When you buy a bag of potting soil and keep it stored away for a while, does it go bad? That’s a common question I often get along with, “does potting soil have a shelf life?”
Or “how do you know when potting soil is bad?” If you’ve been wondering that, I’ll answer all the questions in this article.
Does potting soil go bad? Potting soil does not have an expiry date. But for the best quality, use an opened bag of potting mix within 6-12 months.
Beyond that date, the quality of the soil can change so you need to rejuvenate before using.
Unopened bags will last 1-2 years before the soil is affected.
However, there are also some instances where potting soil goes bad. Pests, bacteria, fungi and compacting are among the most common reasons that indicate potting soil is bad.
What is Potting Soil?
Potting soil is the kind of soil that is used for container plants. It differs from garden soil in that it is designed to keep plants healthy when they’re kept in small spaces.
In fact, potting soil may or may not be made of soil.
It is also worth mentioning that potting soil and potting mix are two different things, although most people will use the two terms interchangeably.
Potting soil may or may not contain soil. It is also heavier and will retain more moisture. As such, it is not always ideal for all houseplants especially those that are sensitive to overwatering.
That said, many houseplant do well with potting soil.
On the other hand, potting mix is soilless. That is, it does not contain traditional soil. instead, it uses ingredients that are combined to achieve specific functions.
This also means that potting mix is sterile so it won’t harbor any pathogens. And in many cases houseplant potting mixes are designed to be well-draining to avoid overwatering.
As such, potting soil is best used for gardening and landscaping outdoors.
In contrast, potting mixes are ideal for plants that are grown in pots, planters and containers.
For the purposes of this article, potting soil refers to potting mix since it is what most beginner growers and houseplant owners are used to.
Now that we’ve got that out of the way…
The reason why potting soil is very important especially for houseplants is that it allows the plant to breath, avoid overwatering and get nutrients. This gives your indoor plant the best chance to thrive.
Among the most important features of potting soil is its ingredients.
This can vary depending on the plant you want to grow. But in most cases, it will include components like peat moss, orchid bard, coconut coir, perlite, pumice, agricultural charcoal or sphagnum moss.
The purpose of these ingredients is to tailor the soil to a specific plant’s needs.
This allows the soil to hold as little or as much moisture depending on the plant you’re growing. And it also lets you customize how well the soil drains.
More importantly, if you’ve had the potting soil sitting the shed or somewhere for a while now, some of these ingredients may decompose or get compacted.
Thus, it can affect the overall function when mixed with other components.
So, the question is, does potting soil go bad? And how long can you store potting mix.
Finally, if it does deteriorate after some time, can you still use it.
I’ll be answering those questions below.
What Makes Good Potting Soil?
But first, lets delve into what makes good potting soil.
Note that not all potting soil is good. Some don’t work well while others are not well-suited for your specific plant.
Therefore, when considering the kind of soil you’re getting, also refer to your plant’s needs.
For example, a cactus or succulent will need a different kind of potting mix compared to an orchid. Aroids including philodendrons and monsteras also require different kinds of soil.
Therefore, you don’t want to just use the same kind of soil for all your houseplants.
That said, a good potting mix has the following features. And this makes it ideal for indoor plants.
When soil is lightweight, it means that it is not dense or compacted. Instead, there are tiny spaces between the particles.
This allows air to pass through and reach the roots.
Why is this important?
Because a plant’s roots needs both water and oxygen to stay healthy. The balance of the two is important otherwise the plant will eventually struggle.
Too much air means the roots are dried out. Therefore, your plant is at risk of dehydration which will cause wilting and brown crispy leaf tips and margins.
If left like this for extended periods of time, the plant will deteriorate because it needs water to perform its basic processes.
On the other hand, too much water means the roots are drowning in moisture. Thus, they cannot breathe or get any bit of oxygen in.
If this happens for an extended period of time or consistently, the roots will eventually suffocate, leaving your with root rot.
Therefore, lightweight soil is crucial to good root health.
In addition to air and water, it also allows the nutrients from fertilizer to get the roots.
Another aspect of good potting mix is drainage. Here, you’ll hear terms like well-draining and free draining to name a few.
Note that this does not meant that the soil will just drain liquid that you pour onto it. Instead, with potting mixes, good drainage or well-draining means two things:
- It holds moisture but not too much of it (just enough to keep the plant hydrated)
- It drains excess moisture
Thus, you get a balance of both.
This allows the plant to get their fill of water while getting rid of excess water. In doing so, it helps avoid waterlogging or overwatering where the roots end up sitting in water.
Plants need nutrients. And while some plants will do well without them, having nutrients in the soil will help it grow faster.
