With any hobby or activity, there are always going to be recurring costs; and for most gardeners, one of the biggest ones is potting soil. Whatever brand you like and whatever kind of plant you’re growing, this nutrient-rich stuff is getting more expensive all the time.
If you’ve got large containers or just lots of them, the total you have to pay when checking out from the nursery or garden center can make your head spin!
Worse, once this soil is depleted, most folks just throw it out or rake it into the yard. It’s always felt like money down the drain to me!
But believe it or not, it’s possible to safely reuse and repurpose your old potting soil. It’s a great way to cut down on waste and save money in the long run.
Grab your gloves, and I’ll tell you about seven clever methods for doing so below.
Consider Sterilizing Potting Soil Before Re-Use
One quick thing before we get to the list: you might want to sterilize your potting soil before reusing it. That’s because various plant diseases, blight, fungi, and other harmful stuff can remain in the soil for ages, ready to infect new plants that it comes into contact with.
You’ve got two options for sterilizing soil: The first is to lay out some thick, black plastic and then spread your old soil out in a thin layer on it. As long as you’ve got warm weather and lots of sunny days, giving it about a week in these conditions should do the trick.
Another option is to bake the soil in an oven. Probably not something you want to do in your own kitchen, but if you’re only repurposing a small quantity, it’s doable. Simply spread it out in a thin layer on a baking sheet and then bake it at 250°F (120 °C) for 30 minutes.
This will easily kill off or deactivate any spores and other microbes. Let it cool, and then you’re ready to go.
Add it to Your Compost Pile
The first and, for most of us, best way to reuse old potting soil is simply to mix it in with our existing compost pile.
Doing so will significantly improve the structure and overall nutrition, and also speed up the decomposition of the pile. That’s because your old potting mix has tons of living, beneficial microbes and other organisms already in it, and they will go to work in your compost pile!.
Now, a couple of things you should consider when going this route. For starters, you don’t want to add any potting soil that smells truly rank or rancid.
Nasty smells indicate infection that could possibly spread throughout the pile and hinder growth. Or, worse, give rise to colonies of harmful organisms that can subsequently attack your plants. Not good!
Next, you’ll want to time this properly. The ideal time to add your soil is when you are turning the pile. This is especially critical if your old potting soil is very dry. You don’t want it to dry out your compost pile even partially.
Lastly, mix it in as you would anything else you add to it. It won’t do much good if it’s just sitting there as a solid layer or heap!
Refortify and Reuse It
When your once-vigorous potting soil is no longer giving your plants the pep they need, that doesn’t mean it’s truly gone bad. After all, it’s just dirt! What it means is that the needed nutrients have been all used up.
Considering that the structure of your potting soil is likely still ideal, you can make a great case for simply re-fortifying it with various amendments and nutrients to once again make it great for growing plants.
Just like amending any other type of soil, this approach begins with a soil test. Gather all of your soil and mix it together, then perform your test. See what it’s lacking and what future plants will need, adding what is required before retesting at the required interval.
Once your test and pH balance results show that it is in the right range, it is ready to reuse!
Use as an Ingredient in Seed Starting Mix
This is another one of my favorite techniques for giving old potting mix a new lease on life. You’ll often hear gardeners decry the use of old potting soil as a poor substrate for starting seeds, but that’s only because they use it straight up when it is depleted, as discussed just previously.
The trick here is an easy one: You should start out by sterilizing the soil, then mixing in your old potting soil with sand and perlite or vermiculite in equal parts.
This mixture will provide great drainage for delicate seeds and seedlings, but also the right amount of water retention. You can also add nutrients via amendments as described previously.
The result is a safe, nutritious, and ideal substrate for all kinds of seeds, one that is ready to use in pots, trays, or any other kind of container you prefer.
Save Money and Soil Filling a Large Container
This is something that always drives me crazy. I have several jumbo containers that I grow lilies and palm plants in, and they seem bottomless when I’m filling them with soil.
I swear, I spent $80 just a few months ago topping one off with brand-new soil, and I thought I was going to lose my mind.
Assuming your soil is safe and, hopefully, sterilized, you can “cut” new potting soil costs by filling up a larger container first with your old soil and then putting the new stuff on top of it.
Assuming your plant is properly sized for the container, it will be a long time before the roots reach down that far to the old stuff.
Using this one simple trick, you can cut your cost for potting in a large container by a quarter or even a third.
Fill in Holes in the Lawn
If you love a neat, tidy, and flawless lawn like I do, seeing a ragged hole pop up in it is tantamount to a personal insult.
Maybe it’s your dog or cat digging a hole when doing their business or looking for prey, or maybe it is the digging of some pest like a mole, groundhog, squirrel, or some other critter. Whatever the case, holes are unsightly.
Large holes especially will leave a bald spot for months on end, but they don’t have to: Grab some of your old potting soil and use that to fill in the hole before sprinkling some grass seed and watering it in.
Your potting soil, though depleted, likely still has enough nutrients in it to get your grass growing quickly and your lawn back to looking its best.
Add it as a Layer in Raised Beds
Raised beds are great for maximizing useful space and increasing efficiency in your garden, but they are also huge consumers of soil. Even a couple of modest raised beds will need hundreds of pounds of soil to fill them.
Using a lasagna or layering method with soil and other organic matter is a great way to not only improve the health of the bed overall but also cut down on the amount of money you’ll spend on rich, fertile soil to get them started. As expected, this is another perfect use for your old potting mix.
If you first lay down cardboard, sticks, and other bulky filler, then some loose fill dirt, then your old potting mix immediately before putting on new, rich stuff, your plants will thrive and you can save a bundle.
Level Containers and Landscaping
Last but certainly not least, don’t hesitate to reach for your store of old potting soil anytime you need to top off containers, level landscaping, or perform other utilitarian chores.
Again, even though your old potting mix will be somewhat depleted in terms of resources, it won’t hurt anything going on top merely to improve aesthetics.
In fact, I keep a 5-gallon bucket of this old soil handy for just such an occasion. I also keep the lid on it to keep weed seeds, pests, slugs, and all that stuff out of it. This keeps it safe, unspoiled, and ready to use at a moment’s notice. For routine touch-ups, nothing is better, so don’t throw out your old soil!
Tim is a farm boy with vast experience on homesteads, and with survival and prepping. He lives a self-reliant lifestyle along with his aging mother in a quiet and very conservative little town in Ohio. He teaches folks about security, prepping and self-sufficiency not just through his witty writing, but also in person.
Find out more about Tim and the rest of the crew here.