The Truth Behind When You Can Re-Use Potting Soil


Do I need to change potting soil every time I redo or refresh my container?

You do not need to change the potting soil every time in your container. It is not necessary, however, it is best to pull out and do a ‘reset’ of your potting soil every year by following the suggestions below in “How can I reuse potting soil“. If you have potting soil that is breaking down to become very dense; soil that the perlite, the little white balls, has broken down into dust, then you do need to change out your potting soil. I do recommend for the best results with your plants to change out the potting soil completely every other year at least.  This is why.

Why Change Potting Soils In Your Containers.

-Good potting soil has micronutrients that can be used up, that are not added back in with your standard fertilizers that focus on NPK (Nitrogen, Phosphorus, Potassium).  Fresh potting soil gives your plants some fresh soil to thrive in, removes any source of overwintering insects that might be in the soil, or any fungus disease spores which may be harboring in your soil. It doesn’t hurt to change your potting soil every time you replant in your planter.

Do I need to put in more fertilizer?

-Depending upon what type of fertilizer you use and how long it’s been since you have fertilized in which season is going into matters about fertilization.

Potting Soils With Slow Release Fertilizer In The Mix

-It also matters what type of potting soil you’re using, if you’re using a regular average potting soil that contains time-release fertilizer usually the time-release fertilizer is only good for about three months. That is three months from when it got wet.   It is rare that a retailer understood, or cared that something like potting soil needs to be kept dry, and dry storage space at a retailer is limited. I much prefer for you to use a time-release fertilizer, such as Osmocote, from the container and add it yourself to your potting soil rather than buying the potting soil with the fertilizer in it.

Click Here to see Osmocote on Amazon

The reason why is, the fertilizer in those are water-soluble, so every time the potting soil gets wet whether it is at the manufacturers, it’s transported to the store, or where it is stored at the store, or where you have stored at home. If the slow-release pearls get wet, they start to release that fertilizer, which then gets washed out of the soil even before you get it from the bag to the planter. You don’t know if there is any fertilizer value left, or if there is, for how long.

Does it Matter What Brand Potting Soils I Use?

-Many of the very high-quality potting soils that are based on things like composted Forest Products, and additives like earthworm castings, and bat guano, and other organic fertilizer bases already have a good fertilizer base to start with for at least your first month. how long pants upon exactly what’s in your potting soil, exactly what you planted, and exactly what season it is for how much and how quickly that fertilizer is used up.

So in a nutshell, have a light hand the fertilizer when you pot up in a planter and plan on fertilizing a month in.

Changing out your potting soil does not necessarily mean buying new potting soil.  See below on how to reuse potting soil.

When re-potting, here is an article I wrote about the controversy of putting rocks, or not at the bottom of the container.

When re-potting plants into larger containers, yes, add new, fresh potting soil to existing soil, or reuse other potting soil with some amendments listed below.

Related Questions:

How can I Reuse Potting Soil?

Soil doesn’t expire or go bad.  The time-release nutrients can run out, or if stored soggy it can sour, but these issues can be remedied.  If reusing in containers again, put all your used potting soil in a larger storage container. Sift out any roots, or stray rocks.  Dampen, close up in a bag airtight and put in the baking sun for a few days to get really hot to cook off any disease organisms or insect eggs.  Add some lime, rock phosphate, worm castings, compost, and organic all-purpose fertilizer to the mix stir, and evaluate. If it is dense and heavy (as compared to your experience with potting soils) add perlite, vermiculite, or expanded shale to the mix.  

How do I store potting soil for the winter?

To store potting soil, it is important to keep it contained, dry, and sterile.  Store it in a covered waterproof container without access to insects or other critters.  I like to use plastic totes with firmly locking covers. Stored in their own bags is allowing mice or snakes, whether through a small hole tear or chewed through by mice.  Yes, mice could chew through a plastic tote as well, and if you are in an area where mice are a larger problem, upgrade to a galvanized container. Any container needs a tight lid to keep the mix dry.  Wet potting soil releases time-release fertilizers, promotes decomposition (changing the mix from its crafted qualities), and promotes mold, bacteria, and fungi. These you do not want active in your container mixes.  You want your mix to be a safe and easy environment for young plants to root in and grow before they need to put resources towards competing with molds, bacteria, and fungi.

Can Potting Soil Get Moldy?

Yes, but it is not always a problem.  Mold spores are everywhere, all the time.  Some are dangerous, most are just a nuisance.  They do not grow unless the conditions are right to grow.  If the mold is growing in potting soil in a bag, let dry out and expose to the sun.  As long as the soil structure remains well-drained, you are fine. If the soil has been under anaerobic decomposition, without oxygen, the pH could have dropped from the production of humic acids in those conditions.  If you are not sure, mix with fresh potting soil, or add to your garden beds, use elsewhere rather than your pots. But that is not a reason to toss the soil. Mold and fungi are normal, natural parts of soil.

That being said, if mold starts growing on your soil while it is in your pots, that is a reason to check what is happening to encourage that mold or fungi growth.  Most plants do not like the conditions that mold and fungi like. Wet and cool.

If you see these growing on your soil that your plants are IN, that is a warning sign that the soil is too wet and/or compacted for most plants to grow.  OR you do not have drainage at the bottom of the pot. Check the drainage hole, make sure it is not plugged. If no drainage hole, there is your culprit.  Re-pot into a container with a drainage hole. Use it as a warning to change those conditions before you lose your plant.

To deal with the active mold in your soil, sterilize, coo, the soil in an oven at 200 degrees F for an hour.  Warning, this will stink up the kitchen. Another alternative is to bag seal the soil and put it in hot, baking, strong, full sun for a couple of days until the heat from the sun does the trick.  

Also, a solution of hydrogen peroxide and water can be sprayed on soil and plants, see here for the correct ratio, or cinnamon can be sprinkled on the soil.  Be aware of cinnamon before you do this about the different substances called cinnamon because not all of them are antifungal.


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