Therefore, one aspect of a good potting mix is nutrients. This is why you’ll hear some plants need rich potting soil or soil with lots of organic matter.
Both refer to nutrients that will help the plant grow optimally.
Here’s a chart that lists the different types of potting soil commonly available or used for houseplants.
Does Potting Soil Go Bad?
Yes and no.
Potting soil does not have expiry dates like other products do. Therefore, you technically can say “it does not go bad”.
Also, in most cases, potting soil that hasn’t been used does not go bad. Instead, its quality may change or not be optimal depending on the ingredients.
That said, if you have potting soil that’s been lying around for a while and does not look its best, you can still rejuvenate it with a bit or work.
Therefore, don’t immediately throw it out.
However, there are a few things that can make potting soil go bad. Here are some symptoms:
- It has a foul odor
- There are insects or pests in it
- It has been infected by some pathogen or disease
- The soil has become dense or compacted
These are all warning signs. And when you see them, don’t use the soil on your plants.
The good news is that you can still fix the soil. So, don’t just throw it away.
The key is not to use the soil because they can harm your plants in its current state. But after resolving the issues, they’ll be safe to use.
Meanwhile, if none of the problems above are present, then you can use the potting soil.
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How Long Can You Keep Potting Soil?
Potting soil is best used within 6 to 12 month after you’ve opened it.
Like most things, once air and moisture enters the sealed package they start take cause reactions. In the case of potting soil, you’ll notice it get compressed or compacted faster if the bag has been opened.
This is less of a problem with unopened bags of soil which will preserve the quality and consistency of the soil for 1-2 years.
That said, some ingredients can break down with time. One example is peat moss which will do so and compost actively.
This is likewise true for organic matter.
Similarly, nutrients in the soil, be it natural or added, will also deteriorate the longer they are unused. So, while the soil won’t be completely void of nutrients, don’t expect it to be as potent as it was when the soil was new.
Finally, there’s the risk of the elements. This depends on where you leave the soil.
If it gets wet by the rain or dries out under the very hot sun, the soil’s consistency, texture and function will change. Thus, try to keep it away from sunlight and in a dry place like your shed or garage.
How Do You Know if Potting Soil is Bad?
Above, I mentioned the warning signs to look out for that will tell you that potting soil is bad.
Now, it is time to take a more in depth look at each of these signs so you know why they can be harmful to your plant.
Just as importantly, how you can fix each issue to revive the soil for use.
Bad Smell / Foul Odor
Bad smell is never a good thing. And it is a tell-tale sign that potting soil is bad. In the case of potting soil, it will smell like rotten eggs.
This is caused by bacteria that has developed in the soil. In this case, it is anaerobic bacteria which means that it does not need oxygen to grow.
These pathogens grow in soil that is dense or compacted.
Therefore, by getting rid of the bacteria, the soil should be usable again (and will not smell).
To kill the bacteria, leave the soil under the sun. You’ll want to spread it out in a single layer so all the soil particles get light exposure.
The sun will kill the bacteria, it will also dry the soil. The latter helps because bacteria thrive and spread in moist, damp environments.
There are Pests or Insects
Pests and insects in your potting soil is another bad sign. While the soil has not technically gone bad, you never want to use soil that’s ridden with pests.
That’s because the pests will make their way to the plants that use the soil. And soon enough they will attack the plants starting from its roots and move to the stems and leaves.
Fungus gnats are notorious for this. And although they’re not as harmful as other pests, it is still not something you want infecting your plants.
Therefore, the solution here is to get rid of the pests in the soil. Once that’s done, you can use the soil for your plants.
One way to do this is to mix 1 part hydrogen peroxide with 4 parts water. Then soak the soil this the solution.
You want to get the adults, larvae and eggs. If any of them are left behind, the cycle will just start over and repeat. Therefore, you may need to repeat the process until all the pests are eliminated including the larvae and eggs.
Another option to using hydrogen peroxide is to use insecticidal soap. In this case, mix 1 teaspoon of Dr. Bronner’s liquid soap with 1 liter of water.
Again, soak the soil in this solution to get rid of the pests.
Make sure to let the soil drain and dry afterwards.
Mold Sets In
It there’s too much moisture where you stored the soil, it can cause mold to develop. This can happen if you’ve left the soil in the bag and kept it in warm weather.
To get rid of mold, follow the same steps with bacterial.
Spread the soil out under the sun and allow it to dry. The combination of the dry environment and the sunlight will kill the mold making it safe to use the soil for your plants.
It has Gotten Compacted and Dense
If soil has become dense and compacted, then you’ll need to rejuvenate it. I’ll go through the details in a section below.
How to Store & Keep Potting Soil Fresh
To keep potting soil fresh for as long as possible, it is important to store it properly.
