I can’t tell you how many times I have bought bags of potting soil for some gardening project or another and left it in my shed for over a year. Usually, I get around to using it eventually, or I throw it into the compost when I need more soil.
Sometimes when I use it, I wonder if it is still potent so many months after I bought it. Is old potting soil still as useful for plants, and does it still contain healthy fertilizer?
All of this led me to investigate whether or not potting soil ever goes bad.
Does Potting Soil Go Bad?
Bad potting soil is a reality that many gardeners face. Most potting soil is only optimal for 12 months shelf life or so before there is degradation in the texture and quality of ingredients.
Potting soil can also go bad due to improper storage or contamination. Each of these issues can lead to problems for plants and soil conditions. Mold, lack of oxygen, and smells, as well as off-gassing of fertilizers, are just are few problems with old potting soil.
| Problem With Potting Soil | Common Causes | What to Do? |
| Loss of texture and soil structure | Organic material like peat moss decays faster than other soil and compost | Get soil from the compost pile and replace lost soil volume and improve the structure |
| Water-logged high-moisture potting mix | moist soil stored near water or in a humid environment accumulates excess moisture | Place the potting soil out in fresh air where it can dry out before storing it in a better location |
| Inert Soil Mixture | More than 12 months of storage can lead to loss of nutrient levels in organic fertilizers. | Add 20%-50% compost and other soil additives slow-release fertilizers will still be active |
| Fungus Gnats and Pests | Fungus gnats are attracted to moisture and water-logged soil | Use an organic pesticide and air out potting soil. Do not use infested potting on potted plants, or it may cause root rot. |
| Mold and Odors | Moisture and excess water cause mold and gnats | Toss the mold and potting mix in the compost, where it will be heated to kill spores. Gnats and their eggs will die too. |
- Loss of texture and soil structure – Soil bags from last year may not be the same as when you bought them due to their short shelf life. The texture and earthiness will change, and compaction may settle in. Some ingredients like peat moss will break down and cause compaction in the potting soil. Nutrients will also be lost, and organic materials such as peat moss will decay rapidly.
- Water-logged high-moisture potting mix – Soil can wick moisture out of the air and quickly become full of water-related issues. If a plant is put in potting soil that is wet, then root rot could result. Let the potting soil lose some moisture in the fresh air, or add it when gardening to a larger garden bed. Beware of mold and gnats in wet soil.
- Inert soil mixture – Plants need a lot of nutrients, and potting soil is the main way potted plants get them. The organic material in potting soil is usually a slow-release fertilizer that breaks down over time. If stored in ideal conditions, this could be 2 or more years, but fresh potting soil makes the best organic fertilizer.
- Fungus gnats and pests – Plants that are exposed to potting soil with fungus gnats can develop root rot and other moisture-related problems. Using insecticide spray with organic and plant-safe ingredients, try to kill the gnats in and around the potting soil. You can compost soil with gnat eggs and use the high temperatures and other ingredients in the mix to kill them.
- Mold and Odors – Storing unused soil near water can cause a build-up of moisture. Plants planted in this potting soil will be affected by mold and a soil environment that is not good for nutrient absorption. Mold can cause illness if inhaled and presents a plethora of problems for plant growth and healthy life in the soil.
How to Determine Potting Soils Expiration Date?
If you can’t immediately use potting soil in your outdoor garden, you will want to find a way to store it. Unlike compost which stays fresh for a long time, potting soil has ingredients that begin to break down and release fertilizer the minute it is mixed.
Without plant roots to absorb the nutrients and fertilizer in the soil, potting soil becomes less effective for future plant growth with every passing month. If the soil has been sitting in a warehouse for months before you even brought it home, then it will not have many nutrients for your plants.
You can determine potting soil’s expiration date in a few ways:
- Texture and Weight – Without opening a bag of potting soil, you can tell its freshness through your sense of touch. Fresh potting soil will be loose and have a lot of vermiculite and perlite chunks. Over time all of these components break down and compact. Fresh potting soil will also feel cool and moist through the bag.
- Smell – Fresh potting soil will have an earthy, petrichor aroma that is pleasant and musky. As the soil gets older, the smell will turn dusty, and the air will feel hot in your nostrils.
