If you are a plant lover like myself, you are constantly redecorating and reorganizing your little green friends. All of that includes repotting as well. Now, the question is, what to do with used potting soil?

Can you reuse potting soil? In short, yes, but make sure you follow these steps while doing it:

  1. Remove the old plant
  2. Fluff the soil
  3. Replenish lost nutrients
  4. Mix it well
  5. Reuse the soil

We’ve seen it is possible, but now let’s elaborate on how to reuse potting soil.

Remove the Old Plant

The first step is pretty obvious – you’ll have to take out the old plant (or what is left of it) to reuse potting soil.

Now, when I say the old plant, I mean all of the plant matter as well – roots, leaves, twigs, etc.

Carefully remove all the leftovers.

This way, you avoid letting any unwanted ‘guests’ and damaging materials stay in your soil.

Fluff the Soil

Although it seems like it isn’t of much importance, fluffing the soil is one of the main steps if you want to reuse potting soil. Shaking will let you remove any possible residue from the previous plant.

Fluff the Soil

On the other hand, you want to stop the soil from lumping. Lumps are bad for water running.

Also, they are pretty hard and compact, so they often don’t let the roots develop nicely if found on their way.

Since you are trying to rejuvenate old potting soil, keep in mind that a lot of nutrients have already passed through that soil.

Logically, many of those nutrients have been gathered in one place (the soil layer that has been on the bottom of the pot, probably).

In the end, you are doing this to prevent any bugs or parasites from transitioning to your new plant.

So, shake it till you make it!

Replenish Lost Nutrients

Although the answer to the question ‘can I reuse old potting soil’ is basically yes, there are some ground rules you must follow.

First of all, the plant extracts all the valuable ‘food’ from the soil.

Through time, the level of nutrients decreases (especially if you have potted a plant that doesn’t need any extra fertilization, thus you haven’t fed it; here, I would like to add that I recommend using organic or non-organic fertilizers on every house plant since they are already in loss, not living in natural, but rather simulated conditions).

The new plant will have a hard time thriving in low-nutritional soil. This is the reason why you should replenish all the lost nutrients.

The process of rejuvenating old potting soil is exactly what it sounds – you’ll need to add some new, young energy. That young energy comes from fresh soil. You can buy it from your local flower shop and mix it with the old soil.

If possible, you should always try to buy organic soil. I would like to emphasize that this is a very important step especially if you are using soil that has been in use for over a year.

It will usually form a white crust at the top, so you will have to make a mix of 50 percent new and 50 percent old soil.

Another solution is to add some natural compost (that you have created yourself, preferably).

Pro-Tip: If you like, you can add some plant food or fertilizers to your mixture, just to refine it a little.

Slow-release fertilizers are also a great choice!

You can always make a little research on natural fertilizers that you can produce yourself – they are both beneficial for the plant, and useful for the planet since you are lowering the amount of garbage you produce.

Mix It Well

Now that you have added fresh soil, it is time to blend the matter. Always use your gardeners’ gloves when doing this!

Sometimes it happens that there are dangerous leftovers in the soil, such as sharp branch parts, thorns, or even glass pieces or other possibly threatening matters.

Mix it very well, until you can’t any longer differ the old from the new soil. All the nutrients must be equally deployed for the plant to grow properly.

Reuse the Soil

Having prepared the soil, you may now use it as you normally would.

In addition, I recommend using revitalized old soil for low-maintenance plants that don’t require high-value soil.

Pasteurizing

Some experienced gardeners suggest another step between the third and the fourth one (replenishing and mixing). Still, not everyone uses it, which is why I’ve decided to explain it separately.

I’m talking about pasteurizing.

I am sure you all know what is pasteurizing in general (if nothing, you’ve heard it in the context of the food industry).

Anyway, when it comes to gardening, pasteurizing has the same meaning –  to heat something at a controlled temperature for a fixed period to kill the bacteria.

So, if you are not sure can you reuse soil, this is the way to go. Now, there are two ways to pasteurize the soil:

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1. Baking in the sun

This is a more natural and less stinky way, so I gladly recommend it. The problem occurs if you want to reuse the old soil during wintertime, or if you live in an area with little sunlight.

Anyway, if you have the right conditions, here is the way: You will need some black plastic bags. Put the soil in the bags, close them, and leave under the sunlight during the hottest days of the year.

Leave them like that for four to six weeks. The pasteurization process will occur pretty quickly since the temperature inside the bag will be much higher than outside.

Of course, you can use some other containers, like plastic boxes, but bags are better for a few reasons.

  • First of all, they are easier for maneuvering – you can easily relocate them.
  • Also, since they are black, the pasteurization will happen a little quicker than if they were in a see-through box, for example.

This is where the physics knowledge comes out – since black is actually the absence of all the colors, it literally ‘collects’ the light, raising the temperature in the bag faster.

