What to Do with Old Potting Soil? (How to Reuse It, FAQs)

potting-with-rosy-soil

Wondering what to do with old potting soil?

Adding old soil to your veggie patches or flowerbeds is one way to use it. But if you don’t want to add it to plants directly, you can compost it instead. 

That said, old potting mixes can have low nutrition, excess salt, and various other issues you need to address before reusing them.

In this article, we’ll unravel what you can do with old potting soil and how to reduce the risks involved. We’ll then answer two relevant FAQs and highlight a sustainable alternative to conventional potting soil.

  Further reading

  • Refresh your money tree with this well-draining and fertile Money Tree Soil.
  • Also, you'll want to switch to this Ideal ZZ Plant Soil when you read the benefits it brings for your ornamental plant.

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What to do with Old Potting Soil?

Old potting soil may lack the nutritional value for potted and container plants. But that doesn’t mean you should throw it away. 

Here are three ways to use old potting soil:

1. Reuse the Soil in Your Garden

If your old mix contains perlite and vermiculite, you can use it to enhance soil structure and drainage in vegetable containers, flower beds, or garden plots.  

You can add the old soil atop existing soil surfaces (as a top dressing). Alternatively, you can use it to make borders, fill holes, or increase the volume of raised garden beds.

However, keep in mind that traditional potting mix ingredients like peat moss, vermiculite, perlite, and treated pine bark are bad for the environment. 

Why?
Sourcing vermiculite and perlite requires energy-intensive mining — a significant contributor to rising greenhouse gas levels. On the other hand, pine bark depletes soil nitrogen over time and increases soil acidity.

And harvesting peat moss releases billions of tonnes of carbon dioxide into the atmosphere as peatlands are the planet’s largest soil carbon stock — contributing to climate change. 

Instead, it’s best to use eco-friendly alternatives like Rosy.

2. Compost the Soil

Don’t want to add old soil to your garden or plants? 
No worries! 

Add it to your compost pile instead. It’ll help the pile break down faster and keep insects at bay.

This option is more eco-friendly than throwing it away. Plus, it helps add organic matter, improving the garden soil and plant growth.

3. Store the Soil for Later Use

If you don’t want to use old soil immediately, you can store it for the next plant growing season. 

Just mix the stored potting soil with fresh ingredients (like new potting soil or compost) before using it. 

But how do you store it?
If you have soil from an opened bag, old container, or previous plants, there are some things you should do before storing the soil in a clean, sealable container. 

You should:   

  • Dry the soil if it’s moist.
  • Remove debris, roots, and other dead plant material. You can add these remnants to your compost bin.
  • Take out any insect eggs or cocoons.

If you have unopened bags of old soil, you can store them directly in a cool and dry space.

7 Ways to Reduce the Risks of Using Old Soil

Using old soil comes with certain risks, including:

  • The presence of disease-carrying pathogens like roundworms.
  • Nutrient and mineral deficiency. 
  • Soil compaction.
  • Salt accumulation.

But don’t worry. 

Here’s how to make the soil viable for plant growth:

1. Mix in Fresh Potting Soil

You can refresh old potting soil by blending it with new potting soil. 

How?
Create a 50-50 mix of old and fresh soil to use for your potted plants, mixing the two soils well to prevent compaction and root suffocation.

That said, simply mixing the two soils may not give you the best results. Moreover, using conventional peat-based potting soils is bad for the environment.

So, why not go with an eco-friendly potting mix like Rosy?

Rosy

Rosy offers an organic and clean Earth Positive Indoor Potting Mix free of synthetic fertilizer or fillers.

Instead, it includes pre-activated biochar, nutrient-rich compost, and microbes that provide the perfect balance of moisture and aeration for indoor potted plants.

Add this Potting Mix to old soil or use it directly in your pot or container to raise a healthy plant in no time.

Want to know more about using biochar?
Read our article to discover biochar’s benefits for container gardening. 

2. Never Use Soil from a Diseased Plant

Soil from a diseased plant may carry pathogens that remain in the soil long after the plant has died.

Your best bet is to solarize (baking in the sun) the diseased soil before burying it away from your garden. You may also want to sterilize the pot with a 20%-25% white vinegar solution to kill the pathogens. 

3. Sterilize Old Soil

Sterilizing old soil eliminates harmful elements and pests, like insects and weed seeds, that constrain plant growth.

You can sterilize soil by sealing it in black plastic bags and solarizing over six to eight weeks during the hottest time of the year.

Alternatively, you can wrap the soil in foil and bake it in your oven at 180°F-200°F (82.2-93.3°C) for 30 minutes. Once done, keep it covered until the soil cools.

Note: Temperatures above 200°F destroy the soil structure. 

4. Add Nutrients and Beneficial Microbes to Old Soil 

As old soil might be deficient in plant nutrients, you need to replenish it. 

Here are some ways you can add nutrients and organic matter to soil:

  • Add a handful of a slow release fertilizer like manure.
  • Mix in one part compost for every three or four parts of the old potting mix.
  • Apply a liquid fertilizer like compost tea every two weeks.
  • Mix an organic fertilizer like worm castings or coffee grounds to the top few inches of garden soil.  

5. Reduce the Soil’s Density

Soil compaction is a recurring issue in old soil that contains peat moss or coco peat. These materials have a short lifespan and cause soil compaction when they decompose.

So, you’ll need to reduce the soil’s density for better soil porosity, aeration, and water drainage.

How do you do that?
You can add materials like organic wood chips or biochar to the old soil, which help improve these properties for outdoor and indoor plant growth.  

6. Water the Soil with Rainwater

Soil with a white residue indicates an excessive salt buildup. 

How can you remove that?
Water the soil with rainwater or any water with low salt content (not tap water or mineral water) and let it drain through the soil. You can do this every two months to prevent salt accumulation.

7. Practice Regenerative Gardening

Regenerative gardening minimizes soil disturbance by eliminating tillage — which involves breaking up or unearthing old soil. 

Why?
Tilling destroys pockets of microorganisms in the soil and releases carbon dioxide into the air. 

In fact, a study found that conventional tillage systems have about 40% higher carbon dioxide emissions than no-tillage systems.

Instead, regenerative gardening involves using crop rotation and mulching sheets to nourish old soil without removing it from the garden or container. It helps improve soil health and enhance nutrient and microbe levels.

2 FAQs on Reusing Potting Soil

Here are the answers to two questions on reusing old potting soil:

1. What Should You Remember When Reusing Potting Soil?

Here are four key points to keep in mind when storing and reusing old soil:

  • Remove any dead plant material, debris, and pests from the soil. 
  • Store the soil in dry and cool conditions.
  • Add biochar to reduce the soil density of stored potting soil.
  • Improve soil fertility with compost, worm castings, or any other organic fertilizer.

2. Should You Put New Soil on Top of Old Soil?

The quick answer is no. 

Simply applying a top layer of new potting mix won’t help reduce the compaction or increase the porosity of spent potting soil.

So, when mixing old potting soil with new soil, the new potting soil needs to get deep into the old soil to help plant roots breathe and improve water drainage.

Moreover, you can break up the old potting mix with a shovel before adding fresh soil. This way, the spent potting soil will become less dense and more suitable for growing a new plant.

Wrapping Up

Knowing what to do with old potting soil can help you improve garden productivity.

You can compost the soil, reuse it for container plants, or store it for the next growing season. 

Just ensure the soil is healthy before use by blending it with a renewable soil resource, like Rosy’s Earth Positive Houseplant Mix. And if the soil is beyond help, simply replace it with the mix.

Why not try a bag of Rosy’s Potting Mix today to give your garden a new lease of life?

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