A Guide To Reusing Potting Soil

If you still have last season’s potting soil on hand, don’t get rid of it quite yet! Potting soil can be reused for several seasons, thereby leading to savings and lending the environment a helping hand. 

Potting soil can be reused for 2-3 growing seasons, or even more, as long as you take steps to ensure that pests and diseases don’t persist. You’ll also need to rejuvenate the soil with fresh nutrients and minerals so that your new plants can grow to be big and strong.

You might also consider adding used potting soil to your garden beds, which are sure to benefit from the added nutrients. A big key to success in this approach is knowing how to mix the old potting soil with new constituents that’ll optimize growing conditions. You are invited to continue below, where you’ll learn more about how to reuse potting soil.

How Long Can You Reuse Potting Soil?

You certainly can reuse potting soil, as long as there are no problems with the growth medium (i.e., pests, chemicals that could harm plants, plant diseases). By recycling your potting soil, you’ll help reduce waste at local landfills.

In general, potting soil can be reused for 2-3 years, although there are a few caveats:

  • Tomatoes: Potting soil used to grow tomatoes should not be reused to grow tomatoes for the next two years, although it can be used to grow other plants.
  • Other Plants: You may reuse potting soil as long as you do not plant the same type of plant in the same potting soil during the next growing season.
  • Replenishing Soil: The recommendation is for gardeners to mix in a little bit of fresh soil to the mix every year, so eventually, your original potting soil mix will be replaced.

What Should I Do With My Old Potting Soil? 

It’d be a real shame if you had to do away with your potting soil after every growing season. The good news is that you don’t have to. There are a few viable uses for old potting soil.

You can either reuse the soil in your pots and planters or transfer the soil to your garden beds. In the section below, you’ll find guidance on how to do either of these options.

Reuse The Potting Soil In Your Containers

It’s simply not economical to buy new potting soil every growing season. There’s no reason you can’t just reuse the same soil and the same pots, as long as you take the steps to ensure that the soil is healthy enough for the upcoming growing season. You may also consider sanitizing the pots as well.

Mix Into Your Garden Beds

Alternatively, you might consider mixing the potting soil into your garden beds. The used potting soil will add some valuable nutrients and minerals to the dirt in your garden. It’s important to remember that potting soil isn’t soil at all; instead, it is a mix of natural substances and minerals that optimize growing conditions. The success of your garden depends on nailing down the correct ratio. 

A mixture of potting soil and garden soil can work great in raised garden beds since the fluffy potting soil and heavier garden soil combine to create a lightweight growth medium with plenty of nutrients that plants love. The recommended ratio is five parts garden soil to every one part of used potting soil. If you don’t have enough garden soil, you can always buy bags of it.

How To Reuse Potting Soil

Unfortunately, old potting soil can’t always be trusted. It may harbor pests that’ll decimate your new plants or may simply be lacking the nutrients and minerals that plants need to survive and thrive. Fortunately, you can take many simple steps to ensure that your new plants are happy and healthy in recycled potting soil.

Choose A Container That’ll Last

If you’re going to reuse your potting soil, you may reuse your pots as well. Look for materials that you know will stand the test of time.

Benefits of Terra-Cotta

Terra-cotta pots are highly versatile because their rusty brown color can match every flower or foliage color. These types of pots act as a wick to remove excess moisture away from the soil.

  • Terra cotta pots are also durable due to their thick walls.
  • They are less likely to blow over and break during high winds.
  • Unfortunately, clay does break easily if it is dropped.

Benefits of Plastic Pots

You may turn to plastic containers if you’re in search of greater diversity in terms of design. These pots have some advantages to offer, especially if you are looking for containers with the following characteristics:

  • Lightweight & flexible: plastic pots are easy to move around.
  • Plastic doesn’t break or chip easily.
  • Many plastic pots are made of recycled materials.

Use A Sieve To Clean The Potting Soil

If you are unsure about the quality of the soil, then you are encouraged to pass it through a sieve, like the one found here on Amazon. This will help ensure that larger seeds, roots, and bulbs are removed before recycling the soil. It is not completely necessary, but it certainly is encouraged.

Start By Sterilizing The Soil

Diseases and pests can find their way into the soil during the growing season. If you wish to recycle your potting soil, then you’ll need to sterilize it. Even if you don’t see any pests, you’ll still need to sterilize them. Microbes and bacteria are not visible to the naked eye.

There are two ways to sterilize potting soil:

  • Solarizing: Place the soil in either large plastic bags or 5-gallon buckets and leave in the sun for 4-6 weeks.
  • Baking: Bake the soil in the oven at 200 degrees F for 30 minutes or microwave the soil for 90 seconds.

