Does Potting Soil Go Bad? (4 Important Signs to Look Out For)

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Last Updated on April 20, 2023

Potting soil is important to provide a growth medium, moisture, and nutrition for any growing plants.  There are different types and qualities of potting soil, and if you find good ones you may be tempted to buy a lot. The answer to the question, ‘does potting soil go bad’ is important to know if you plan to store it for long periods. To find out the answer to this question, keep reading.

Potting Soil Composition

Potting soil is a vital component of any garden. Unfortunately, it can go bad over time, rendering it unusable and unsuitable for plant growth.

Commercial potting soils usually contain peat moss as the primary ingredient. It can also contain other ingredients such as perlite, vermiculite, and pine bark. All these components have different functions;

  • Peat moss – a fibrous material that contains nitrogen and phosphorus which are nutrients required for plant growth
  • Perlite – helps with aeration, water retention, and drainage in the soil
  • Vermiculite – improves the nutrient content of the soil and water retention
  • Pine bark – improves moisture retention and aeration

A good potting soil should be able to hold water and nutrients that will be used by plants for growth. In some instances, it can even be enhanced with fertilizer or water-holding crystals which will help your plants to perform well. The ratio of the different components of potting soil can be varied and adjusted depending on the plants that will be grown in it

Potting soils are usually cheap, hence people can purchase large quantities at a time. They are also lightweight and easy to bag and sell.

It is different from the soil in your garden which is natural. Garden soil is made up of sand, silt, and clay, and can also contain organic matter particles such as those from leaves and grass clippings.

Old potting soil loses value over time as its ingredients, like peat moss, decompose faster than organic materials, hence potting soil loses its quality faster than regular garden soil.

Do you know what is the difference between Perlite vs Pumice and Which is The Better Soil Amendment?

How Long Does Potting Soil Last?

Potting soil can go bad – but it doesn’t happen overnight. The rate at which this happens depends on a few factors.

Open bags of new potting soil can stay for between 6 and 12 months without losing its quality. Unopened potting soil however stores even better and can last for up to a year or two before it goes bad.

Potting soil that is used to grow plants will usually go bad after about a year, or a single growing season. After this period, the soil will no longer be able to support the growth and health of plants and will either need to be replenished or replaced.

Read more about A Step By Step Guide On How To Sterilize Potting Soil

Facts about potting soil

How to Tell If Potting Soil Is Bad – The 4 Signs to Look Out For

You should be able to tell when potting soil has gone bad, here are the 4 important signs you should look for;

1. Off smell

If you notice a rotten egg smell coming from your potting soil, it may be because it has gone bad. This bad smell is caused by anaerobic bacteria and sometimes fungi that grow in old, damp, and compacted soils.

Putting your damp soil out in the hot sun may help to kill some of these bacteria and fungi that break down the soil. You have to be careful however because this can potentially destroy some of the nutrients that are in the potting soil. Some potting soils also have beneficial social microbes added to them, and the process of putting the soil in the sun can kill them. This would only be a concern for specialty potting soils, it is however something to keep in mind.

2. Insects and pests

Bugs and other types of insects are attracted to decaying organic matter. So if you see these infesting your potting soil, it is a sure sign that it is no longer in good condition.

The most common insects that infest rotting potting soil are fungus gnats. These feed on decomposing or decaying organic matter. They deplete nutrients in the soil and damage plant roots, and as a result, the soil will not be suitable for plant growth.

To deal with this issue, you can add diatomaceous earth to your potting soil and it will kill the bugs in there.

3. Mold development and growth

Mold grows on the top surface of the potting soil, especially when the soil has been exposed to damp or moist conditions for an extended period of time, without sufficient ventilation. The mold can be white, grey, yellow, or green in color, and can also have a fuzzy and slimy texture.

If you see mold growing on top of your potting soil, let it dry out in a place that has adequate aeration. Check the soil after a couple of days to see if it is still moldy.

Moldy potting soil can cause the roots of your plants to rot, and dampen off young seedlings if used.

4. Soil compaction

As potting soil breaks down in quality, it starts to form clumps. This is because of the decomposition of peat moss. The soil starts to compact and becomes dense. This then creates drainage and aeration problems and makes it difficult for roots to grow.

If you would like to continue to use the potting soil that is obviously breaking down in quality, you can add some goodness back into it by mixing in some organic matter such as compost or some more peat moss.

