If you’re passionate about houseplants and keep potted plants in every strategic corner of your house, then potting soil must be a staple of your gardening passion.
You would think that potting soil, being just soil, would never go bad or at least have a long shelf life, but that couldn’t be further from the truth.
How long does potting soil last? Potting soil degrades over time and eventually goes bad. On average, the expected shelf life of an open bag of potting soil is about 6 months. That number could dwindle considerably if you don’t store it properly. Unopened bags can keep the potting soil in good condition for one to two years.
So how do you keep your potted soil stored properly? Would the potting soil in an unopened bag go bad? Read on to find answers to these questions.
Potting Soil Shelf Life
The shelf life of the potting soil depends on how you store it and whether you’re using it or not.
For unused soil, humidity and poor storage conditions can degrade the soil rather quickly. The organic matter in the potting mix combined with humidity and poor ventilation lead to the buildup of mold.
Does Potting Soil Go Bad?
Potting soil tends to go bad if left unused for a long time. The main ingredient in the potting soil, peat moss, tends to degrade.
The chemical structure of the soil changes, and before you can use it again, you’ll need to rejuvenate it and cure it.
Does Potting Soil Have an Expiration Date?
A bag of potting soil usually has an expiration date. You should use the potting mix within that expiration date.
Otherwise, the potting mix loses its natural drainage properties and becomes easily water-logged.
The pH of the expired potting soil also changes, rendering it unusable for the plants you bought it for.
How Long Is Unopened Potting Soil Good For?
Potting soil comes in tightly sealed bags that insulate it from humidity and fungus spores.
If you keep the bag in a well-ventilated and dry place, the potting soil inside is good to use for up to 2 years. Any cracks in the packaging would reduce the shelf life of the potting soil drastically.
How Long Does Potting Soil Last Once Opened?
Once opened, your potting soil has a shelf life of no more than 6 months. Again, this is the average shelf life in ideal conditions.
Peat moss tends to degrade quickly in humid conditions. If the potting soil gets contaminated with fungal spores, mold could build on the soil.
Can Used Potting Soil Be Used Again?
You can reuse potting soil as long as it’s not contaminated with bacteria from a diseased plant. This also depends on how long the used potting soil has been in the pots.
If it’s relatively fresh soil with only a few months of use, then you can reuse it again, but if the soil has been in the pot for a year or more, then you should fill the pot with fresh soil.
Should Potting Soil Be Replaced Each Year?
The rule of thumb regarding potted plants is to freshen up the potting soil once a year, unless the plants are slow to grow and will not deplete the soil quickly.
In that case, you can replace the potting soil about once every couple of years. To freshen up the soil, add slow-release organic materials, mix it well to improve drainage, and stir the soil to oxygenate it.
Does Potting Soil Go Bad if It Freezes?
Freezing potting soil doesn’t make it go bad. It can be an effective way to sterilize the soil.
If the soil gets contaminated with pathogens, fungus spores, or tiny pests, then placing the bag in the freezer for a few days can kill these pesky pathogens.
Allow the frozen potting soil time to thaw, then mix it with organic materials before using it in pots.
Is Dried Out Potting Soil Still Good?
You can still put dried-out potting soil to good use. As long as the soil has enough nutrients in it, you can rehydrate it and use it for growing plants.
To rehydrate dried-out soil, place it in a shallow tray filled with water. It might take the soil a couple of hours to absorb the water.
Once rehydrated, work in some compost or slow-release fertilizer (this one is excellent) to replenish the dried-out organic materials.
How To Tell If Potting Soil Has Gone Bad
When the peat moss in the potting soil degrades or decomposes due to high levels of humidity and poor ventilation, it changes both in color and smell.
You might notice a green or yellow powdery material on the surface of the potting soil. That’s mold buildup.
The other telltale sign that your potting soil has gone bad is when it reeks of a smell like rotten eggs.
Insects crawling all over the potting soil is a sure sign that the potting soil is no longer usable. The bugs are attracted to the decomposing peat moss, so you have to throw it away.
How To Store Potting Soil
While bags of potting soil are often sealed tight, if you want to store it for more than a few months, then you should place it in a plastic bin and close it firmly.
Some potting soil bags are resealable, which allows you to open them, take as much soil as you need, and reseal them.
If the bag is not resealable, then seal the bag with duct tape and place it in an air-tight container. Keep the container in a well-ventilated and dry place.
How To Rejuvenate Old Potting Soil
If you leave potting soil unused for months on end, it will become old, lose its nutrients, and become useless in pots.
To rejuvenate this old soil, you’ll need to spread it on a tarp under the sun. Add water to the soil to flush out any excess salts. Let the soil dry, then mix in fresh soil at a 1:1 ratio.
Test the soil’s pH (this 3-in-1 meter tests pH as well as moisture and light levels) to make sure it’s around 6.5. Finally, add slow-release fertilizer, and let the soil cure for about 2 weeks.
What To Do With Old Soil?
If the old soil is not contaminated with bacteria or pests such as fungus gnats, then you can put it to good use by throwing it in the compost bin.
The old roots in the soil will decompose nicely and enrich the compost.
Does Potting Soil Need To Be Sterilized?
Even fresh potting soil in unopened bags can contain pathogens.
To be on the safe side when potting seedlings and cuttings as well as sowing seeds, it’s recommended to sterilize the potting soil first.
Microwaving moist potting soil is the best way to sterilize it and kill all pests and pathogens in it.
Potting soil is packed with organic materials that have a short shelf life. Peat moss in the potting soil is good for one or two years if the potting soil bag is not opened.
However, other factors, like dampness, can accelerate the decomposition of these organic materials, rendering the potting soil useless.