If you’ve already used potting soil for your plants, you might wonder if you can reuse it. After all, it’s sad for it to go to waste.
Can you reuse potting soil? Generally, as long as the soil is healthy and free of pathogens, you can reuse it for new plants.
But, there are some important things you should know before you go ahead. Read our guide on how to safely reuse potting soil to nourish your plants.
How Long Does Potting Soil Last & Should You Replace It?
The reason why you’ve probably ended up with extra potting soil is that you’ve replaced it. While potting soil doesn’t have to be replaced annually, you will have to ensure the soil always contains fresh, healthy ingredients and that it drains effectively.
Most peat moss-based potting soil mixes on the market will degrade within a year, so they will reach the end of their lifespan within that period.
How can you tell you need to replace your potting soil?
If your soil is too compacted, this is a sign that you should replace your potting soil. When the ingredients in potting soil start to degrade, the particles in the potting soil cling together and become very compacted.
This prevents plant roots from being able to access the oxygen, nutrients, and water they need from the soil in order to survive. So, if you can see that your plants aren’t thriving, it’s best to give them fresh potting soil.
Can You Reuse Potting Soil Instead Of Replacing It?
If you don’t want to throw out the potting soil that you’ve replaced, you can rejuvenate it and reuse it. This essentially breathes new life into it so that it can continue to give your plants the nutrients they need to survive and thrive.
However, there are some important things to bear in mind before you do this.
Risks of Reusing Old Potting Soil
There are some risks involved with reusing potting soil. These include the following:
- Old Potting Soil Lacks Fluffiness: You want potting soil to be light and fluffy to encourage air circulation for your plants. Otherwise, their roots won’t have the space to grow and pull nutrients, oxygen, and water from the soil.
- Old Potting Soil Lacks Nutrients: Another thing to consider with old potting soil is that it will probably lose its nutrients over time. This is also the case with potting soils that contain fertilizers, as they only last for a maximum of six months. By that time, old potting soil won’t have the essential nutrients plants need to grow.
- Old Potting Soil Has The Incorrect pH: You want your potting soil to have the right pH for your plants. Since many potting soils contain peat moss, this can alter the pH of the soil and make it more acidic in nature. Unless your plants crave soil acidity, this can cause them to suffer.
- Old Potting Soil Could Have Been Exposed To Pathogens: Generally, the guideline to follow when reusing potting soil is only to do so if the plants you originally planted in the soil were healthy. If they were diseased, this will degrade the quality of the soil and make it unhealthy for new plants.
How To Amend Potting Soil So You Can Reuse It
There are some things you can do to make potting soil valuable for new plants. Here are the steps to follow when reusing potting soil.
#1 Remove Plant Debris From Old Potting Soil
The first thing you should do if you want to reuse potting soil is to remove plant debris such as roots.
#2 Add Amendments To The Soil
You can’t rely on old potting soil to be healthy enough for plants. So, you will have to add a bit of new potting soil to the plant container along with the old one you’re reusing and consider adding a soil-revitalizing product, too.
This boosts the soil’s ability to be well-aerated, maintain the correct moisture, and replenish its nutrients. An example of a product to use is a slow-release fertilizer or compost.
However, if using compost, do so sparingly. Since compost is quite thick, it can compact the soil. Settle for using a ratio of one part compost to three parts potting soil so that you don’t put too much compost in the soil.
#3 Sterilize the Soil
Sterilizing potting soil helps to remove bacteria, pathogens, and insects in it that could harm the new plants you wish to grow.
There are different soil-sterilization methods you can try, such as the following:
- Steam: You should steam potting soil until it reaches 180 degrees Fahrenheit, or for a minimum of 30 minutes. You can use a pressure cooker to do this. Put a few cups of water in the pressure cooker, then put pans containing four inches of soil over the top of the rack. Cover the pans with foil and close the lid of the pressure cooker. Ensure that its steam valve is left open so that steam can escape. Once the steam has escaped, close the valve and heat it at 10 pounds pressure for up to 30 minutes.
- Heat: Another way to kill pathogens in potting soil is to heat it up in the oven. Put four inches of soil in an oven-safe container, then cover it with foil. Bake it for 30 minutes at 180 degrees Fahrenheit. Avoid baking it at a higher temperature as this can cause toxins to get produced in the potting soil.
How to store sterilized potting soil
Once you’ve sterilized your potting soil, you should ensure you store it correctly. Here’s how:
- Fill a storage bin with a cleaning solution that’s one part bleach to nine parts water, and let it soak for half an hour.
- Remove most of the cleaning solution but leave behind a small amount so that you can clean the interior of the container.
- Remove the cleaning solution so that there’s no excess.
- Leave the container to air dry so that it’s dry before you store potting soil in it.
Although you can sterilize your soil with methods such as the above, there is debate about whether sterilizing potting soil is worth it.
Some sources state that sterilizing the soil not only removes pathogens but also healthy microorganisms, so they advise that it’s best to throw away potting soil if you think it contains pathogens.
So, you might want to throw away old potting soil that contains pathogens or disease-carrying insects, especially if you don’t have the time or inclination to try to sterilize it.
Other Things You Can Do With Old Potting Soil
If you don’t want to reuse potting soil for growing new plants, you can reuse the potting soil in other ways. These include the following.
- Fill up holes in your garden. If you have holes on your property, use old potting soil to fill them up. This is perfect for small indentations in the ground, such as those caused by your dog or squirrels.
- Throw it in the compost pile. You can also put old potting soil in your compost bin. That said, the potting soil should be healthy. If it’s filled with weeds or pathogens, you shouldn’t put it in your compost. These can both survive in the soil and get put back into your garden in the future, where they can disrupt the healthy growth of plants.
What does potting soil contain?
Most potting soil mixes on the market contain ingredients such as peat moss, perlite, and bark. These help to encourage soil aeration and drainage so that the soil doesn’t become too compact.
Can you mix potting soil with garden soil?
Although you can mix potting soil and garden soil if you’re filling raised beds, it’s not ideal for container plants. This is because garden soil lacks the ingredients found in potting soil that benefits plants, such as minerals and organic materials.
If you have old potting soil, you might wonder if you should reuse it or throw it away. In this guide, we’ve looked at everything you need to know before reusing potting soil, and how to rejuvenate it for use with new plants you want to grow.
While you can reuse potting soil if it’s in healthy condition, you will have to amend it before use.