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.
And what do you do with the extra potting soil?
Oftentimes, you roll the bag up and put it in the garage until the next season. But this usually leads to you questioning if your potting soil is still good when spring rolls around again.
Does Potting Soil Go Bad?
Yes, potting soil does go bad – 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 might not be as clear – check these other methods to see if your potting soil shelf life is over.
How to Tell if Your Potting Mix 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??
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 anything 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 a 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 ended 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.
What to do if New Soil Smells Moldy?
If you can, take it back to the store. But if the return timeframe has passed, you can slice the bag open and let it dry out in the sun.
This should remove the moisture in the bag and get rid of the smell. From there, you can store the soil in a plastic container.
If you don’t want to use that poor soil, you can add it to your compost bin and it will break down well in there.
Can You Use Expired 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 it 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 the plants you’re growing. What can you do with bad or use potting soil?
Add it to the Compost Pile
Gardening and compost often go hand-in-hand. A lot of gardeners love using compost in the garden because it’s full of great nutrients 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 good 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.
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 soil generally contains peat moss, pine bark, perlite, and vermiculite. Each of these serves different purposes and each goes bad at different times.
1. Peat Moss
Also known as sphagnum peat moss, this is included in potting mix as a method of retaining water. Peat moss is like a sponge and can hold 16-26 times its dry weight.
Does Peat Moss Expire?
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.
Vermiculite is a type of volcanic 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.
Does Vermiculite Expire?
Vermiculite does not expire as it’s simply a type of rock.
Vermiculite does not expire.
Like vermiculite, perlite helps with the drainage of your plants and prevents compaction and waterlogging.
Does Perlite Expire?
Similar to vermiculite, 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.
How to Store Potting Soil
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 plastic storage bin 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.
If you can’t reseal the bag, I would move the soil to an airtight container with a lid.
Either way, make sure to keep it dry! Open bags of soil (or loose soil) need to be dry before you put them back in a 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.
Frequently Asked Questions About Potting Soil Going Bad
Does Potting Soil Go Bad if it Freezes?
Potting soil can’t freeze unless it has some kind of moisture in it. If you stored a wet bag of soil and it freezes, you will end up with a block of ice, but once it thaws it should be perfectly fine to use in the garden.
This is why it’s important to make sure your soil is completely dry before storage.
Does Opened Potting Soil Go Bad?
An opened bag of potting soil is fine to use as long as it’s not expired (check expiration, and follow the steps above to make sure). However, if you left an open bag of potting soil open all winter (as in, not folded over the top or put it in an airtight container) it might be time to get some new soil.
Is Dried Out Potting Soil Still Good?
If your potting soil is truly dried out and not retaining water any longer, that might be an issue. But that doesn’t mean you need to completely get rid of it unless it’s compacted soil.
In most cases, you can simply add compost to the soil to incorporate nutrients back into the soil. You can also incorporate the ingredients of Mel’s mix, which is my favorite soil combination for raised beds, potted plants, and containers.
When plants are growing, they pull nutrients from the soil to help themselves grow big and produce for you, so old soil is likely going to have some sort of nutrient deficiencies, especially if you’re growing in containers that can’t pull nutrients from the ground.
How Long is Potting Soil Good For?
Potting soil is usually good for between 6-12 months after opening. After that point, it will have begun breaking down and lose effectiveness.
Seed starting mix won’t lose nutrients, as there aren’t any in there, to begin with, but it can lose its ability to hold or drain water.
Does Miracle Gro Expire?
Miracle-Gro 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.
What to Do With Old Potting Soil?
There are a number of ways you can reuse old potting soil. You can add it to your compost bin, and let that break down with other scraps and organic material. You can also amend the soil and reuse it for another season by adding compost and slow-release fertilizers.
While most potting soil won’t “go bad”, if you find moldy potting soil or it just smells awful, it’s likely a good time to toss it and start fresh with another batch.