You’ll also need to sanitize the pots and containers that you plan on reusing. Both the exterior and interior of the pots should be scrubbed with a brush and soaked in a mixture of 1 part bleach – 9 parts water.

Make Sure That It’s Nutritious

Potting soil works so well because it’s jam-packed with minerals and nutrients that plants need for growth. Used potting soil will have lost much of its nutritional value unless action is taken to add nutrients back to the soil. There are several ways that you can do this.

Add Nutrients Naturally Through Composting

One of the best ways to add nutrients and minerals to your garden is by starting a composting pile. You can even engineer your soil to carry specific nutrient ratios based on the types of materials that you are composting.

It’s certainly convenient to just throw your used potting soil on top of your composting pile, as long as there weren’t any pests or diseases present during the growing season. This will easily take care of the nutrient deficiency problems.

Combine Mixtures Of New & Old Potting Soils

You’ll reduce your footprint just by mixing old potting soil and new potting soil in equal parts. This will add back some nutrients to the mixture while also reducing your need for new bags of potting soil.

You’re also encouraged to buy slow-release fertilizer pellets for the mixture. This will help top off the concentration of nutrients and minerals. 

Rotate Your Plants

Some plants require fewer nutrients than others. Hence, it’s recommended that you rotate plants when you recycle your potting soil. For plants that require more nutrients, you’ll need to either use new soil or rejuvenate the growth medium using the methods described above.

  • Vegetable plants in the same family should not be planted in the same soil year after year.
  • Tomatoes are more prone to diseases than many other plants.

Why You Should Water The Soil With Rainwater

If you notice white crusting on the soil’s surface, then this is a sign that you have used too much tap or well water. The white crust is a buildup of salt from the water supply. Fortunately, there is a viable solution for watering the plants in a way that won’t lead to any further salt encrustation. 

The solution is to collect rainwater to water your plants. This works because rainwater tends to have a lower salt content versus well water or tap water. The most convenient method is to purchase a rain barrel, like the one found here, and place it under one of your downspouts.

Storing Potting Soil

You might consider reusing potting soil for the next growing season. The big question here is: do you simply keep the potting soil in the same pots, or is there a better method for storing the soil in preparation for the next growing season? You’ll find answers to these questions in the following section.

First of all, it is recommended that you store the soil in freezing conditions if you can. This is because freezing temperatures discourage pests from invading the soil before you can use it for the next growing season.

  1. Place the potting soil in airtight containers.
  2. Separate soil into two categories: vegetables and flowers. By doing this, you will discourage the continuation of diseases known to exclusively affect flowers and vegetables. The soil used to grow vegetables this year will be used to grow flowers next year, and vice versa.

Why It Might Be A Good Idea To Place Used Potting Soil At The Bottom

You might consider simply placing the used potting soil at the bottom of the container rather than at the top. This is a more viable solution than placing it at the top for several reasons:

  • If you place the used potting soil at the bottom of the pot and new soil at the top, you won’t necessarily have to refresh the nutrient content.
  • You’ll still reduce your need for new bags of potting soil.
  •  You should be able to optimize the soil drainage conditions.

How To Optimize Soil Drainage With Used Potting Soil

In many cases, the overall condition of the potting soil will have changed after it has already been used. In this case, it may make the most sense to use other growth mediums in combination with this potting soil to optimize drainage conditions for the specific plant you are growing.

It is imperative to pay attention to drainage demands as you plan to use last year’s potting soil with different types of plants. Some plants, such as succulents, do not do very well in moist soil and will undoubtedly require a change to the potting mix. 

Here are some tips for optimizing growing conditions with reused potting soil:

  • Sand is added to potting mixes for cacti and succulents to improve drainage.
  • Perlite is a volcanic rock that is used to improve drainage and aeration of potting mix.
  • Vermiculite can be added for plants that prefer wet soil. Peat can also be added to the mix to improve the soil’s ability to retain moisture.

How To Remove Pests From Potting Soil

Inevitably, you will eventually run into issues with pests in your potting soil. Luckily, there are many viable solutions for removing pests from the potting soil. Below you’ll learn how to easily remove even the most persistent of pests and diseases, so that your potting soil may be safe for reuse.

  • If you notice flying gnats around your plants, you are encouraged to place yellow sticky traps near the pots.
  • Pesticides such as acetamiprid and bifenthrin work well in extreme situations. 
  • When using pesticides, make sure that you follow the instructions on the bottle for application.

Final Thoughts

You can reuse your potting soil from the last growing season as long as you take a few simple steps to ensure that the soil is healthy. You might consider adding constituents like sand, perlite, or vermiculite to the mix, which will improve the potting soil to meet the daily moisture preferences of whichever plant you are trying to grow. Many more helpful tips on how to reuse potting soil are included in the sections above. 

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