Reusing Potting Soil With A Soil Scientist

Reusing potting soil every year for container gardening
Some of the containers I have reused potting soil in.

Potting soil is an absolute necessities when growing indoor plants or even container gardens. Potting soil however can get expensive ranging anywhere from $30 a bag to $50 a bag based on the quality. The answer to reusing potting soil is based on a few factors such as smell, structure & age. Not to mention the fact that is not a renewable resource and therefore as a human of earth we need to take that into consideration.

My name is Ashley and I’m a soil scientist. I truly take great joy in making content that debunks the myths of gardening with science. Let’s look at what it takes to properly revitalize a peat moss based soil.

Technically Peat moss is Soilless

When we’re looking at peatmoss a soilless medium we need to take into consideration a few things. It’s made of organic material so therefore it can decompose over time. This is a major difference when compared to earth soil which is made of in organic material that does not decompose overtime.

Reusing Potting Soil And What I Do In My Own Garden

Natural Soil Vs. Peat Moss

Natural soil is essentially a large rocks being turned in to smaller rocks through processes of weathering. Weathering can consist of sun, water, wind and various other mechanical methods. That take place over hundreds of thousands of years. Using natural soil in a pot situation is less than ideal. The reason for this is because it tends to compact reducing the porosity in the soil. This lack of porosity and aerobic environment which ultimately it will harm the plants.

In an anaerobic environment we end up with the notorious root rot. In order to prevent the we use potting soil which is made of peat moss for coconut coir. Both of these organic soilless mediums can be reused year after year with some minor steps.

What Happens To Potting Soil Over Time

Because peat moss is an organic material over time it can degrade. Especially if you have a healthy soil high and microbial activity. Microbes cycle organic material and turn it into fertilizer. Having a healthy microbial population is essential to proper nutrient cycling and ultimately delivering a vast array of bioavailable nutrients to the plant.

The best way to continue to develop the microbial communities is through reusing soil that is already high in microbial populations. When were using peat moss based soil we are essentially inoculating our new soil with our old soil. This inoculation is going to spring board your garden into higher yields.

When Is It Time To Renew Potting Soil

To understand whether or not you’re putting soil is up for renewal is through feel. If your soil has very little structure and you go to squeeze it and it kind of collapses on itself. Then this is a sign that it is time to fluff your potting soil.

The way to see if you’re putting soil is eligible to be reused is through smell. You will need to take some of your old potting soil and give it a sniff. If it smells rotten or rancid in the kennel longer be reused. This means it has a high level of anaerobic bacteria which can cause route right. This soil is best used in a raised bed or in the general garden outside of the container garden setting.

If the soil smells rancid and rotten it should not be reusing in a container garden setting. Consider using it as a mulch for the open garden.


If the potting soil smells fresh and like earth this is the perfect candidate for reusing. I have been reusing potting soil up to five years old as it has held both its structure and an earthy sent. The reason for this I believe it is due to proper appointments of my soil and ensuring things such as overwatering do not take place.

Disease, Pests And Problems In Old Potting Soils

One last consideration before deciding to reuse this potting soil is whether or not there has been past diseases. If you had repeated seasons of things such as thrips fungus gnats or powdery mildew do not reuse this potting soil. The soil may pass the feel test and the smell test it most definitely does not pass the disease free test.

Problem diseases or fungal infections tend to harbor in our soil. And particularly in organic soil’s such as pest moss. Oddly enough some of these can make it through a Canadian winter despite the fact that we think the outside is dead.

Once you ensure that your peatmoss based soil passes the feel test, passes the smell test, and passes the disease test. It is time to begin their free by the way station process.

Reusing Potting Soil – Debris Removal

First off start by dumping all your potting soil into a reservoir. I personally enjoy using kiddy pools because they tend to be small and light weight. From there you are going to sift through your soil you are going to find the clumps and break them up.

You are also going to find some other things such as children’s toys that may have landed up in the mix, and left over plant pieces. Remove the children’s toys and be sure to put them in a storage area for the children’s Christmas gifts this year. I’m sure they won’t notice.

And for the leftover plant bits. You’ll want to rip these plants apart and try to use them in the new soil mix as much as possible. This is free future potting medium that not only contains all the fertilizer you said to your plants from the air before but also organic carbon which is essential to plant growth.

Think About Adding Pumice Or Perlite

Once you’ve gotten all the chunks down to a nice smooth texture it Time to start adding. One of the first things you should look for is left over perlite. This is that white all stuff that you find in peatmoss based soils. You should be able to see that approximately 5% to 10% of your soil is perlite.

If it is less than that we will want to add some more. Think about potentially using pumice instead of perlite as it tends to last longer. This is due to an in organic natural state that tends to avoid weathering or break down. Perlite very easily tends to compact and disappear over time.

Renewing Old Organic Material In Potting Soil

Once you’ve added your perlite or pumice it is now time to add some organic material. What do you choose is completely based on personal preference compost or manure will work. What form of compost or manure you use ultimately doesn’t really matter. I know that’s an unpopular opinion, but in my professional observation there is very little to no difference in yield production between types.

Per kiddy swimming pool volume (approximately two bales of potting soil) you will want to add two bags of compost or manure. Do not add more than this as it will cause runoff and ultimately your hard earned money will be in the city sewer. The use of Manure and compost in the garden is a good thing, however it is important to remember the manures and compost can cause eutrophication.

Eutrophication is a fancy word for The green algae you see in ponds and lake bodies. This suffocates fish and plant life in water bodies around the world. Be responsible with how much you decide to add to your garden.

Pro Tip Additions

If you want to get really nerdy consider adding mycorrhiza to the potting soil to help build a web of fungi. This web will ensure better water utilization and even some free fertilizer.

Also try mulching the potted soil surface with bark to hold moisture in place. This is valuable for the later in the season when water is easily evaporated from the soils surface.

I truly hope you found this helpful! If you’re enjoying the gardening in Canada blog be sure to hit that share but and post it wherever your heart desires. If you are looking for more on container gardening check out this post here