- Sound – If you move the soil around in the bag, you can hear how it tumbles. Fresh potting soil will fall in clumps and will hold longer before a large group tumbles. Older potting soil will sound more like sand or lose dirt moving through the bag. There will be little clumping and just a dry rustle of expired potting soil.
Signs Your Potting Soil Is Bad
When gardening in containers with potting soil, you will want to use fresh soil. Unwanted life-like gnats or garden pests that love moisture and mold can be attracted to bad potting soil. If you want to keep your gardening soil clean, look for these signs:
Moisture Problems
There are countless signs of moisture content problems in potting soil. Some of the most common are odor and pest problems. Fungus gnats are quick to infest wet potting soil.
The moisture allows the gnats to create life and reproduce in huge numbers. Gnats eat plant roots and the nutrients in the soil, making them nasty competitors for your garden plants.
White mold and noxious odors can also arise from potting soil with too much moisture in wet conditions. Mold will inhibit proper growth in plants and cause the product and soil to stink. Don’t use moldy potting soil in a clean container, as it will contaminate the pot. Clean storage containers that had mold potting soil in them well.
Structure Problems
Peat moss and other slow-release fertilizers break down in as little as a year. In improper storage conditions, that can happen even faster. Potting soil should appear light and have a fluffy texture. Products like coir and other natural solution can improve the structure and add nutrients, and fertilizer salts won’t break down as quickly as organic ones.
Nutrient Problems
Potting soil without microbial life or that has been stored for too long in poor conditions can lack nutrients. Sunlight exposure, open garden storage, and other bad environments for potting soil can further decrease nutrient and fertilizer capabilities. Damaged bags and opened products will degrade the most and have the fewest nutrients.
Ways to Store Potting Soil Effectively
Potting soil must be stored in good conditions in the right environment to preserve the ingredients and nutrients inside. Microbial life is common in potting soil as coir products help improve storage life. But creating the right environment is up to you.
Temperature
Potting soil should be stored in a cool area where nutrients in the fertilizer won’t break down. High temperatures can lead overactive bacteria and microbes to eat the nutrients meant for plants and reduce the effect in the garden.
Sunlight
The ingredients in potting soil can be volatile, and sunlight is a strong catalyst. Storing potting soil in sunlight can cause the ingredients to break down and will kill beneficial life in the mix. Lack of water can make the mix crumbly and unsuitable for plants.
Store all gardening soil out of direct sunlight. Like with compost, sunlight can be used to kill pests or remove excess water from the potting mix before gardening with it. Plants can still benefit from potting soil that has been exposed to sunlight if it hasn’t been blasted for too long.
Location
Water is a common enemy of potting soil. In a humid environment, the air can have more water than the potting soil needs. Excess water can cause problems, so potting soil should be stored in a condition of low humidity. Keep soil dry to keep soil healthy.
Heat and cold can affect some ingredients and microbial life in potting soil, and extreme temperatures on either side should be avoided. Plants and gardening soil need life in it, and if microbes are removed due to a poor storage location, more life can be added to the compost.
What to Do with Unused Potting Soil?
Old, expired, and unused potting soil can easily be revived using a few tips and tricks. When potting soil encounters issues that will make it useless to plants, you can pump it up with new ingredients, compost, and plant materials.
Plants need a lot of nutrients, and potting soils are designed to have what plants need. When plants can’t get these nutrients, supplements are needed. Compost is one of the best ways to add nutrients to your potting soil. Compost is made of food scraps and other biodegradable materials that are perfect for plants.
Plants also need soil with life in it. Microbes and bacteria help plants absorb nutrients and improve gardening success. Compost is also a great source of life and organisms that will help your plants eat all their food. Adding 20%-50% compost is a great place to start.
The structure of potting soil can deteriorate over time and cause compaction when gardening. Plants can’t grow well in compacted soil, and gardening zones with compaction will have drainage and water problems.
Adding compost is a good way to break up soil and give plants a break from the compacted dirt. Plants will take advantage of the loose compost soil to expand their roots and grow further. More compost can help add nutrients and make plants even healthier.