. Wrong! This sentence can be read and heard again and again, but at this point we must urgently clear up clichés and prejudices against old soil. If it – no matter whether in the tub or in the garden – is “healthy” at the end of the season, it would be the purest waste to simply throw it away, because you can do some great things with it. Even soil that is already very old and completely exhausted can still be used further.

Old potting soil

If we clean up our balcony (or terrace, garden or everything), we sometimes have some soil left over in the sack that hasn’t even been used yet, in addition to the soil in the tubs and beds. If it was reasonably well protected from wind and weather, you don’t have to worry about it and can just keep using it next year. It’s best to store it covered in a sheltered place, such as a shed, under a bench, or some other suitable place.

If it has been exposed to the weather and is therefore already quite depleted, you can compost it if necessary (a worm bin or bokashi can also be used for this purpose). And if you can neither compost nor have a garden, you can spread it as a mulch layer on a green strip or the bed in the front garden with a clear conscience. The grasses and plants there will thank you very much. If you have a garden or even a greenhouse, you can of course also use the old soil generously for mulching or use it to loosen up the empty beds in the greenhouse. You can also use it to pimp out and insulate winter quarters for our little garden inhabitants, such as hedgehogs, for extra camouflage.

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Old tub soil

It’s pretty much the same with the soil from the tubs. If it’s already very old and silted up (i.e., extremely fine-crumbly and dry – though it takes a few years to reach this state), you can compost it or use it for mulching. For plants that are sensitive to cold (we’ve heard the fig is one such candidate), you can use it to make a mound around the trunk to provide cold protection. Otherwise, the easiest way is to collect the soil from the tubs in a large container and store it protected and covered during the winter. If the containers are frost-proof plastic pots, the soil can also be covered and stored in them over the winter. By the way, you don’t necessarily have to remove old plant and root remains, just see how coarse they are and decide as you like.

In spring you should then check whether a few winter guests have crept in. If everything looks fine, you can use the soil again. However, you should refresh it with a little compost or new soil; just mix two parts of old soil with one part of new soil or compost – done! Humus from worm bin or bokashi is also a great option. If you want to grow vegetable plants, it is also recommended to add a small portion of horn shavings or other organic slow-release fertilizer to ensure the supply of nitrogen.

The soil in the garden bed

The beds in the garden are also thinning out now. Here you don’t even have to do that much; if necessary, simply remove the old, very coarse plant remains and thoroughly loosen the soil once. If the soil is very heavy, dense and overgrown, it is a good idea to dig it well with a spade to a depth of about 20 to 30 cm to ensure good aeration. Depending on the soil conditions, you can add a little organic slow-release fertilizer (our Bloomify fertilizer would do a great job) or compost to the top layer. This is also a good idea if heavy growers were previously planted. All chemical fertilizers should be off limits!

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If you want to give your soil and the tireless microorganisms some luxury, you can still cover it with a thin layer of leaves or straw. Bark mulch, however, is not so well suited for this purpose, as it can remove nitrogen from the soil. This approach has several advantages at once: on the one hand it avoids too much drying out, on the other hand it avoids too much leaching of nutrients, and in addition it keeps the soil life nice and active. Bonus: This layer also provides a good winter shelter for many small animals and insects!


  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

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