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Potting soil is an absolute necessity 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 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 over time.
Natural Soil Vs. Peat Moss
Natural soil is essentially a large rock being turned into smaller rocks through processes of weathering. Weathering can consist of sun, water, wind and various other mechanical methods. That took place over hundreds of thousands of years. Using natural soil in a pot situation is less than ideal. The reason for this is that 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 this, 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.
Can You Reuse Potting Soil Each Year?
Yes, and it is actually advantageous to do so. Old potting soil is alive with microbes that help manage pests and cycle nutrients. Reusing potting soil can help you maximize your growing conditions. There are a few things you can do to help make reused potting soil better.
Recharging Old Potting Soil Steps:
- Check for disease and pests. If the previous plant had issues compost the old potting soil rather than trying it recharge or sterilize it.
- Remove Debris – roots, shoots and leaves should all be removed and composted. These can tie in nitrogen and reduce its availability to the plants.
- Break up into a homogenous mix with no large clumps
- Incorporate fertilizer of your choosing such as granular or vermicast
- Assess your pore space holding components. Perlite and pumice will break down with weathering. add more if you notice less than 15% of the soil contains these parts.
- Mix in biological pest controls such as nematodes to help reduce populations of ants, thrips, gnats etc.
- Use lime to help increase your potting soil pH and allow for more bioavailability of nutrients.
- You can also incorporate microbes such as beneficial bacteria and microbes.
What Happens To Potting Soil Over Time
Because peat moss is an organic material over time it can degrade. Especially if you have healthy soil with high 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 we’re using peat moss based soil we are essentially inoculating our new soil with our old soil. This inoculation is going to springboard your garden into higher yields.
When Is It Time To Renew Potting Soil
To understand whether or not you’re putting soil 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 the route right. This soil is best used in a raised bed or in the general garden outside of the container garden setting.
If the potting soil smells fresh and like earth, this is the perfect candidate for reuse. I have been reusing potting soil up to five years old as it has held both its structure and an earthy scent. The reason for this I believe 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 have 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 most definitely does not pass the disease-free test.
Problem diseases or fungal infections tend to be a harbour in our soil. And particularly in organic soils 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 peat moss-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.
How To Revitalize & Reuse Potting Soil
To revitalize and reuse potting soil you will want to remove debris, aerate and add new organic materials. Other things to consider would include granular fertilizers, beneficial microbes and biological pest controls.
How To Reuse Potting Soil With Roots
To reuse potting soil with roots you want to break up the masses. Whatever can be broken down into a homogenous mixture can be moved into a new pot. Any roots and stems that will not break down or are not the same consistency as the potting soil should be composted. These large roots will lock up nitrogen and steal from the plant’s nutrient needs.
How To Store Used Potting Soil Over The Winter
Placing your potting soil in a sealed container over winter is the best form of storage. This will allow the potting soil to remain free from gnats, thrips, ants etc. If you have too much potting soil to place in sealed containers store the potting soil inside the regular pots with drainage. This will prevent anaerobic conditions which can ruin your potting soil.
You will want to store it in a sealed container to avoid ants and other critters using the medium. If this is not possible leave the potting soil inside the original containers so long as they have drainage. You may want to consider placing a plastic bag or cover over the pot if there is no drainage to avoid standing water buildup.
Avoid storing your potting soil anywhere that does not have drainage and can collect water. Potting soil that sits in water can develop anaerobic bacteria that can cause root rot. These warm moist conditions will also result in amplified rates of decomposition. Remember potting soil is an organic material and will decompose over time.
What To Do With Potting Soil At The End Of The Season
You can simply leave the potting soil inside of its original pots or place it into a sealed container. A sealed container will help ensure you do not have things like ants, thrips, gnats, etc. move into the potting soil
How To Sterilize Used Potting Soil
Avoid sterilizing used potting soil whenever possible. Sterilized potting soil no longer contains vital microbes that cycle nutrients and even fight pests. Potting soil should always be full of life to maximize your plants healthy. If you have issues with your used potting soil and want to sterilize it consider composting the infected soil.
This will remove any of the problems without wasting the potting soil. The other method would be to introduce beneficial microbes, nematodes and mites. This will help to balance out the harmful critters and maintain a healthy used potting soil.
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 lightweight. 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 leftover 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 a 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’s Time to start adding. One of the first things you should look for is leftover 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 inorganic natural state that tends to avoid weathering or breaking 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 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 that 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 for 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 potting 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 surface of the soil.
I truly hope you found this helpful! If you’re enjoying the gardening in Canada blog be sure to hit that share and post it wherever your heart desires. If you are looking for more on container gardening check out this post here