Can you Reuse Potting Soil?
Can you reuse potting soil? That is a great question, especially as commercial potting soils can be so expensive. And even in the most widely available organic potting soils, there are some ingredients that are not considered sustainable.
Can you reuse potting soil? It seems like a simple question, but the answer is not so straightforward.
We need to take a closer look at what is typically in commercial potting soil and what it does.
Today, we will discuss whether or not you can reuse potting soil in your containers and what you should consider before doing so.
What does potting soil consist of?
When it comes to potting soil, the three basic components are peat moss, pine bark, and perlite or vermiculite (to give air space).
Some will include other additives like feather meal, bat guano, lime, sand, etc.
Others will also include chemical fertilizers. Reading the ingredient list on the packaging is helpful for finding out what is in the potting soil you are choosing.
What does peat moss do for potting soil?
Peat moss has many benefits for potting soil, but it also comes with some downsides.
The notable downside is that over time the material will compact and turn into a brick-like consistency.
In addition to this drawback, there are those who feel peat moss should not be used because harvesting from wetlands harm plant and animal life only found within these areas–a debate that still continues today among scientists around the world.
I hone in on peat moss here as I also feel we should eliminate the use of it as much as possible.
Especially as there are so many viable alternatives. That is why I like making my own DIY potting soil.
Can you reuse potting soil?
The basic answer is yes but there are some things you will need to determine and do.
First of all, know that just buying and using fresh organic potting soil for your containers each year is usually the most convenient and widely suggested advice for all gardeners.
But that being said if you want to reuse last year’s potting mix then read on and ask yourself:
Was the plant in the potting soil previously diseased? That is the one time you really should discard the soil or solarize it well.
Plant and soil disease is just not something you want to mess around with.
If you have a pest problem but no disease you can treat the potting soil effectively before reusing it.
How to Reuse Potting Soil by heat treating
Luckily, there are some natural ways to help get rid of the bugs that may be lurking in your used potting soil.
If you discovered any pests on your plants, it’s vital to treat the mixture before using it for next year’s plants.
To begin, clear away any roots, grubs, leaves, and other debris from the old potting soil.
How to pasteurize or sterilize used potting soil:
- Boil it: Place soil in a colander or sieve and pour boiling water over it. Let it drain and cool. This does some completely sterilize the soil but it has worked well for me in eliminating unwanted pest larvae.
- Bake in an oven in a covered pan at 180 to 200 degrees for 30 minutes
- Microwave on high for 90 seconds in a covered container with vent holes then let cool.
note: I personally think that baking and microwaving are more trouble and stinky than it is worth. Fair warning.
The boiling has been more than sufficient for me and can be done outdoors.
If you have larger amounts you can try this:
- Solarizing: Solarizing is a method of sterilization that involves placing old potting soil in tightly lidded, five-gallon buckets or black plastic bags and leaving them in the sun for 4-6 weeks. It’s just hot enough to kill germs and disease organisms within the buckets or bags.
Compost used potting soil
Another way to reuse potting soil is by adding it to your compost pile instead of immediately reusing it in your containers.
If you haven’t started a compost pile because you think it is too hard or takes too much room then you can read how I do it.
How to recharge used potting soil
When reusing soil still in containers there is no need to remove it completely. Take out about a third of the used potting mix.
Add some fresh compost or fresh DIY potting soil to the container and stir it in with the rest.
This will help to add back some of the nutrients that have been depleted and also increase microbial activity which is always a good thing for plants.
It also helps to prevent the compaction that can occur over time.
If you would like to see an example of some containers where I have reused potting soil you can see that in the video.
Have you had any issues with reusing potting soil? Let me know.
