How to Recycle Potting Soil
Planting containers add beauty to indoor and outdoor spaces, but yearly potting soil replacement expenses add up quickly, depending on the number of outdoor planters. One way to keep your gardening budget low is to recycle last year’s potting soil. Gardening experts sometimes warn against recycling potting soil because there is a risk of transmitting diseases through the soil and because the soil is often depleted of nutrients. You can put these worries aside if you sterilize the soil and replenish nutrients to bring new life into the soil for growing healthy, beautiful plants.
Allow the plants in the outdoor planters to completely die off to remove the live root system and foliage.
Pull the dead plant from the outdoor planter and shake the dead plant over an empty 5-gallon bucket to remove potting soil clinging to the dead root system.
Discard the dead plants in a compost pile or over a garden area to decompose. Another option for recycling the dead plants is to spread the dead plants on a lawn and mulch them with a lawnmower. There’s no need to throw dead plants out with the garbage when they can decompose to contribute to healthy soil.
Scoop the remaining potting soil in the outdoor planter into a wheelbarrow by hand or with a garden trowel. If the planter is small, simply pour the soil into the bucket.
Pick any remaining roots, rocks and debris out of the potting soil by hand. You can also sift the soil through a screen.
Add approximately 2 gallons of peat moss and 1 gallon each of perlite and prepared compost for every 5 gallons of potting soil in the wheelbarrow. The peat and perlite aid in moisture retention and the compost restores nutrients to the potting soil. You may also choose to amend the soil with a slow-release, granular fertilizer or add fertilizer to potted plants according to individual plant needs.
Turn the potting soil in the wheelbarrow with a shovel or trowel to mix the potting soil and amendments.
Transfer the potting soil from the 5-gallon bucket to a large, disposable aluminum baking tray and cover with aluminum foil. Fill the pans within 1 inch of the top of the baking pan so the pan is still easy to handle. Use multiple trays or work in small batches if you have a lot of potting soil to recycle.
Place the aluminum baking tray in an oven preheated to 180 to 200 degrees Fahrenheit. Bake the soil for about 30 minutes to kill any harmful bacteria in the soil. Place a meat thermometer in the pan to ensure the soil doesn’t reach temperatures above 200 degrees F because this could cause plant toxins.
Remove the trays from the oven at the end of the baking cycle and dump the potting soil from the aluminum baking pan into the wheelbarrow; allow it to cool. Repeat the previous steps until all of the soil is baked and cooled.
Test the potting soil pH level with a soil pH self-testing kit. The soil should have an ideal pH level of around 6.8. Add lime to the soil to increase pH levels or iron sulfate to lower pH in soil. Mix in a small amount at a time and retest the potting soil until you get the ideal pH level. You may wish to wait to adjust pH levels for individual plants, because pH needs vary among different plant species.
Scoop the potting soil from the wheelbarrow into large, plastic storage containers with a shovel, then cover with the lid. Store the potting soil in a cool, dry place until you are ready to use it.
How to Recycle Potting Soil. Planting containers add beauty to indoor and outdoor spaces, but yearly potting soil replacement expenses add up quickly, depending on the number of outdoor planters. One way to keep your gardening budget low is to recycle last year’s potting soil. Gardening experts sometimes warn …
Recycle Potting Soil – A Money Saving Option
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.
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Lauren Purcell is a freelance writer from Savannah, Georgia. She is the proud owner of two spoiled little dogs. Her hobbies include gardening (in case you hadn’t noticed), cooking, traveling when she has money, and waiting on her key lime tree to produce fruit.
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Disease and bug free potting soil can be reused. Here's how to revamp and recycle potting soil for future projects!