How to Re-Use Old Potting Soil
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Can you re-use old potting soil from empty planters? The short answer is yes. However, you’ll need to follow a few tips to ensure your new plants are happy and healthy.
If you’re anything like us, things tend to get tossed in the shed at the end of the gardening season. When we went to clean out our shed last weekend we found 2 large grow bags and a half-dozen large pots filled with oil dried out soil.
We needed soil for our planters and some elderberry transplants, so we wanted to make use of this old soil. It seemed a waste to just through it away and spend money on new potting soil.
But, we also knew that we couldn’t just use the soil as is. Old potting soil can contain pathogens that will cause new plants to wilt and die. It can also be lacking in nutrients plants need to be successful. In order to re-use old potting soil, you need to restore and replenish it.
Here are the 3 steps we use to bring old potting soil back to life for new purposes (note, we do not usually use this old potting soil for new seedlings that are especially susceptible to disease):
Step 1: Heat the Soil
The first step if you want to re-use old potting soil is to heat it up. Baking the old soil in the sun helps to kill off harmful pathogens.
Empty your old potting soil into large black plastic garbage bags, picking out any big roots or sticks. Fill them just enough that you can create a 2-3 inch thick “disc” of spread out soil at the bottom of the bag. Tie off the tops of the bags or twist them and tuck them under.
Place the garbage bags with soil in a sunny spot for about a week. You’ll want about 7 days of good warm sun, so if it rains give it a little bit longer. When you reach into the bags to feel the soil it should feel nice and warm.
Step 2: Add Peat Moss
Your dried out old soil might not hold moisture very well. Peat moss is your solution. Add about 1 part peat moss to 3 parts soil. The peat moss will absorb and hold onto the moisture until your plants need it released. It will also help to hold onto nutrients so that they don’t get washed out when the plant is watered or rained on.
Pour the peat moss on your soil and gently fold it in (peat moss can be very light and blow around, so folding it in helps assure you don’t lose too much of it). Keep turning the soil until it is well mixed.
*Perlite or Vermiculite could also be added at this stage to create pockets of air in your soil and better hold on to nutrients.
Step 3: Add Compost
Old soil has likely lost a lot of its beneficial nutrients, so you’ll need to add compost to get them back into the mix. Compost offers a wide variety of nutrients, such as nitrogen, phosphorus, and potassium. It will also help balance the pH of your soil and retain moisture. When you add compost, you’ll notice the richness of your soil just by it’s look and touch!
For potting soil, you’ll want a mixture that is about 20% compost, or one part potting soil to 4 parts potting mix. I find that the best way to distribute compost throughout the soil is to use your hands. Just dig in there and stir your soil up well!
Now you can use your Potting Soil!
That’s it! Now you have rich, well-balanced potting soil that is great for planters and grow bags. It can help to dampen your soil with water before putting it into your pots to ensure a great even moist start for your plants.
I often refill old soil bags with newly upgraded potting soil so that I can keep it on hand for various projects.