7 Ways to Reuse Old Potting Soil in the Garden
Don’t throw old potting soil away! It has many uses in the garden, from amending old beds to filling empty containers. You can refresh old mixes with these seven simple tricks from backyard gardener Jerad Bryant.
Contents
Garden soil can quickly grow expensive! Rather than throwing it out, it’s best to keep it in your garden and put it to good use. Potting soil consists of organic materials like fertilizers, bark, and coco coir, all of which can be reused. There’s no need to throw them away because they belong in the environment.
There are three main considerations for reusing old potting soil: fertility, compaction, and pests. In containers, soils leach nutrients readily with each watering. They’ll need amending with fertilizers, organic mulches, or other amendments. Compaction occurs over time as dirt particles settle and push out air pockets. Plant roots need loose and porous soil.
However, pests often overwinter in potting mixes. Pathogens like fungi and bacteria may persist in containers, while pests like beetles and nematodes remain in the dirt. If you have pest issues in the same location of your yard each year, you may want to consider sterilizing or composting the nearby soils before using them again.
There are many other ways to treat, use, and reuse old potting soil. Grab your empty containers and make a pile of the old dirt; we’ll turn it into humus-rich garden soil in no time!
Repurpose and Reuse
Repurposing involves amending and mixing old soils so they are loose, rich, and fertile again. With a few amendments, you can turn old earth into new dirt. I like to keep a few handy amendments on hand so I can repurpose garden soil whenever I need to.
Things like perlite, vermiculite, and pumice are excellent for adding drainage, porosity, and water retention to existing soils. They are loose, with many air pockets that hold air or water for plant roots to access. Other amendments like compost, organic fertilizers, and worm castings are superb for boosting nutrient levels.
You’ll want to amend and stir the mixes in your garden once or twice a year. If you garden for one growing season, amend them two weeks or more before planting in spring. If you garden for spring, summer, and fall, consider amending and stirring again between the summer and fall crops.
Cultivate Easy-Growing Plants
Rather than reusing the old potting soil in a new spot, you can grow hardy plants in your existing containers, raised beds, and planters. Sturdy specimens like cacti, woody shrubs, and rooting ground covers are perfect for planting in these low-nutrient sites. They’ll thrive without much care, offering you gorgeous flowers and textured leaves for little in return.
If the dirt compacted and fell below the surface of the container, consider adding more on top before planting new perennials. This fresh dirt layer is sufficient for quick crops like lettuce, radishes, and arugula. Rather than amending and stirring, simply put fresh compost or soil on top and plant directly into it.
Avoid planting species that require loose dirt to thrive, as they’ll struggle in the compacted site. Peppers, tomatoes, and eggplants should all grow in fresh or amended soil rather than used, nutrient-poor mixes.
Top-Up Raised Beds
Fill your raised beds with the stuff! Rather than putting it in your yard waste bin, reuse old potting soil in your beds. It works well as a mulch or amendment, offering protection for microbes, plant roots, and worms. The critters will appreciate the extra additions; they’ll break them down into smaller pieces that plants can access.
It’s best not to fill your beds with used mixes, as they’ll quickly compact before roots can grow into them. Amend and stir them first before using them to fill your beds. Unamended blends work well as mulch, though they’re not good options for filling.
Perlite may float to the surface of the beds, forming a layer of white, crumbly rocks. Though they’re annoying, they can be helpful! Rather than raking them away, simply add compost on top of them. Add a layer two to three inches thick, and let it decay and fall. The perlite will remain underneath and provide drainage to the site.
Mulch Garden Soils
Raised beds aren’t the only thing you can mulch! Flower beds, borders, and pathways also benefit from used dirt blends. Simply reuse the old potting mix by placing it on top of bare soil throughout your yard. Apply in layers two to three inches thick for the best results.
Where I garden in the Pacific Northwest, I face frequent rains. The excess moisture causes my walkways to grow muddy in spring. Rather than wallowing in mud, I throw used potting mixes all over them! They soak the moisture and make spongy paths for me to walk on without getting muddy.
It’s best to consider the plant species in your yard before adding these blends to existing sites. If they contain diseases or pests, sterilize them first before adding them to flower beds and veggie gardens.
Throw It In the Compost
It’s not difficult to sterilize your dirt! Though some methods claim you should bake or heat it, hot composting is a simple method anyone can do in their backyard. All you need is a healthy compost pile, a pitchfork, and water.
Composting relies on microbes that battle pesky pathogens. The microbes, along with worms and fly larvae, digest and decompose the organic matter in the pile into humus. In hot composting, the heat they generate during decomposition kills weed seeds, insect pests, and diseases.
To hot compost, make a balanced pile with greens and browns. Greens are nitrogen-rich, while browns are rich in carbon. Turn the pile daily and keep it 50% moist so it feels like a wrung-out sponge. Within three weeks or more, the waste will turn into fresh, humus-rich soil for planting.
Sow Seeds
Another way to repurpose the old mixes is to sow seeds in them! Seed starting mixes are an annual purchase, so why not skip the expense and make your own? You’ll want to sterilize them first, as seedlings are extremely sensitive to pests and diseases. They’ll wilt or rot if they sprout in pest-riddled soil.
After sterilization with hot composting, sift the finished compost to isolate small particles. Then, amend the fine compost with loose amendments that lack large chunks. Coco coir is an excellent choice. It’s environmentally friendly to source and easy to use. Fine perlite also works well in adding drainage and porosity.
Sifting and amending create a usable seed-starting mix for your seedlings! Plant seeds in it, water it, and transplant the mature seedlings that grow when they’re ready to move into the yard.
Because compost is natural with critters inside, it’s best to use it for outdoor seed-starting and not indoors. The compost may bring flies, bugs, or worms inside that are pesky to manage. Fresh seed-starting mixes are best for indoor seed-sowing.
Donate It
If any of the previous methods seem too difficult for your garden, the last step is the best one for you. Gift your old potting soil instead of reusing or repurposing it! Rather than humming and hawing over the work, give them to a neighbor, family member, or friend who gardens.
You may also gift it to garden clubs, master gardener organizations, and community gardens. They’ll definitely appreciate the free dirt! Many clubs and garden organizations run plant sales where they pot up shrubs, trees, and perennials for sale. They’ll put the earth to good use.
The final organization to give it to is your local waste disposal company. Many cities have composting programs where they collect food waste and yard scraps. Others have green waste programs that collect wood, plant scraps, and used dirt. Consult your county’s or city’s agencies online to see what programs they offer.
