I have a container garden and the most common problem every year is what should I do with the potting soil from the previous year. Should I throw it away or is there a way to reuse it?

You should not throw away old potting soil because you can reuse it for growing new plants. You just need to improve the texture and nutrients in the potting soil before reuse. The only reason to throw away old potting soil is if it contains pests or diseases from growing previous plants.

I’ll help you understand the benefits of reusing old potting soil. I’ll also show you the method of improving the potting soil and making it ready for growing new plants.

How to reuse old potting soil

As long as the potting soil is free from pests and diseases, you can make use of it to some benefit in your garden.

  • The most common use is to mix in the old potting soil with a new one and reuse it for growing new plants in your garden.
  • You can also add the old potting soil to your outdoor garden or lawn and get the benefits of improving texture.
  • You could use the old potting soil to cover up any holes in your garden that may have been dug by animals such as dogs, moles, or rabbits.
  • You can add the old potting soil to your compost pile if you are making your own compost. Or give it to your community garden if they have a compost pile.
  • If you have a large container for growing plants, you can use the old potting soil as filler material at the bottom. This will help you save money on the quantity of potting soil you need to use in the large pot.

Problems with old potting soil

The main problem with old potting soil is that it may contain pests and diseases from the previous plant growing in it. These pests and diseases can harm any new plants that you try to grow in this potting soil.

There may be weed seeds that have been deposited in the potting soil due to wind, birds, or animals. If you try to reuse this potting soil, there’s a chance that these weed seeds will sprout.

The other problem with old potting soil is the nutrients and minerals may have been exhausted as the plant has absorbed them.

The nutrients and minerals may also have been leached out of the potting soil after frequent watering.

If you used tap water or hard water to water the potting soil, there is a chance that a lot of salt is deposited in the potting soil.

You can observe this in the form of a white residue on the surface of the potting soil. This salt deposit can be harmful if you try to grow a plant by reusing this potting soil.

How to recycle old potting soil

don’t recommend you try to reuse potting soil if it contains pests or diseases. It’s best to dispose of the soil and avoid risking the health of your new plants.

If the potting soil is free from such problems, you can reuse it for growing new plants. You just need to ensure the soil is healthy and contains the required nutrients.

  • Once your existing plants have died, you can take them out of the pot. Spread the potting soil on a tarp. Shake the roots of the dead plants on the tarp so any attached soil falls on it.
  • Then let the potting soil stay on the tarp for a few days so the moisture can dry out. Remove any unwanted roots, stems, leaves, or debris you find in the potting soil.
  • Once the potting soil has dried out, you can break any clumps that have formed due to the compaction of the soil. Make sure the texture is crumbly and falls apart.
  • You need to sterilize the potting soil which will ensure no potential pests or diseases are remaining in it. The easiest way to do this is to put the potting soil in black plastic bags and leave it in the hot sun for four to six weeks.
  • But I prefer to rather use an oven to heat the soil. This is a faster and more effective process to eliminate any unwanted pests and diseases from the potting soil.
  • You can place the potting soil in aluminum foil on a baking tray. Preheat the oven to 180-200 degrees and place the baking tray in it for 30 minutes.
  • If you have a large amount of potting soil, you may need to do this process in batches so all of it can be sterilized.
  • Once the potting soil is sterilized and cooled off, you need to introduce the required texture and nutrients to it.
  • It’s best to mix this old potting soil with new potting soil in a 50:50 ratio. You can spread the potting soil on a tarp, add the new potting soil, and then mix it in with a trowel or your hands.
  • Now that the soil texture is done, you need to add some nutrients to the potting soil. You can do this by adding a slow-release fertilizer to the potting soil. Or mix in some organic compost that will add nutrients as well as beneficial organisms.
  • You can check the manufacturer’s instructions on the quantity of slow-release fertilizer you should add to the potting soil. If you’re adding compost, you can use 25 percent of the amount of potting soil. Mix in the fertilizer or compost well with the soil.
  • Before you can use the potting soil, it’s good if you can test it with a soil testing kit. This will show you the pH level of the soil. For most plants, you want the pH level to be between 6.5 to 6.8.
  • If the pH level is lower than this, you can add lime to increase it. If the pH level is higher, you can add iron sulfate to lower the pH. Mix a little bit of the material at a time and retest to check if the pH has been corrected.
  • Now your potting soil is ready for reuse. If you’re not going to use it immediately, you can store it in a plastic bag. Seal it well and store it in a cool, dry place. The potting soil can stay in storage for 6 months without any problems.