How Long Does Potting Soil Last | Does It Expire Or Go Bad

For thousands of years, humans have been practicing the art of container gardening. From as far back as the ancient Egyptians to the hanging gardens of Babylon to the 1990s, when our modern-day ideas of container gardening came into popular consciousness. 

For all that time, we’ve been doing our best to try and replicate the type of fertile soil, in our pots and other containers, that nature herself seems to produce with such ease. A large part of that effort has been asking questions like, how long does potting soil last? And does it expire or go bad? 

If you too are seeking answers to these questions, you’ve come to the right place. The longevity and quality of our potting soil will depend on a number of factors. Which I’ll be discussing more in-depth, so read on. 

Does Bagged Potting Soil Expire 

Every spring, bags of potting soil fly off the shelves. But, what if we don’t use it all or have unopened bags left over? Most of us usually store it until we need it. But, how long will it be good for? Well, that all depends on what’s in it. Bagged soil containing peat moss, for example, will degrade much faster than soil without. 

This type of plant material, typically used to increase moisture retention in loose substrates, will decompose far faster than soil, alone. Even in an unopened bag. Within 6 months, that decomposed matter will seep into the rest of the bag, contaminating its contents. Where bags of soil without peat moss, opened or unopened, can last for up to two years. 

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Is It Okay To Use Old Potting Soil 

Plants will naturally absorb all the nutrients they find, resulting in our need to supplement with fertilizers. Re-used potting soil may end up lacking in all that plants need to thrive. It can also develop harmful bacteria that can only be removed through the process of sterilizing the soil. 

Old potting soil can be rejuvenated by:

  1. Spreading soil evenly across a plastic surface (like a tarp) and exposing it to several days of full sun. This should eliminate any existing bacteria in it. 
  2. Mixing in some nutrient-rich compost. This will increase fertility for both plants and subsurface microbes. 
How Long Does Potting Soil Last Does It Expire Or Go Bad 1

Does Potting Soil Go Bad Or Go Off Once Opened 

Every living, breathing organism has a shelf life, including fertile soil. How long we can maintain the effectiveness of our potting soil depends on a number of factors. While it’s true that unopened bags last longer, soil in opened bags can remain vital when proper storage measures are followed.

Buying soil without peat moss is the first step. As mentioned, mosses will break down faster than the soil itself, spreading gases and other harmful materials throughout. An opened bag of moss-less soil can last for up to two years.

But, if stored in a damp area, unhealthy bacteria growth may ensue. Storing unused soil in sealable plastic containers will keep it dry and perfectly re-usable in spring. 

Mouldy Potting Soil 

While many lie dormant, the most common, active mold found in potting soil is a white, fuzzy-looking type known as a saprophytic fungus. While unsightly, it’s harmless to plants and forms in over-watered soil with insufficient drainage or bags of soil that are stored in damp areas. 

White mold actually assists in breaking down matter, like fertilizer, by consuming it and re-releasing it, making vital elements more accessible to plants. Its appearance often serves as a helpful indicator that your plants are not getting what they need. Like better drainage, more sunlight, and easier access to nutrients. 

Decomposing Peat Compost 

The overharvesting of peat moss has compelled many countries to ban it and many companies to offer new products without it. Originally used to increase moisture retention and soil aeration, peat moss-based potting soils have a shorter shelf life and lacks sustainability

Decomposing peat moss contaminates stored potting soil with an overabundance of carbon dioxide. And in large quantities, releases CO₂ back into the environment. Contributing to a global greenhouse effect and the loss of critical wildlife.

Mixing in natural compost and other elements that improve fertility, drainage and aeration are far more effective and sustainable. 

Using Potting Soil That Smells Bad 

Our sense of smell is usually the first to tell us when something isn’t right. If your soil starts to take on the bouquet of rotten eggs, this means it’s been sitting damp for a while and microbes like bacteria have taken up residence. That aroma derives from bacteria waste. 

If all this makes you want to reach for the bleach, hold on. To date, there’s no evidence to suggest that simply smelling this is harmful to people. And smelly soil can actually be remedied by following the same soil rejuvenation steps that I have previously outlined above.   

How Long Does Potting Soil Last In Pots 

We know that nothing lasts forever. But, as long as your potting soil is producing healthy plants, it’s also being amended and maintained with every plant feeding and watering.

That being said, if you happen to live in a region with harsh winters and like me, you do a lot of garden clean-up in late September, you’ll need to do something with the soil that lived in your containers all summer. Rejuvenating this container-based potting soil means it can be reused over several summers providing you follow a few simple tips first.

  • In autumn, empty your pots and store soil in water-tight containers
  • In winter, store water-tight containers in a cool, dry place
  • In spring, rejuvenate your soil with fresh compost 

How Often Should You Change Potting Soil 

Potting soil used around garden annuals can be stored then rejuvenated. But, perennials can live in it until they outgrow the pot, then be offered new soil when re-potted.

The need to re-pot houseplants or add new soil will occur far more frequently as we tend to water and feed these more. Resulting in faster growth in certain varieties and a loss of soil (from frequent watering) in others. 

Replacing Soil In Pots 

To avoid root shock, repotting and soil replacement should almost always be done towards the end of the growing season, as plants are entering winter dormancy.

Your plant’s condition, at this time, will indicate any soil changes that need to be made. Have a good look at your plant before you report it and ask yourself: Is the plant healthy? Does the plant need a more nutrient-rich type of soil? Or maybe, better drainage? There’s no better time to make these adjustments than when you’re repotting or simply changing out old soil.  

How To Store Potting Soil Mix 

A potting soil mix that is stored in damp conditions will be subject to mold and bacteria growth. Resulting in either an unpleasant smell taking over your space or an accelerated decrease in soil quality. 

Storing soil the right way will give you clean, usable soil for many sunny seasons to come. While also saving you time and money. Here are a few options for you to consider:

Opened Soil

  • Store unused soil in original, resealable bag
  • Store soil in large plastic bins or tubs with tight sealing lids (Both new and re-purposed work great)

Unopened Bags of Soil

  • Store in a cool, dry place. Preferably up off the ground and out of direct exposure to sun, snow, insects and animals 

Storing Opened Bag Of Potting Soil 

It’s always a plus if new soil comes in a resealable bag. You can simply re-seal any you haven’t used and it’s ready for the next time you need it. If not, use your imagination and what you have to hand! I’ve used those oversized, resealable travel bags for clothes and even 2-gallon freezer bags for smaller amounts. 

More can easily be stored in large storage containers found at most discount stores. And if the space you store these things in is a little too damp, you can either store them off the ground or put the soil in those plastic, resealable bags first and then into the storage containers. This will create double the protection. 

Storing Bagged Potting Soil 

Opened or unopened bags of soil are best protected from wet winters and humid summers when fully sealed from moisture, mold spores, and bugs. Some can wiggle their way into the smallest of openings and find a place to lay their eggs.  That’s not fun when you go to open the bag again later. So, a tight seal is important.

Plastic containers are pretty crucial too because containers made of other materials like wood, metal, or ceramics just don’t create that same airtight effect. And if the bag inside breaks from soil weight, there’s no mess. 

Where To Store Potting Mix End Of Season 

One thing though, these containers are not impervious. If you live in a harsh winter region, storing these containers where they’re exposed to sub-zero temperatures will result in freezing and expanding soil and a cracked container. They’re best stored in a well-protected area. 

One exception is if you have oversized, outdoor pots filled with soil. It wouldn’t be practical to keep emptying and filling them. Provided they have adequate drainage, these can be left outside. They’ll fill up with winter rain and snow but will drain and dry out when spring returns.