How Long Can You Use Old Potting Soil For?
Essential to gardening and houseplant lovers alike, potting soil is a necessary component of growing plants in pots. Just as you take care of your plants, you also need to take care of your soil.
When repotting your plants or emptying a pot, you don’t have to – or need to – dump the soil out in the bin. You can keep hold of it and use it again!
Potting soil can be reused year after year with proper care and revitalization. After being used for a year in one pot, you can move it into another and recharge it with some compost and a bit of mixing. You can even use potting soil for two years in a row!
Just make sure you properly sterilize your old potting soil by baking it in the sun or using boiling water. You don’t want to grow bacteria or pests as well as plants!
Can you reuse potting soil?
As long as it isn’t infested with pests, growing mold or the plant in it wasn’t diseased, you can reuse potting soil easily.
Depending on how long it has been stored or sat in a pot, you should check how healthy it is and revitalize the soil as needed. Old potting soil will be depleted of nutrients, which means any plants grown using that soil might not grow to their full potential.
It’s a good idea to introduce more nutrients into used potting soil anyway, as plants pull nutrients from the soil as they grow and thrive.
Reusing potting soil is a great way of cutting down on your gardening costs, especially if you have your own compost heap or access to the community compost. It also cuts down on plastic packaging, as many gardening supplies – especially soil, compost, and manure – are packaged in unrecyclable plastics.
You can reuse your potting soil for vegetables, flowers, houseplants, or anything else. If using it for any plants that you might eat from, always make sure to sterilize the soil even if it looks healthy and the plants previously seemed okay. You don’t want to accidentally introduce disease into your edible plants!
If you’re into vermicomposting, you can reuse your potting soil in your vermicompost bins, as worms can suppress plant diseases found in the soil.
To store your potting soil for later reuse, make sure you have a storage container that is fully sealed and water-proof. A tight lid is essential – you don’t want any pests getting inside and laying eggs inside!
Make sure the potting soil is dry before closing the lid on it, because trapped moisture could result in the growth of mold. Then put the container in a well-ventilated area that will stay dry.
When can’t you reuse potting soil?
You should be careful when reusing old soil in case it contains any bacteria, fungi, viruses, pathogens, or larvae. This can increase the likelihood of your plants becoming diseased or dying.
Old potting soil also contains fewer nutrients, which can weaken the plants that grow in it or even prevent them from growing fully.
Do I need to change potting soil every year?
Most potting soils, especially any made with peat moss, are designed to last for one year or one growing season. After a year, the soil begins to compact down, which prevents the soil from draining as well. The amount of nutrients in the soil is also reduced.
That doesn’t mean you have to change it! There are a number of ways to help rejuvenate old potting soil.
How often should you replace potting soil?
It depends on what plants you’re growing, as well as how you care for the soil and the plants. You should aim to check on the soil and replenish it as needed once a year.
Can you save potting soil for next year?
Old soil can be stored to use later, but always make sure to sterilize the soil before you reuse it. Over time, pests could be introduced to the soil while it’s stored away, so sterilizing the potting soil will ensure you don’t introduce any pests or diseases to new plants.
Should you remove old soil when repotting?
Removing old soil when repotting is good for the health of your plants, because old soil will be depleted of valuable nutrients. You can always store your potting soil to reuse next time you repot, or add it to a compost heap.
How do you know if potting soil is bad?
The most obvious signs that it has gone bad include:
- A bad smell (like rotten eggs)
- Presence of insects
Potting soil which has a dusty green, yellow, or white layer on top of it has mold. This is most common with soil that is soggy or saturated with too much water. Mold can cause root rot in plants, so make sure to get rid of the mold as soon as possible.
Storing mold-infested soil in the sun and leaving it outside for some time can help kill off the mold. A natural fungicide will help deal with any mold spores too.
Mold can also indicate that you’re not taking proper care of your plants, so make sure to:
- Avoid overwatering plants – check what each plant requires
- Keep plants in sunlight – open curtains regularly and allow the sun in
- Check water is draining properly
- Keep your home well-ventilated
- Remove debris from the soil – put it in your compost heap instead
Bad smells, like the smell of rotten eggs, coming from your potting soil indicate that your soil is too compacted. If you have experience with bokashi composting or vermicomposting, you might recognize the smell.
The presence of insects should be dealt with quickly, as most of these will be pests that are attracted to bad soil conditions like rotting.
If a white crust forms on the surface of the soil, that means too much salt has been introduced to the soil. The salt buildup usually comes from the use of tap water.
