Unopened potting soil has an expiry date as a guideline; opened bags last for around 6-months before degradation begins.
Bad soil lacks moisture, dries up, and any micro-organisms break down until they have no nutritional value for the plants.
To increase the life span of opened soil, tape the bag closed and place it in a sealed tub. Store it in a cool, dry place, where extreme heat or cold can't cause further degradation.
How to Tell if Potting Soil Has Gone Bad
There are 3-primary signs that the soil's quality is compromised: Smell, Insects, and Mold.
1. Smell
If there is a sulfur, rotten egg smell as you open the bag, there is too much moisture in the soil.
You can attempt to dry out the soil by spreading it out in the sunshine to kill the bacteria; others mix in activated charcoal.
Most gardeners prefer not to risk their seedlings in smelly soil for fear of root rot.
2. Insects
There are microscopic organisms in all soil; it is to be expected, and they help keep it healthy.
Fungus gnats, Mandeville larvae, and whiteflies are different matter. They are tiny but visible creatures that want to drain the soil of all the necessary nutrients essential to plant growth.
Fungus gnats feed on rotting matter in potting soil. Their larvae are destructive and damage new roots, but, as adults, they have little effect on plants.
3. Mold
If the soil has a white powdery coating and smells damp, it has mold infestation. Using this soil will cause root rot and result in little if any growth.
There are methods to repair the soil, including spreading it out in warm, well-ventilated conditions.
For the sake of a few dollars, we recommend disposing of any degraded potting soil and buying another bag.
What to Do With Expired Potting Soil?
Expired potting soil has many uses. For instance, throw it onto your compost heap; it can only benefit it by adding extra organic matter and volume.
Another option is to start a worm bin. Vermicomposting is making natural fertilizer with kitchen and garden scraps using worms.
It is a fast way to make super-rich, nutrient-dense food for everything that grows in your yard.
Add expired potting soil to your flower beds. The plants will benefit from the extra nutrients as long as you leave them to mix naturally over time.
Never be tempted to add soil from the ground to potting soil; it is 20x heavier and retains too much water; you will waterlog plants and end up with root rot.
Is Potting Soil Reusable?
When the time comes to plant out your new flowers, you might wonder what to do with the remaining potting soil and if it is reusable.
The soil is good for a couple of years, but not without some work to revitalize it and replenish lost nutrients.
- Remove any twigs, root balls, and dead plant matter.
- Use a trowel to fluff the soil and break down any clumps.
- Add nutrients; 1:1 compost to soil works, otherwise use organic plant food.
- Mix well and use.
If the soil is coming to the end of its second season, assume most of the nutrients are depleted and add it to the compost heap or flower beds.
Increasing the Life Span of Potting Soil
If you have a compost pile, mix it with potting soil in equal measure. The resulting compound retains moisture by making the soil more porous.
The compost slowly releases additional micro-nutrients to feed the plants.
It is a natural, eco-friendly way of aiding plant growth without harming the environment.
Should you Sterilize Potting Soil?
Sterilizing soil is the practice of removing harmful bugs and their larvae from the mixture.
It relies on odd methods that include baking, microwaving, or adding boiling water to the soil.
The best and safest way to sterilize soil is to use the heat from the sun, but only attempt if there is a problem.
Sterilizing new potting soil before use is a waste of time and effort; it is made from sterile ingredients. Heating it to temperatures high enough to kill eggs would prove detrimental; it also kills the healthy micro-organisms beneficial to the soil and plants.
In point, it would make good potting soil go bad.
