Does Potting Soil Go Bad?

potting soil

Growing houseplants is a fun activity. There is something incredibly rewarding about nurturing plants. Often, we are about to repot a plant from the store or repotting a growing plant into a bigger container and we find old potting soil stored on our shelves. Is it still usable?

You would think the answer is simple but in reality, it’s not. Many nuances are involved with potting soil and its shelf life. So, does potting soil go bad?

In this article, we will share everything there is to know about potting soil – a shelf life with an opened bag and unopened bag, how to store potting soil properly and how to sterilize potting soil.

How Long Does Potting Soil Last?

On average potting soil will stay fresh for 6 months in an opened bag. After one or two years, potting soil can still be used in an unopened bag. This depends on the conditions it is stored in.

In high-humidity environments with poor ventilation, potting soil degenerates much faster and will induce mold growth. Potting soil consists of mostly peat moss, which will chemically change over time.

Careful indoor gardeners will have noticed, that on the bag of the potting soil, an expiration date is written. Once the date has reached for an unopened bag, you shouldn’t use it anymore, unless you are willing to experiment with the lives of your houseplants.

How To Know If Soil Has Gone Bad?

Potting soil can change color if left unchecked for a long time. Green or yellowy material can appear on top, which is mold.

Insects being attracted to potting soil is also a bad indication, bugs usually gather around decomposing peat moss. If this happens, it’s best not to use this soil.

Potting soil can also start smelling bad, like rotten eggs, which will also indicate you cannot use that potting soil anymore.

plants in soil

Storing Potting Soil

The correct way to store potting soil is in a well-ventilated room with low humidity. This way you can be sure that once you use the potting soil, your plants will thrive.

Once you have opened a bag, you should keep it air tight and in the same conditions as any bag of potting soil. It would be wise to duct tape the bag back together and place it in an airtight container.

When storing unopened or opened bags of potting soil, ensure that the bag is intact, with no holes or openings.

Old Potting Soil

What should you do with potting soil that has gone bad? There are two choices.

#1 Add to Compost

Potting soil that is not infected by bacteria or is not a home to fungus gnats, can be added to the compost. It’s an easy way to have more compost at your disposal.

#2 Rejuvinate

Old soil can be rejuvenated, but it requires some effort:

  • Take old soil and spread it on a tarp
  • Place the soil under the sun
  • Water the soil to flush out unuseful ingredients
  • Mix the soil with fresh potting soil, half rejuvenated half fresh
  • Test the pH of the soil, it should be around 6.5
  • Add a little fertilizer to the soil
  • Let the soil sit in the sun for two weeks

Sterilizing Potting Soil

If you want to be extra careful with new plants, it is a good idea to sterilize the potting soil beforehand. Unfortunately even freshly packaged potting soils can have pathogens and pests inside, which can be annoying to deal with afterward. There are two easy ways to do this at home.

#1 Freezing

Freezing potting soil in the fridge is a good way to sterilize the soil. Fungus, pests, and pathogens are not well-equipped to deal with really low temperatures. Keep the potting soil in the freezer for a few days (3-5).

After taking the potting soil out of the fridge, let it thaw out naturally at room temperature and add some organic material to amend the soil.


#2 Using a Microwave

Microwaving food or soil is not so different in terms of killing pathogens. Microwaving something will increase point temperatures in the soil to really high temperatures for short periods, which pathogens and pests will not survive.


Final Words

Yes! Potting soil does do go bad, but there are ways to get around it. The right way of storing soil can go a long way. Old potting soil can be rejuvenated or added to compost. Also, it might be a good idea to sterilize your soil before use, to increase your chances of success with indoor gardening!

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