Rainwater is better for potting soil because it contains less salt. Try to collect rainwater over time by placing a bucket, watering can, or rainwater storage tank.
Is dried-out potting soil still good?
Old, dry potting soil without any sign of mold, bad smells, or pests should still be good to use! However, it will be depleted of nutrients, so revitalizing your old soil should be your first step before introducing it to a pot.
How do you revitalize and reuse potting soil?
First, let it dry out so it’s easier to transport. You can set it aside after moving your plants into a different container or store it in a wheelbarrow or bin.
Storing potting soil over winter is good practice, so you can bring planters inside if they’re in danger of cracking in freezing temperatures.
Once the soil has been dried out, remove old stringy roots and branches. You can add them to your compost heap.
While roots and branches will decompose over time, they take longer to decompose than leaves and other parts of plants. Leave any old leaves in the potting soil so they can decompose in the soil and return any nutrients into it.
It’s ideal to dry out the potting soil over winter because the best time to pasteurize the soil is once it starts getting hotter in spring.
Pasteurizing is a form of partial sterilization and uses heat. The process will kill off any pests or bacteria. Solarization is an eco-friendly method of pasteurizing your potting soil and is ideal for large amounts. Boiling water can also be used to pasteurize soil.
However, solarization does require the use of plastic to cover and hold your potting soil. You can use old plastic bags or packaging though! You can also reuse plastic tarpaulin.
Lay a layer of plastic on the ground or fill a plastic bag with the potting soil. You want a thin layer of soil to sit on the ground, so pat down the soil until it’s only a few inches high. Make sure the soil is covered by plastic – transparent is best. Set the bag or soil in direct sunlight and let it sit.
Make sure to:
- Secure the plastic sheet or bag with some stones or planters so it doesn’t blow away, try to make sure all open edges are weighed down
- Break up any lumps in the soil so it can heat better
- Moisten the soil a bit by watering it or spraying water onto the top of the soil until damp – don’t overwater though
Solarization can take around four to six weeks to fully pasteurize the potting soil, so it’s worth setting it out as soon as you can and leaving it.
Once you feel the soil has had enough time to pasteurize, remove it from the bag and mix it with fresh potting soil or compost.
A 50/50 mix of old and new potting soil works well but you should add some more nutrients to it – small chopped-up pieces of vegetable waste, sprinkling compost, or worm castings can help introduce fresh nutrients. Mix well so there’s no layer difference between old and new potting soil.
If you have compost instead of fresh potting soil, add 1 part of compost to 5 parts of soil and mix it well together. You can also add worm castings to this mix for extra nutrients.
Slow-release fertilizers can also be beneficial, but make sure to find certified organic fertilizers that don’t use synthetic chemicals!
How do you recharge potting soil?
For potting soil stored in containers or planters, you can recharge the soil by turning it with a cultivator and adding compost. Make sure to mix it well together so the nutrients go throughout the soil and water can still drain well.
How do you sterilize potting soil?
There are five ways of sterilizing potting soil:
- Boiling water
Potting soil is sterilized at temperatures of around 180°F.
The first method is to use solarization, as described above, by heating the soil under the sun using plastic. This does come with the risk of introducing microplastics to the potting soil.
The second method is steaming, which requires a steamer pot with a suspended pot inside it. By bringing the water to a boil, the steam penetrates the soil and drains up through it.
Boiling water is one of the easiest and most eco-friendly methods. After putting the potting soil in a bucket or heat-resistant container, fill up a kettle halfway and boil the water, then carefully pour the hot water into the soil until the soil is moist (but not saturated). Turn the soil until it begins to clump and then let it cool.
Microwaving can work for small amounts of old potting soil. Make sure that the soil is slightly moist and mixed, and put it in a lidded microwave-safe container with ventilation holes. Put the container inside, preheat to 200°F, and cook the soil for 30 seconds after steam appears. The soil should be in the microwave for between 1 to 5 minutes.
Turntables are essential when using a microwave for sterilization, otherwise, the soil won’t be completely sterilized all the way through.
Sterilizing potting soil in an oven is the final method and one you might want to avoid if you struggle with strong smells. Like the microwave, your oven should be preheated to 200°F.
The soil should be put in an oven-safe baking dish and mixed well, with water to moisten it but not saturate it. Let the soil remain loose, not compacted. Then wrap aluminum foil around the dish.
You’ll need a thermometer in the center of the dish poking out of the foil so you can see the temperature. Put the dish in the oven and wait for the temperature to reach 160–180°F, then leave it in for at least 30 minutes before removing the dish. Let it sit until it’s cooled down.