If you think about it, you are recreating the same process that happens when you are composting.

This way, you are just accelerating it a little bit.

2. Baking in the oven

Although you are a gardener, you can play in the kitchen as well.

If you don’t want to wait for a month or so until your soil is ready, you can pasteurize it in the oven as well! A microwave is also an option.

Bake it at a 200degree temperature for 20 minutes to half an hour. Be prepared for a very unpleasant smell!

Also, there is a chance of overbaking the soil and killing the valuable ingredients that way. So, be very careful!

The Risks of Using Old Potting Soil

Sometimes the old soil may contain harmful pathogens like bacteria, viruses, or fungi. The problem here is that most of these pathogens aren’t visible to the naked eye.

They may cause major problems to the new plant, especially if it is a young one – it may kill it in no time. The low mineral level might be a problem, particularly if you are reusing the soil for plants that require high nutrition.

This is the reason why I have developed a ‘circle’ in potting. Namely, I tend to use purely new soil for high-maintenance plants.

Then again, when I am planting cacti, aloe vera, or similar plants that require low-nutrition soil and little care, I will reuse the old soil. Of course, you can’t always ‘program’ the repotting process, but you can try to establish the ‘circle of reuse’.

How to Minimize the Risk

Some ways may help in minimalizing the risk of possible harmful effects of reusing old soil.

1. Try to skip reusing soil with roots

There is no reason to leave any of the leftovers from the previous plant, so try to remove them as much as you can. Besides, because all of the residues are dead, it will shortly begin to rot and possibly intoxicate the soil (and the plant, of course).

2. Use fertilizer

If you haven’t added any new soil to the mixture, it is for the best to at least add some fertilizer as soon as you plant the new greenery.

3. Reduce the salt built up

There are two ways to do this.
The first one – use rainwater. It has a lower level of salts than tap water. Besides that, it is free from some harmful substances found in water (chlorine, for example).

You can take your pots outside while it is raining and let the plants soak up nicely. But, be careful! If it is too cold outside, the weather may harm some of the more delicate plants. You can also collect rainwater.

If you don’t have the conditions to do it, the best thing to do is simply use filtered water. Distilled water will also work (it has no minerals, but also no harmful materials).

Another way to help the new-coming plant is to place the old soil at the bottom of the container, and the fresh one above it.
But, if you decide to do this, use as little as possible of the old soil.
I have already emphasized the importance of blending the two matters.
If you still decide not to mix the old with the new soil, try to use a much bigger percentage of the new one and lay it over the old soil.

Benefits of Using Old Soil

Let’s take a look at some of the benefits of using the old soil:

  • Lower costs are the main benefit since you will save quite a few pennies on the soil.
  • It will save you time if you have prepared the soil earlier since you won’t have to waste your time going to the shop and picking out the best option.
  • If you have enough boxes, the soil is easy to store over the winter, even outside.

These are the most important benefits, but, as previously said, you should be careful when reusing potting soil.

Other Ways How Can Potting Soil Be Reused

If you are not thrilled with the idea of your new plants being planted in old soil, there are still ways to reuse it.

You can spread the old soil around trees, add to compost, or use for planting vegetables outdoors (just lay it to the ground). Another way is to work it into flower beds.

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In the end, you may as well use it for pure decoration purposes and fill up the holes in your garden or backyard.

Frequently Asked Questions

Can I Reuse Soil from a Dead Plant?

The short answer would be no.

Why?

Well, the plant is dead and gone and taken out of the soil. But the possible pathogens and other damaging substances may still be in the soil.

What to do with old potting soil?

Throw it away! Although it seems like a waste of money, trust me, it can do more harm than good.

Can You Reuse Potting Soil from Last Year?

Yes, you can.
The process is pretty much the same as I have already described.
The only difference is you will have to make sure you have sealed it properly.
Namely, if the box isn’t sealed, pathogens may get inside, especially if you are keeping the soil outdoors.

Pro-Tip: When leaving the soil for the next season, make sure you first clean it and remove all the excess plant parts and any other ‘intruders’.

Can I Reuse Potting Soil with Roots?

Well, the best answer is – try not to.

I will explain it.
As I have already mentioned, it is for the best to extract all the residue from the previous plant.

However, sometimes it isn’t possible to remove all the root hairs. If there are some left, you must mix the soil with a fresh one.

Also, you shouldn’t plant the same plant species since the rotting root hairs might affect it. So, try and plant different greenery.

Summary

There are ways to save some money and reuse old soil. While doing it, make sure you have extracted any eventually harmful residues from the previous plant. Make a fresh new mix of the old and new soil and enable your plants’ growth and prosperity that way.

In the end, I would like to add that there are gardeners who simply reuse the old soil without adding or extracting anything from it.

I don’t recommend this type of reuse since it may be pretty damaging, not only for the new plant but for the rest of your indoor plants as well.

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