Does Potting Soil Go Bad? When Does It Expire?

Potting soils are great for gardening and growing healthy plant roots, but the sizes of the bags generally means you end up with some leftover soil.

What do you do with the extra potting soil?

Often times, you roll the bag up and put it in the garage until next season. But this usually leads to you questioning if it’s still good when spring rolls around again.

does soil expire

So you might end up with old bags of potting soil in your garage, wondering if it’s still good, or if you need to buy new potting soil.

Does Potting Soil Go Bad?

Yes, potting soil does expire – but mainly because a common ingredient, peat moss, only has a lifespan of 1-2 years. 

If your potting soil doesn’t include peat moss, the answer isn’t as clear – check these other methods to see if your potting soil shelf life is over.

How to Tell if Your Potting Soil is Expired or Has Gone Bad

So you have a bag of soil and you’re wondering if it’s still good. Here are a few ways to help you decide.

1. Check the Expiration Date

Sure, this one seems obvious if you’re looking at food products, but did you know that your bagged potting soil should have an expiration date on it?

If you’ve forgotten which bag you bought 5 years ago and which you bought last summer, check this date. If it’s been more than 2 years since you’ve purchased it and it is expired, it might be time to throw it away or use it elsewhere (keep reading).

2. The Smell Test

Crack that baby open and let’s see what it smells like. Seriously. If you didn’t store the soil properly, fresh soil can end up becoming “bad potting soil.”

Because some of the ingredients just rot or can include mold, you’ll likely smell a rotten smell.

Rotten eggs, anyone??

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3. Mold

If you open the bag and it doesn’t smell weird, take a closer look. What does mold look like on potting soil?

It generally shows up as white speckles that are generally smaller than perlite or vermiculite.

This mold is called mycelium and generally comes from leaving your potting soil in a warm, wet area. When you expose the soil to the sun and fresh air, it should kill off most of this mold.

Buttt….if you’re like me, you’ll probably toss it because, moldy potting soil is gross. 🙂

4. Insects in the Bag

Fungus gnats are a common problem with potting soil – they are those pesky little black flies. Even if it’s not expired, these are common when buying new potting mix.

Just take a look at the Amazon reviews section of any potting soil brand:

Disgusting. But it’s true. Most potting soils retain excess moisture as some potting soil is left outside and rain gets in through holes, etc.

Fungus gnats can get into opened and unopened bags of soil through small holes. Then they lay eggs, and forget it – they’re everywhere.

You can try and get rid of them, or you can just get a bag of new potting soil.

I had this issue and I end up slicing the bag in half, and letting it dry out in the sun for a few hours. Fungus gnats thrive in moist environments that retain moisture, so if you dry it out, you can likely reuse potting soil that once was affected by them.

Can You Use Expired Potting Soil?

Of course you can.

Gardening is really a personal journey, and not everything will work the same for everyone. Often you just have to decide if you want to use expired potting mix.

Yes, potting soil does go bad but you can recondition it and bring it back to life.

If you’re going to use some of it, it might be okay to use on indoor plants or plants you won’t be eating.

What to Do With Bad Potting Soil?

You’ve decided that the soil is just not good anymore and may cause harm to plants you’re growing. What can you do with bad or use potting soil?

Add it to the Compost Bin

Gardening and compost often go hand-in-hand. A lot of gardeners love using compost in the garden because it’s full of great nutrient and organic matter that is great to mix in with potting soil and garden soil.

Compost is essentially a pile of organic material or kitchen scraps that break down and turn into “black gold” or really high nutrient soil for your garden beds. You just have to add water and aerate your compost regularly and it will decompose on its own.

Adding in unused potting soil will allow it to rejuvenate and mix with the natural organic matter that’s in your compost bin.

Add it to Worm Castings

Worm castings are like mini ant-farms, but with worms. You can add your old potting soil to these farms so you can reuse the soil.

worm castings

Typical Ingredients in Potting Soil and When They Expire

So we answered the “does potting soil go bad” question, but why does it go bad?

Here is a list of the common potting mix ingredients and their expiration dates. Potting mix generally contains peat moss, pine bark, perlite and vermiculite. Each of these serve different purposes and go bad at different times.

1. Peat Moss

Also known as sphagnum, this is included in potting mix as a method of retaining water. Peat moss is like a sponge and can hold 16-26 times it’s dry weight.

Peat starts decomposing right away, so it’s usually only good for 1-2 years after being packaged. This is the ingredient that drastically decreases the expiration timeframe of your potting soil.

2. Vermiculite

Vermiculite is like a type of rock, and creates more pathways for air to move around your potting soil. In short, it’s an aeration agent and helps keep your soil from becoming compacted and/or waterlogged which leads to root rot.

Vermiculite does not expire.

3. Perlite

Like vermiculite, perlite helps with the drainage of your plants and to prevent compaction and water logging.

Perlite does not expire.

4. Pine Bark

Pine bark helps provide a layer of moisture so your soil mix retains its water. It also helps insulate your plant from super cold weather.

Pine bark doesn’t expire, however when added to potting soil it’s often combined with pine bark extract, which can expire.

Does Miracle Grow Expire?

Miracle Grow is on a different level than potting soil – and honestly is something I’d never use. The weird color stuff they used to have makes me wonder, but a lot of people do use it.

The past owner of the house we just moved into left some in the garage and I’m kind of curious if it’s still good, or what I should be doing with it.

A lot of potting soil includes fertilizer added in, so does that expire?

If the bag is opened, it likely only lasts for a year maximum, as the slow-release fertilizer starts breaking down right away.

If the bag is not opened, AND is stored in a dry place, it should be good for around 5 years.

But, if it sat in a warehouse for a year before you bought it (which is something you wouldn’t know), I’d only use it for 1-2 years after purchase even if it wasn’t opened.

How Should Used Potting Soil be Stored?

If you’ve used potting soil during the spring, how can you make sure that it’s stored properly during the winter?

There are a few things to keep in mind:

  • Dry it out, and keep it dry
  • Keep it in the original bag
  • Put it in a storage tub with a lid
  • Store that tub in a dry place like your basement, shed, or garage

Potting soil is best stored in its original bag because they generally are resealable and they have the expiration date listed on the bag. If it’s resealable, make sure you reseal the bag, or use tape to seal the soil back up.

But make sure to keep it dry! Open bags of soil need to be dry before you put them back in sealed container, or else you’re going to end up with a mold problem and some bad potting soil.

Once it’s sealed, place the bag of old potting mix in a Rubbermaid or other storage tote with a lid. This helps keep it fresh and not exposed to the elements.

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