Reading Time: 10 minutes 🍃
Potting soil is one of the most important components for your garden, helping to provide nutrients to your growing plants. Because it’s so important, you’ll want to make sure that you are always using the highest-quality soil. So, will potting soil go bad?
The potting mix never really expires. But it will lose its nutrients over time. This makes it more prone to compaction. If you have an open bag, this degradation will take six months to a year. A sealed bag might be able to last for one to two years.
This is a complex topic. How long it takes the potting soil to lose its nutrients can vary. Plus, the lifespan of potting soil isn’t fixed. There are some ways that you can extend its lifespan. Keep reading to learn more about how you can care for your potting soil.
Can Potting Soil Expire?
Potting soil doesn’t expire. You will still be able to use old potting soil in your garden. But it won’t provide any benefits to the plants. This degradation of potting soil can be explained by the active ingredients that comprise it.
Potting soil is comprised of a range of nutrients. This includes things like peat moss. Over time, this will decompose. When in the garden, this is how the plants access the nutrients. In the bag, though, there is nothing to absorb the nutrients, so they become wasted.
While it might not have the same nutrients, old potting soil isn’t completely useless. There are a few elements that won’t expire, including
- Vermiculite. This is a type of rock. In the garden, it’s designed to help aerate the soil, so the plants can breathe.
- Perlite. This is a type of volcanic rock. It exists to provide drainage, stopping the soil from becoming waterlogged.
- Bark. This is used to retain moisture within the soil.
It should be noted that the minerals will still be degrading, even if the bag is left sealed. However, as long as the rest of the soil is in good condition, you might be able to salvage it. You can add some nutrients to the soil. A good way to do this is by sprinkling some slow-release nutrients through the mix.
Signs Your Potting Soil Has Gone Bad
Nutrients, like peat moss, won’t last forever. But, while it might be past its prime, old potting soil hasn’t necessarily gone bad. As we mentioned, you can add some slow-release fertilizers to return nutrients to the soil.
However, not all types of potting soil can be saved. Here are some of the warning signs that your potting mix might have gone bad:
- Bad smell. This is one of the easiest signs to spot. When you open the bag, you might be met by an unpleasant smell, resembling rotting eggs. This is a sign that bacteria have infected the potting soil. In this condition, there is a risk that your plants could get sick.
- Insects laying eggs in the soil. This is especially common amongst fungal gnats. If you use this soil, these insects will eat the roots of your plants. This will stunt growth.
- Mold. This is most common when the bag is wet. Mold spores will be attracted to these kinds of conditions. Once in the soil, the mold can spread quickly, until the whole bag has become affected.
- Compacted soil. This occurs because peat moss has broken down. Peat is known for its high moisture content. Without it, the soil can dry out quickly. If the soil becomes too dense, it won’t allow water to pass through it.
Reviving Bad Potting Soil
Just because you have bad potting soil doesn’t mean that it needs to go to waste. There are a few ways that you can bring this bad soil back, making it useable in your garden.
However, this will only work if you catch the problem early on. This will stop it from becoming a major problem. Here are some of the things you can try:
- Spreading it out in the sun. This can be a to kill the bacteria in the soil. It might take a few hours, but your soil should stop stinking.
- Put it in the oven. Another way to kill bacteria is by exposing them to high temperatures. Because of this, you might want to try spreading it across a tray and sticking it into the oven.
- Using sticky traps. If you have insects in the soil, you might be able to reduce their population size. In particular, you should consider using yellow sticky traps. These will prove to be particularly attractive to fungus gnats.
- Spray with insecticide. Another way to get rid of insects is by spraying the soil. If you are planning on growing food, it’s best to use an organic spray. This ensures that you won’t be exposed to any nasty chemicals.
- Break it up. If the soil has become too compact, you can try breaking it apart.
- Mix in perlite. This mineral is known for being high in nutrients. It’s also a good way of adding more moisture to the soil.
- Add worm castings. Another good way of infusing nutrients into the soil is through the use of worm castings. Plus, it will add a little more moisture.
It should be noted that these solutions aren’t perfect. Sometimes, they can introduce their own set of problems. For example, when you are sunning the soil, you will be killing any positive microbes. You will need to add these into the soil yourself. But, once you do that, the potting soil should be able to support plants.
Risks of Using this Soil
While it might seem like you have solved the problem, there aren’t any guarantees. There are a few things that can happen if you are using this soil. Some of the potential problems to look out for include:
- Compaction. Without the peat moss in the soil, it can become dry. When this happens, it can clump together into a hard layer. This will stop the water from getting through the roots.
- Salt accumulation. This is linked to the compaction of the soil. When this happens, there is the risk that fertilizing your plants will lead to the build-up of salt. This can poison the roots.
If you see this happening, there are a few ways you can try to solve this problem. For example, you might want to try flushing it out. Use a lot of water and allow it to flow out of the bottom of the pot. This should flush a lot of the salts out with it. However, it will put a lot of pressure on the roots.
How Long Does Potting Soil Last?
How long you will be able to store potting soil is linked to how quickly peat moss breaks down. This is the main ingredient in the soil and is one of the biggest reasons why it goes bad.
Sometimes, you might find that your potting soil has a best-before date on it. This gives you clear guidelines on when you should use the soil. If not, you will need to judge the condition of the soil yourself. You can feel it between your fingers. It should feel moist rather than dry. You don’t want to see signs of mold or clumping.
How fast it will degrade will often depend on how the bag has been stored. Ideally, the bag will be unopened. This will limit the amount of moisture that can enter the soil. As a result, the peat will last longer. It might be able to keep for around one to two years
.