For the most part, it is easier to store potting soil if you live somewhere with consistent temperature. This way, you can just store it away in a dry place from sunlight.
However, if you live somewhere with winters, it can be trickier.
The cold weather, damp conditions and lack of light in general increase the risk of pest, mold, fungi, and other pathogens.
From above, you know none of these things are good. And that they can make perfectly good soil go bad quickly.
So, here’s how to store away your soil so that you don’t end up with a nasty surprise.
For opened bags of soil, pour the soil into a container that is sealable or where you can tightly close the lid. Keep it away from moisture like rain as well as very hot or very cold conditions.
I like using dark colored container that is not transparent or translucent. This will keep light out.
Avoid leaving the soil in an unopened bag since insects and pests can easily get in. Also, any opening will either dry out the soil or cause it to get damp. Both are not good for your potting mix.
Unopened bags are easier to store away. Keep it in its sealed bag and put the entire bad in a container or a storage bag you have.
Always check the soil before storing and when you’re about to use it. You don’t want any plants, plant carts, sticks or anything else in the soil.
Can You Revive Old Potting Soil?
In most cases, yes.
But before you do, it is important to inspect the soil. Make sure to check for any bad smell, pests or disease.
If you find any of the problems fix them first before you rejuvenate the soil. That way you know the soil is safe to use.
It does not make sense to rejuvenate the soil if it harbors pests or pathogens that will ultimately damage your plant.
Can You Reuse Old Potting Soil?
Yes. However, you’ll notice some differences with the soil.
Like many consumable products you buy, you can use them even after you’ve kept them for some time. But you may notice some differences.
With soil there are 3 noticeable things different old from new potting soil.
- Nutrient content
- Ability to hold or drain moisture
But that does not mean you cannot use old potting soil.
Since each of the factors (and all of them together) play a role in your plants’ health and growth, it will ultimately affect how your plant grows and behaves.
That said, you can make adjustments to supplement or remedy these issues.
For example, the longer you keep potting soil, the less the nutrient content will be. As such, old soil won’t have as much potency as new soil does in terms of the mineral content.
However, you can add compost to the soil or use fertilizer to fix the issue.
Similarly, if you notice that that the old soil is not draining moisture as well as if it were new, you can add perlite, pumice or bark to improve drainage.
As such, don’t throw away old soil since you can use it to grow healthy plants.
Instead, monitor how your plant reacts to the soil and make any adjustments if necessary.
How to Revive/Rejuvenate Old Potting Soil
If you want to use old potting soil, it is a good idea to revive the soil and give it a boost before growing your plants in it.
That’s because when soil is left in storage, it becomes susceptible to the elements. And depending on whether the bag has been opened or not, it can change the composition, texture and other aspects of the soil.
Therefore, here are some ways to revive or rejuvenate old soil before you use it.
If the soil has gotten compacted, dense or heavy, add coconut coir. You can use peat moss as well although coco coir is more eco-friendly. Additionally, it also lasts longer so you don’t need to replace it after a year.
If you decide to order your coco coir online, it is a good idea to get them in dry bricks. This will make shipping a lot cheaper since they’ll be lighter without the moisture. You can get a big bag of it.
Rehydrate the coco coir bricks before using (the product will have instructions). Then combine 1 part of your potting soil with 1 part of the coconut coir.
If your soil has been sitting around, its nutrient content will have deteriorated. Therefore, it is a good idea to add organic matter to the soil. You can do so by adding compost, worm castings or organic fertilizer.
Note that different plants need varying amounts of nutrients. Therefore, it is a good idea to tailor the soil to the need to the specific plant you want to grow in it.
If you’re not sure what the nutrient content of the soil is, you can use a home soil test kit. Then amend the soil based on your plant’s requirements.
Ways You Can Reuse Old Potting Soil
I know some growers who don’t want to spend the time rejuvenate old soil. Instead, they’ll go out and get new soil. Then use the old soil for something else.
And you can do that as well.
Here are some ways you can reuse old potting soil if you don’t want to revive it and use it on your plants.
Use it as potting soil for your outdoor garden
While old potting mix may not be ideal for container plants, it will help your garden soil. Therefore, you can mix it in.
The old potting soil will add more volume and some organic matter to your garden helping your outdoor plants grow.
Therefore, while the old soil may not be ideal for sustaining plants on its own in a container, it can supplement and improve your garden soil.
Include it with your compost
Instead of throwing old potting soil away, you can use it with compost. Mixing it with the other ingredients will let you use the compost to improve other soil.
This way you don’t waste the old potting soil and put it to good use.
Put it in your worm bin
If you have a worm bin, you can likewise use the old soil there. This way you can eventually use it to add organic matter to your plants to reduce the need for fertilizer.