If you are a gardener, it is likely at some point you will face the dilemma of what to do with the old, used soil from your pots and planters.
This is a common question at the end of the growing season or for those who have small outdoor spaces.
So, what do you do with your potting soil once it has nourished your plants and is dry and infertile?
As you may realize, it is impossible to actually get rid of the soil, as throwing it in the trash only means that it will go to a landfill.
Thanks to the soil cycle, it is likely that the soil will end up back in another garden or field in some years. So, why not cut out the middleman and upcycle your used potting soil at home?
Upcycling your soil has several benefits. It reduces waste, saves you money, and, best of all, is simple.
If you’re ready to consider reusing your old potting soil to create a healthy habitat for your plants and reduce the environmental impact of your garden, here’s how to get started.
Upcycling Your Used Potting Soil
Here are some of the steps to take:
Correctly Dispose of Old or Dead Plants
Allowing the plants to die completely in the pots will make it easier to remove them from the soil.
Shake the dead plants to remove any potting soil that has become attached to the root system, and then throw them in your compost pile.
Their breakdown will add many minerals to your compost, and you avoid creating more waste to send to a landfill.
Remove Any Litter or Other Waste
Pour the dirt through a screen to eliminate any large particles like old root pieces or rocks. Break up any large clumps that remain as old potting soil frequently gets dry and compacted.
This is also helpful in allowing even distribution of any additives with which you may later supplement the soil.
Pasteurize
To kill any lingering pathogens, you must pasteurize the soil. To do this, place the dirt in a metal container (disposable aluminum bakeware works great for this) and cover it with aluminum foil.
Bake your soil at 180 °F for 30 minutes. Take care not to overheat it to avoid damaging the soil structure.
If baking your soil in an oven isn’t practical, you can also eliminate hazardous substances by heating it in the sun.
First, place the used dirt in black plastic bags, garbage cans, or sealed 5-gallon buckets.
While any of these are suitable options, garbage bags are simple to move and position, and the black plastic ones retain heat well.
Place your containers in a sunny position. Inside the bags, the temperature will increase, pasteurizing your soil naturally.
While pasteurization helps to remove pathogens, it is not a perfect process. Therefore, it is best not to attempt to purify old potting soil that housed a sick plant in this way.
In the case of a diseased plant, it is best to throw away the potting soil it was in contact with to avoid spreading the illness to new plants.
Cool and Test
Allow your soil to cool, then test the pH and mineral levels with a soil testing kit. If it is within the desired range, you may only need to add microorganisms or additional soil before reusing.
Alternatively, if the pH is too low or high, you may need to amend the soil with minerals before putting it back in your garden.
Replace Lost Volume
When reusing old potting soil, you must replenish the volume lost over time. An easy way to do this is by combining your old soil with new potting soil in a 50:50 ratio.
You can also add fillers and materials to increase the soil’s drainage capacity, like rice hulls, perlite, peat moss, and coir fiber.
To improve the soil’s fertility, you can use kelp meal, fish meal, or alfalfa meal.
Reintroduce Microbes
Potting soil should be rich in microorganisms to convert organic matter in the soil into nutrients that your plants can uptake and use.
The easiest way to add these microbes is with compost, which can be purchased or made from food scraps and other biodegradable household waste.
However, microorganisms are usually not sufficient to maintain pH balance.
Amend with Minerals
Maintaining mineral balance ensures that the pH of the soil is constantly within the appropriate range.
The most important minerals are nitrogen, phosphorus, and potassium, as plants depend on soil to provide these elements. Others to consider adding are calcium, sulfur, and magnesium.
To determine which minerals to add and how much of each is needed, you can use a soil testing kit.
You may also add fertilizer to your potting soil to help balance the pH but be sure to choose organic materials easily broken down by microorganisms.
If your soil is too acidic, lime can raise the pH. If it is too basic, try adding sulfur or aluminum sulfate to acidify it. Changing the soil pH is known as amending the soil.
Storage
If you do not want to use your upcycled soil right away, make sure it is dry, then store it in a cold, dry area in a sealed plastic container.
Ensure it is free from any insects that may have found it a welcoming habitat before storing it to avoid unwanted future surprises.
Although the above process is relatively simple, if you’re still on the fence about soil upcycling, consider the following:
Benefits of Using Old Potting Soil
Despite its lack of nutrients, aged potting compost still includes perlite nuggets, humus threads, and relatively few weed seeds.
As a result, it is an excellent material for covering newly planted carrots, beets, and other slow-growing seeds.
Likewise, used potting soil is equally valuable to have on hand when moles, dogs, or other creatures dig holes in the grass that must be refilled and mended.
Potting soil is much preferable to regular dirt for seeding new grass. When planted in potting soil, grass seed generally sprouts well with few undesirable weeds.
Perhaps the best part of upcycling potting soil is the benefits to the environment and your wallet. Not only do you prevent unnecessary waste, but you also save money in the process.
Of course, soil recycling is not ideal in every situation. Keep in mind the following considerations when deciding whether this process is right for your garden.
Potential Hazards of Soil Recycling
There are two primary reasons why reusing potting soil can endanger your plants.
First, pathogens—viruses, fungus, bacteria, nematodes, and other disease-carrying organisms—can be found in used soil. These microorganisms can make your plants sick and kill them.
Used soil may also be lacking in nutrients required by plants, which can also lead to disease.
Luckily, the risk of these pitfalls can be minimized by following the upcycling process described above.
You can also do a few other things to increase the likelihood of your plants flourishing in reused potting soil.
- Never reuse soil from a diseased plant.
While you can remove the plant, the infections and other soil problems often persist, increasing the chance that the next plant to reside in this soil will also become ill and die.
- After planting, fertilize your new plants.
While you may have amended your potting soil as part of the upcycling process, exposure to the elements weathers the soil, compacting it and causing nutrients to seep out.
To combat this, use fertilizer to ensure that your plants get the nutrients they require.
Also, consider mixing some compost or new potting mix to your reused soil, especially if you’ve been using it for several seasons.
Adding fresh potting mix will make it more fertile and better at retaining moisture.
- Water with rainwater to reduce salt buildup. Is there white crusting on the surface of the soil in your planters?
If so, it might be suffering from salt accumulation, which can stifle plant growth. Water your plants with rainfall to avoid this problem.
Rainwater often has less salt than tap or well water.
If you enjoy gardening, you can certainly appreciate the beauty of the world around us and probably want to do your part to preserve it.
Upcycling potting soil is a great way to reduce your environmental impact and save some money.
In just a few steps, you can easily prepare the potting soil you already have for reuse in your garden, flower bed, or backyard.
By pasteurizing, replacing lost volume, microorganisms, and minerals, you can breathe new life into your potting soil and reuse it for many years.
Keep in mind that it is never a good idea to recycle soil exposed to a sick plant.
Now that you know how to dispose of potting soil by upcycling it, what will you grow with your used soil?
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