Once the bag has been opened, you should try to use the potting soil as quickly as possible. In this condition, it will only keep for around six months. Sometimes, it might be able to keep a little longer. Some types of potting soil may still be useable a year after the bag was opened.
Ways to Keep Potting Soil Fresh
The good news is that the speed at which the soil degrades isn’t set. The environment that you store it in has a big effect on how long it will last.
The first thing you need to do is make sure that you are leaving it in a dry place. If the soil gets wet, it becomes an attractive habitat for insects and mold. You don’t just need to worry about the rain; you also need to think about the amount of moisture in the air. This can be measured using a hygrometer. You should make sure that it’s dry before you put it away.
If you have only used part of the bag, you should place it into a container rather than leaving it in the bag. Ideally, this will be an airtight container. This will slow the aging process. Make sure that you clean this before you put any soil inside it.
Don’t forget to label the outside of your container. The NPK and pH levels can change between different types of soil. Some people like to keep the label, reminding them of the type of soil it is.
There are a few other things you should think about when storing your potting soil:
- Keep it away from direct sunlight. This can break down the beneficial microbes in the soil.
- Remove any old plants or seeds. If you have been working with an open bag in the garden, some of the detritus likely ended up in the bag. But, if you store it for a few weeks, there is a risk that one of these seeds might germinate in your potting soil.
- Cooler environments are better. You don’t need to be worried about this element. But it’s generally best to put the potting soil in a cool place.
What to Do With Old Potting Soil
In many cases, you will be able to revive old potting soil. But sometimes, they won’t work. But that doesn’t mean that you should just throw it away. Here are some of the ways that you can put it to use:
- Add it to compost. If you have a lot of old soil, you can add it to the compost over a few months. When you do this, the worms will help to break it up. They’ll also infuse it with nutrients. Over time, this compost can be turned into a great source of food for your garden.
- Building a worm farm. This is one of the best ways to get nutrients into your garden while breaking down your kitchen scraps. The old potting soil can be the basis of your worm farm. These are easy to build. All you need to do is add plenty of water and cover with newspaper. Then, you’re ready to put the worms in.
- Dealing with erosion. You might have parts of your property that have been affected by erosion. This is especially common after periods of heavy rainfall. You can use this soil to fill any of these areas.
What to do With Used Potting Soil?
Sometimes, you might have had a successful growing season with the potting soil. But now the plants have died off, and it’s time to give the soil a new life. There are a few ways that you can refresh this old soil and get it ready to be used again.
- Remove the roots. This is the first thing that you should do. Make sure to give them a good shake to remove any loose dirt.
- Flush the soil. This is a good way to lower the salt content in the soil, which can creep higher through the use of fertilizers.
- Leave it in the sun to dry. This serves two functions. It ensures that the soil is completely dry before you put it away. It also kills insects and mold spores.
- Sterilize the soil. If you do discover signs of bacteria or insects, you will need to take a few extra preventative steps. One of the most important is a process known as solarization. This involves putting the soil into a black bin. Seal the lid tightly. Then leave it in the sun for the day. It should get fairly hot; this will kill off any bacteria or insects in the soil.
- ‘Bake’ the soil. Another way to sterilize the soil is to put it into the oven. It will only take half an hour for the bacteria to be killed. If you prefer, you will be able to put it into a covered container and stick it in the microwave. Don’t forget to put in air holes. It will only take 30 seconds to be sterilized.
When you are ready to use the old soil, you will need to mix it with a newer potting mix. This ensures that your plants are getting plenty of nutrients. It’s good to use 50-50 mix while adding in some slow-release fertilizers.
When Can’t Potting Soil be Reused?
There are a few times when you might want to think twice before you use the potting soil. One of the best examples of this is when there are signs of insect activity in the soil. As we mentioned above, there are some ways that you can get rid of these pests. You can lay the soil in the sunlight or use insect traps.
But there is still a risk that you might have missed some. Adding plants into this environment risks the whole garden being infected. Instead, it might be best to add it to compost. This will allow the worms to break it down.
If you see signs that the soil is infected, you should take action immediately. Put the affected plants into quarantine. This will stop it from spreading to the rest of your garden.
How Much Potting Soil Do You Need?
A lot of the issues associated with potting soil going back can be caused by purchasing too much. But how much will you need to pick up when you visit the hardware store? This will often depend on the size of the pot you intend to fill. Here is a general guide:
| Pot size | Number of quarts of soil |
| 8 inches | 3 |
| 12 inches | 12 |
| 16 inches | 22 |
| 24 inches | 24 |
These calculations can often prove to be a little difficult. This is a useful online calculator you can use to help you out. All you need to do is plug in the dimensions of the container you plan on using, and you’ll get the amount of potting soil you’ll require.
It’s also important to remember that you might have some rejuvenated old soil that you will be able to use. This reduces the amount of new potting soil that you will require.
Final Thoughts
Potting soil has a best-before date. After this point, it will start to lose its nutritional value and will be more at risk of compaction. You might be able to extend how long it lasts by changing the way you store it. After it’s past its prime, you will need to do some remedial work, like adding slow-release fertilizer, before you can start using it in your garden.
Sources
- https://bovees.com/does-potting-soil-go-bad/
- https://www.homefortheharvest.com/how-to-store-potting-soil/
- https://modernfarmer.com/2013/05/how-to-build-a-worm-farm/
- https://www.lovethegarden.com/au-en/calculator/potting-mix
