Can I Put Potting Soil In My Compost?


Potting soil can be added to your compost as long as it wasn’t where a diseased flower or plant had previously been growing. It would also be beneficial to pasteurize your potting soil before adding it to the compost. This will help to deactivate any pathogens and kill unwanted seeds.

Potting soil with diseased plants

You should avoid adding potting soil that had previously been the home to diseased plants to your compost pile. This is because the potting soil is highly likely to contain the disease that affected the plant. If you suspect that your potting soil may carry a disease then to ensure this isn’t passed to other plants, this soil should be discarded.

If you’re sure that the soil doesn’t contain any diseased plant debris, or housed a diseased flower then you will be able to add it to your compost. However, before you add it to your compost you should sterilize your soil to get rid of any nasties that may be living in it.

How to pasteurize your soil

Any old potting soil that you wish to reuse in your compost should be treated via a process called pasteurization. You can pasteurize your soil from the comfort of your own home and remove any unwanted inhabitants that might be living in the soil.

Pasteurizing is the process by which gardeners sterilize their old potting mixes. The process helps to increase the health of your soil and ensure the survival rate for new seedlings during the germination period. It will kill off any pathogens, unwanted seeds, and any insect eggs or larvae that have made their home in your soil.

To do this you will need to load the potting soil you wish to reuse into a black garbage bag. Then you will need to place the bag in the sunniest part of your garden as you need to bake the bag in the sunlight. Try to find an area that will be in the sun for the longest amount of time. It’s best to use a black bag as black absorbs more of the heat from the sun. Once that’s done, all you need to do is leave the bag for about a week.

After a week has passed you can now safely add the potting soil to your compost and there will be no threat of contamination. This pasteurization technique replicates what happens in your compost pile but it accelerates the process and removes any chance of contaminating the mixture.


How to replenish the nutrients in potting soil

This may depend on the quality of the potting soil you used, but your soil will likely be depleted of the nutrients it once contained. Even high-quality potting soil can be drained of its nutrients at the end of the growing season. If you want to reuse your soil then adding it to your compost pile, or creating a new one will help the soil build-up its nutrients again.

If you already have compost then you can simply add the potting soil and mix, as long as the soil has been treated for pathogens. Alternatively, if you are looking to build a compost mixture using this potting soil then you should add manure, leaves, coffee grounds, grass, and any old vegetables you have.

Leave it all to decompose in a bin or a pile over the summer ready for use in your next growing season. The decomposition will slow down over the winter so you may need to find a way to keep the compost pile warm. You can do this with a bin with a roof, or using a piece of tarp to cover it.

What should you not put in your compost?

Aside from soil that contains/contained diseased plants, there are a few more things that you should NOT add to your compost pile.

  • Pet faeces. Although manure from farm animals is great for compost, pet faeces isn’t. It may contain parasites or germs that could kill your plants.
  • Meat, fish, eggs, and dairy products. Not only will these have odor problems, they will likely attract all manner of pests that could be harmful to your compost.
  • Coal or charcoal and black walnut tree leaves and twigs. They contain substances that will be harmful to your plants.
  • Fats and oils. You will attract pests and there will be odor problems.
  • Garden debris that has been treated with pesticides. Anything that has been treated with pesticides will likely kill the composting organisms.


Is it OK to put potting soil in my garden?

Potting soil isn’t the best thing to use in your garden, you should consider topsoil instead. The potting soil is best when it is used with plant containers. If you combine your potting soil with the soil outdoors then it can cause your garden soil to dry out as potting soil drains particularly well.

Topsoil is a better choice to combine with your outdoor soil as it contains a wider range of materials. It mixes better with the soil already in your garden. However, if your garden plants are in containers then you should stick with potting soil.

Is there a difference between potting soil and potting mix?

You’ll find in most instances that these two phrases are interchangeable. They both refer to the medium in which plants in a container can grow. However, there is a slight difference between the two.

Potting mix refers to any mixture that is soil-less but was specifically designed for gardening inside containers. Potting soil on the other hand should contain some dirt but is also generally designed for use inside a container.


If you have old potting soil that you want to reuse in your compost, you can. Just make sure to pasteurize before adding to the mixture. If your potting soil had previously homed diseased plants then it should be discarded.

As long as you keep these things in mind, you can reuse the potting soil in your compost and that will help it regain its nutrients.