Does Potting Soil Expire?

Potting soil can lose its quality over time if it is not used and kept in unfavorable conditions. To keep it in good quality for longer periods of time, keep it in an airtight bag that is free from moisture, and away from sunlight.

Does Unused Potting Soil Go Bad?

Unused potting soil can go bad but it doesn’t happen overnight. Old potting soil loses value over time as its ingredients, like peat moss, decompose.

The range of time it takes potting soil to go bad is anywhere between 1-3 years. For unopened and unused potting soil, you can store it for about a year or two before it goes bad.

If unused potting soil has been stored in a shed or a garage and has come into contact with water, it is probably best to throw it away. Potting soil can go bad if not stored properly.  If it is still dry, however, it may still be viable for growing plants.

Problems With Using Decomposed Potting Soil

Decomposed potting soil not only looks and smells bad, but if used in that state it will cause various problems that will disrupt or even impede the growth and productivity of plants. Here are the 4 problems associated with using decomposed potting soil:

Reduced plant growth:

Decomposed potting soil contains much fewer nutrients than fresh potting soil. If it is used to grow plants, they will have stunted growth, weak leaves, and delayed flower and fruit development.

Compressed/compact potting soil:

The potting soil will compress or compact as the peat moss breaks down. It will pack around the roots, resulting in the impediment of water and oxygen flow. This will lead to eventual ill health and even the death of plants.

Reduces soil drainage:

The compaction of potting soil will disturb drainage. This will lead to water-logged conditions and the plant roots will not be able to breathe. Plants require well-drained soils to be able to grow efficiently and healthily. If a plant is placed in permanently soggy or water-logged soil, it will die.

Salts build-up:

Fertilizers and salts build in the soil. This becomes even worse if the soil has poor drainage. This build-up will eventually kill the plants, especially if the plants cannot withstand high salt concentrations. The fertilizer build-up will result in fertilizer burn on the plant leaves.

How to Revive Old Potting Soil for Plant Health

While using old or decomposed potting soil will do more harm than good to your plants, not all hope is lost as it is possible to revive the soil. Here are some of the options you have;

1. Repot plants every year:

Because potting soil usually lasts for a year or a single growing season, to give your plants the best chance of good growth and health, repot them every year and give them new potting soil

2. Improve the bagged potting soil:

To potting soil that is still in a bag but has been sitting for a long time, you can add a few handfuls of perlite or vermiculite to revive it. This will not keep the peat moss from breaking down but will help keep the soil aerated. You can also add a handful of compost or worm castings to give it a boost of nutrients.

3. Flush the soil monthly:

Flush the potting soil monthly with fresh water to remove or slow down the accumulation of fertilizer and salts in the soil. This will also help to remove the mineral deposits from tap water if you use it to irrigate.

4. Make your own potting soil:

To save yourself the trouble of having to deal with decomposed potting soil from a bag, you can make your own mix with more organic ingredients from the garden. you can make your own mix with compost, coir (an organic alternative to peat), worm castings, vermiculite, and other soil additives that you can find. This may seem like a lot of effort, but it is completely worth it and will last longer than commercial potting soil mixes.

How to Store Potting Soil

Potting soil can go bad if not stored properly, to make it last longer, you will need to know how to store it well.

Keep any unused potting soil completely dry. If it comes into contact with any moisture, it will start to develop mold and mildew which will damage the quality of the soil.

You can also store it in a plastic container with a watertight lid or an unscented plastic bag. Place it in a cool, dark place in a water-safe room.

For unopened and unused potting soil, you can store it for about a year or two before it goes bad, and opened bags will last 6-12 months.

Conclusion – Does Potting Soil Go Bad?

Potting soil is worn out because the peat moss has decomposed. If you want to continue to use the soil or want to give your plants the best chance at growth even after the first growing season, use the measures outlined above to replenish or replace the potting soil once every year.

Providing your plants with good quality or fresh potting soil or maintaining the quality of the soil that is already in use will result in your plants being much healthier and growing better.

If you notice or suspect that your potting soil is going bad, it is better to be safe than sorry for the sake of your plants. Do not use it, rather get fresh potting soil or make your own mix.

We hope this article provided you will all that you needed to know about potting soil going bad.

Happy growing!

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