About this time every year, the melting snow reveals our last year’s flower pots and planters tucked away alongside the porch, still filled with last year’s soil. No, I wasn’t too lazy or busy to dump them last fall; we’ve found that reusing potting soil is very successful, and saves money that could be spent on plants instead.
Not being one to just make stuff up, I always compare our own gardening experiences with what university researchers are recommending, just for good measure. Advice for reusing potting soil is all over the board, so I’m going to pass along what has worked well for us – experience being the best teacher, as the old saying goes. And I found many references recommending this same method of potting mix re-use.
Mary and I have reused the potting mix in our large outdoor containers for more years than I can remember – an average is probably about 5 to 7 years for the same soil in the same containers. There are a few easy, but important, steps to follow.
How to reuse outdoor potting mix:
- The first time a container is planted, start with top-quality potting mix such as Miracle Gro Potting Mix (NOT Miracle Gro SOIL), or the custom blends sold at locally owned garden centers. There’s a huge difference in potting mixes, and it doesn’t pay to buy the cheap, heavy, poorly drained mixes. Top-quality mixes can be used for years, making them the better deal. Plus, plants like them better.
- In the fall of the year, after killing frost, pull all plants, shake off the roots, remove all leaf debris, leaving no plant trash on or in the soil. If spring finds the old, dead plants still in the pots, just go ahead and clean up all debris in the spring, but fall is best.
- If plants were healthy last summer, the soil is fine to reuse. If the plants were diseased or did poorly, then maybe don’t reuse the soil. In the past decade, we’ve not had any containers whose soil wasn’t successfully reused.
- When spring planting time arrives, remove about one-fourth of the old potting mix, and add new. Mix the new into roughly the top half of the planter, if the planter is large. This keeps the newer soil closer to the plants’ root zone. If the pots are smaller, just mix the new one-fourth in with the older mix.
- Many potting mixes, such as Miracle Gro Potting Mix, are blended with little beads of slow-release fertilizer that provide nutrition. When reusing potting mix, this fertilizer is usually spent. You can recharge the nutrient content by adding Osmocote slow-release fertilizer. The label tells how much to add, depending on the pot’s diameter. Use slightly less, if you’ve blended in new mix that contains fertilizer. Or you can fertilize planters regularly with water soluble fertilizer, which can be done even if you’ve added Osmocote (which the Osmocote label indicates.)
Reusing potting mix not only saves money, but it saves the hassle of emptying all the pots and hauling in more bags of soil next spring.