Potting soil is expensive and having to constantly purchase more can be something of an irritation. After all, we gardeners would much rather be spending our hard earned cash on new and exotic plants to add to our garden such as pink banana trees or myrrh or caper bushes. Although that’s my own personal wish list for the moment, I’m sure all the container gardeners and raised-bed owners out there understand my point. We know that digging the soil out of the yard and using it is a bad idea, but we also remain somewhat sticker-shocked by high potting soil prices. But the dirt you used last season can indeed be recycled provided it is disease and bug free. Otherwise, you’re better off dumping rather than reusing the potential disastrous soil.
Store Extra Soil
Healthy used potting soil will need to be stored if it is not being recycled right away. It can be kept in containers that won’t break or large bags until it is needed again. I like to use empty potting soil bags for this purpose because they’re usually thicker than regular garbage bags and there is less chance of making a total mess. Of course, your mileage on that score may vary.
Since I don’t do much winter gardening, the extra dirt usually sits around until I need it in the spring. Then I dump out any soil-filled containers into a large bag as well. Next take the bag and do the hokey-pokey and turn it all about. My reasoning for doing this is that it stands to reason that there might be some lingering nutrients in areas where the plants roots didn’t reach. Or this could be my wishful thinking and unnecessary work. I’ll let you decide but there you go.
The main problem with potting soil after it has been used is that it doesn’t have a lot of nutrients left. This is especially true if it has been used in conjunction with notorious high energy vegetables such as tomatoes (Solanum lycopersicum). Although there are number of plants that don’t seem to suck the soil dry of essential elements, boosting the nutrient levels is still a good idea. I’ve also noticed that used potting soil tends to get particularly dense and that alone could easily lead to root rot in plants. This is why it is necessary to add some goodies to the recycled dirt.
Excellent amendments for used potting soil include perlite, sand, compost, and fertilizer. Perlite lightens up the soil and improves drainage. If the kind you’re using is by Miracle Grow, it may already have fertilizer so err on the side of caution rather than risk crunchy plants. Sand is another option that is excellent for improving drainage but it’s not as lightweight as perlite. While all the gardening articles I have ever read suggest horticultural grade sand, the closest I’ve been able to find is triple-washed playground sand for about $3 a bag. The material in question works good on finicky carnivorous plants so it is probably safe to use on other plants as well. (It hasn’t killed any of mine to date and I use it liberally).
Fertilizer and compost are good for helping improve the overall soil quality. However, if there are forces against you creating your own compost somewhere other than in your refrigerator, you can get premixed stuff at local retailers. I usually buy the cheapest bags available, which run about $3-5. This mix seems to contain dark crumbly soil, wood chips, sand, and the occasional mysterious lump. This will definitely get the job done but there are definitely better (and presumably more expensive) brands out there.
Once you have obtained the amendments you plan on using, you can either add them to the soil filled bag all at once and shake it up, or mix as you go. The latter method tends to be messier but it’s the way to go if you have a lot of plants with specialized needs.
The one caveat to this entire process is that you probably don’t want to use recycled potting soil for starting new plants. Cutworms can occasionally lurk unseen in the dirt and you won’t know they’re hiding out there until your seedlings tragically bite the dust. There is also the potential to mix up common garden weeds in their early stages with the vegetables, herbs, and flowers that you planted. Of course, if you have a sense of humor you might not mind passing out crabgrass to your friends when you thought you were bestowing them with organic tomatoes. Obviously, it’s better to purchase new soil to grow seedlings than to pass out invasive plants.