Growing plants, whether indoors or outdoors, requires top-notch soil to help the plants take root and to thrive for many months to come. Plants are like babies in that they need the proper environment and nutrients to grow at the rate that they are meant to and to lead a long and healthy life. Potting soil is crucial to the success of any plant and can make or break the process.
So, one question many gardeners or aspiring gardeners ask themselves is, “does potting soil go bad?” Does it have a shelf life and, if so, how are you able to tell good potting soil from bad potting soil? Also, does the type of soil make a difference in if and when the soil turns sour? The short answer is, no, potting soil technically does not expire, however, the quality over time does diminish.
All of the above questions will be answered in further detail in this article, but first, let’s explore what potting soil is, what type of gardening it is used for and what ingredients make up good quality soil.
What makes up potting soil?
Potting soil is a very specific type of soil that is made for plants that will be confined to a small space and need added nutrients and proper texture to allow the plant to breathe. Potting soil may be used in outdoor gardens as well but it is not necessary for those plants to grow properly as they are in a more open environment with natural drainage and direct sunlight.
Many potting soils are made up of various ingredients to maintain proper texture, moisture and provide adequate nutrients to the plant that it is used with. One of the main ingredients that many top-quality potting soils contains is something known as peat moss.
Peat moss is great at holding moisture and contains many nutrients that are vital to healthy plant growth. However, if you have an open bag of peat moss-based soil sitting in a bag in your shed for a few months to a year and it has gotten wet, most likely that peat moss has decomposed.
This does not mean that the soil is completely unusable, however, it will not be the most ideal soil for proper growth for potted plants and they may not be able to sustain life in that soil. This soil should still be suitable for larger gardens.
A few other ingredients that are common in potting soil are bark and pearlite. Pearlite looks like tiny white pellets and are added to soil to keep it from getting too dense and not allowing water and air to properly circulate through the soil and to the roots of the plant.
The key to any good potting soil is that it does not compact too easily and it remains lightweight so it allows for proper circulation, as stated before, but also proper drainage so as to not drown the roots.
There are four different main types of potting soil that can be used on potted plants, all-purpose, premium, professional, and plant-specific. All-purpose potting soil is probably the most common for the average gardener.
It is a premixed soil that is great for potting new houseplants or repotting old plants that need larger containers. Premium and professional potting soils may contain things such as time-release fertilizer to feed plants for several months to promote strong root development but can be a bit more expensive. Plant-specific potting soil is just that, plant specific. Plants such as cacti and succulents need a different set of nutrients and more adequate drainage to thrive and grow to maturity.
As you can see, all potting soils general makeup is about the same but there are a few different ingredients here and there that you need to pay attention to when growing an indoor, potted plant.
So, does potting soil go bad?
Earlier in this article, I stated that potting soil does not necessarily have a shelf life, but it can lose its texture, moisture content and nutrient levels over time if not stored properly. So, it does not become completely unusable but the growing results may not be as good as they would have been with fresher soil.
All potting soils contain organic matter that, given enough time, will inevitably break down leading to a dustier consistency and can become denser.
Denser soil means there will be less ability for water and nutrients to circulate throughout the pot and gain access to the roots. It also means there will be less drainage happening and can lead to drowning the roots of your plants.
Now, it is worth mentioning that the time it takes for the organic matter to begin breaking down is highlight dependent on where and the way in which you store your soil.
Whether the bag is opened, unopened, sitting in direct sunlight, sitting in a damp environment or in a place where it can get rained on are all factors that affect the quality of your potting soil over time.
Opened bags of potting soil usually hold their highest quality for around 6 months to a year. Things like air and excessive moisture can reach the soil inside and begin to break down the nutrients and compress the soil at a faster rate than soil that is unopened for months before use.
The soil in an opened bag will not be rendered completely unusable and can be used for general use in your garden but potted plants certainly won’t receive the same benefits as they would have from fresher soil.
Unopened bags of soil will maintain their quality for much longer periods, keeping their value for about a year or two without being used. However, things like peat moss and other organic material are always actively breaking down even if you never open the bag.
There are some rare instances when your potting soil goes completely bad and should not be used on plants. You can tell if this is the case if you detect a rotten smell, see mold growing in the soil or have an abundance of gnats flying in and around the bag. This soil is the exception and should not be used on any plants.
All is not lost, however, if you have an open bag of potting soil or you have a bag you purchased, stored and then promptly forgot about. There are some methods and tricks you can try to make your soil last the longest that it can or revamp older or used soil.
Tips on Keeping Soil Fresh
As stated above, there a few ways that you can try to revamp old potting soil or to maintain your newly purchased soil if you won’t be using it right away. The first method is to mix in a couple of handfuls of perlite.
If you’ll remember from the beginning of this article, perlite is the little white pellets found in most potting soils that keeps it from getting too dense. Adding some more into the soil yourself could help slow down the decomposing process of peat-based soils. Adding some compost could help with this as well.
Another way to keep potting soil healthy is to flush it monthly when it is already potted with a plant. Take the plant outside or place it in the sink and run water from the tap or a hose directly into the pot.
Let all the water drain out from the bottom of the pot before placing it back in its growing area. This helps to flush out the fertilizer salts or mineral deposits from tap water that have accumulated in the soil.
Proper storage of potting soil can also make a huge difference in how long your soil maintains its nutrient and moisture levels. Over wintertime, for example, it is recommended to store used potting soil in a fresh and clean container such as a washed-out trash can or a new trash bag.
It is also important to let the old potting soil completely dry out from previous watering’s before you store it. For unopened bags of soil, you can simply place the bag in the storage container and place in a dry location.
As you can gather from the information above, the question of whether potting soil goes bad or not is not as black and white as we would like. Potting soil certainly does lose its potency and freshness, like any other product.
However, unless it is stored improperly and becomes completely rotten, potting soil that is older or used can either be revamped or used in a garden for general purposes. So, don’t throw out that potting soil that’s been sitting in your garage for months just yet!
Save yourself some time and money by taking proper care of your potting soil and utilizing it in other ways once the organic matter that is present has, for the most part, broken down.
Have you reused old potting soil or salvaged old and unused soil? Let me know in the comments! And as always, happy gardening!