Does Potting Soil Go Bad? Tips For Reinvigorating Old Soil

Does Potting Soil Go Bad

I am not sure if it’s just me or if this is something that everyone does, but I buy things and then forget about them for weeks, months, or even years at a time.  It is especially true if it is something I plan on using further down the line. 

I have more than a few bags of potting soil at the back of my garage that’s been sitting there since we bought our house, which was 5 years ago at the time of writing this article. 

Which brings us onto the question, does potting soil go bad? Potting soil will not go bad if it’s stored in the correct manner.  Like anything else that contains organic matter, potting soil can spoil or become infested with pests if it is kept in poor conditions.  

Luckily for us, potting soil can last almost indefinitely, as long as we care for it carefully.  Even if it loses some of its potency, we can rejuvenate and bring it back to its former glory with relative ease. 

If you want to learn more, read the rest of the article to find out how best to store potting compost, how to fix it when things go wrong, and how to supercharge old potting soil to make it better than new. 

What Makes a Great Potting Soil

The perfect soil has certain characteristics that make it what it is:

Lightweight: it needs to be light enough to not become compacted when wet or compressed.  Pots take up a small volume of space and will contain plant roots, so a soil that compacts too much can suffocate a plant or keep the roots too wet. 

Drains:  We want our potting soil to be able to retain moisture, but not too much.  The perfect potting soil will allow water to drain easily while retaining enough water for plants needs. 

Nutrients: All plants require nutrients to grow, and potting soil is no different.  Ideally we’d like our potting soil to slowly release nutrients for the plant to use.  Most commercially available potting soils will contain added slow-release nutrients.

What Should You Avoid

While it might be tempting to use garden soil as a potting mix, it’s rarely a great choice.  We cover the exact reasons why in this article, but in summary, it’s heavy and may contain a variety of unwanted pests and weeds. 

Store-Bought Potting Soil

Potting soils can be bought from any garden center or online, and will last indefinitely if it remains unopened or if store correctly.  I’ve had a ton of great success with this potting soil, it’s got every great characteristic we talked about above. 

If buying a premade and premixed potting soil is not your thing, then you can easily make your own.  In fact, it offers several advantages:

  • You can tailor it to the plants your growing
  • It’s cheaper in the long run
  • You know exactly where ingredients come from
  • It gives you a good understanding as to the composition of potting mixes

I use a rather simple recipe, so feel free to elaborate on it and put your own twist on it.  My mix consists of one part Vermiculite, one part Perlite and four parts Mushroom Compost. 

The Vermiculite provides excellent water retention capabilities, while the Perlite provides excellent drainage and keeps the mix lightweight.  And finally, the Mushroom Compost provides a rich organic supply of nutrients, water retention and ideal structure for roots to flourish.  Additionally, Mushroom Compost is sustainable and has minimal impact on the environment. 

I have this mix that will provide plenty of nutrients for plants as they start out, but as the plants grow and mature, you will need to supplement their nutrient requirements.  One of the best ways of doing this is with slow-release organic fertilizer granules, I like these

If you have your own worm farm at home, which is something I recommend everyone to have if you garden, then you can use your worms castings and worm wee for supplemental nutrients. 

If you’ve made your own potting mix in bulk, you don’t need to throw it away at the end of the growing season.  Store it in a strong rubble sack, rubber maid or other container that will stop it from getting wet and stop any unwanted pests from getting into it.  Then simply leave it alone.  There’s absolutely no reason why it wouldn’t last years like this. 

How to Properly Store Potting Soil

Most potting soils can be stored for years without going bad with very little intervention, but to maximize your chances of success there are few steps you can take to optimize the experience. 

Make sure your potting soil is being stored in a suitable container.  Rubble sacks, rubber maids or strong storage containers work well as they keep out moisture and other unwanted contaminants. 

However, if none of these are available, at least try and keep your potting soil dry.

If you’re planning on reusing and recycling used potting soil, try and remove as much as the old plant matter as possible, including roots.  This just removed the amount of organic material available to rot.  Feel free to add this old plant matter to your compost heap.

Avoid keep old potting soil in pots outside over winter.  Chances are it’ll be absolutely fine, but if you have wet soil and freezing conditions, you might significantly reduce the life expectancy of your pots, especially if they are ceramic.  Frozen and frozen soil will expand, enlarging any existing faults in your pots. 

If your potting soil is wet, do as much as you can to dry it out before storing it for long periods of time.  This will reduce the amount of microbes that are present and able to break the potting soil down further. 

How to Reinvigorate Old Potting Soil

So, you’ve just come across a few bags of old potting soil at the back of your garage and you’re wondering if you can just go ahead and use or if needs something added to give I some oomph? 

Chances are it won’t need anything added, depending on how old it really is.  Potting soil that is months to a couple of years old will work just fine.  Older potting soil may have lost some of nutrition’s, but only slightly. 

The best approach for really old potting is to simply mix it with new at a 50 / 50 ratio.  

The next thing you’re going to want to do is to hydrate it again.  If you’ve store correctly, your old potting soil should be bone dry, so you’re going to want to wet it before use. 

I find the easiest and best way to do this is by emptying the potting soil into a wheelbarrow and gradually adding water until you can wring out a few drops of water with every handful. 

If you’ve added too much water, simply add more potting soil until the perfect consistency is reached. 

Your potting soil should now be good to go now, it’s rehydrated and in as good as new condition.  However, if you’re recycling already used potting soil, you’ll want to add some sort of fertilizer to enrich the nutrient profile.  Use whatever method your most comfortable with, we’ve listed several options above. 

What Else Can You Do With Old Potting Soil

If you have old potting soil that you don’t want to use in the next season, then there are multiple things you can do with it that will benefit your garden for years to come.

One of the easiest way to utilize old potting soil is to use it as a mulch.  Time will add structure and valuable nutrients back into the soil.  You don’t need to dig it in or anything else like that, just spread it around in your beds.

Mulch not only improves your soil but it also prevents water evaporation and provides some defense against weed growth. 

My favorite thing to do with old potting soil, or any other organic waste, is to add it to my compost heap.  Potting soil is full of microbes that will assist with the composting process, allowing other organic material to break down faster.  If you haven’t already started a compost heap, then starting one is one of the most valuable things you can do for your garden. 

If you don’t have a compost heap or don’t have room for one, then consider a worm farm.  They have a small footprint and you can add old potting mix to them, just not a lot at a time. 

With a worm farm, you can recycle most of your kitchen waste and turn it into some of the best organic fertilizers available, all for free!

Lastly, you can always give your old potting soil to someone else.  There’s always someone starting out with gardening without much of a budget, and some free potting soil might be exactly what they are looking for. 

FAQ

What if Potting Soil is moldy?  Like any organic material, potting soil can become moldy.  This is rarely anything to worry about and you can likely still use your potting soil.  The only time I would advise against it if was a black slimy mold with a bad smell. 

How many times can I reuse potting soil?  You can reuse potting soil as much as you want if it’s not full of roots and plant material.  You may need to add some fertilizer to really get benefit out of it.

What Happens If Potting Soil is Contaminated with Seeds? If you know your old potting soil has seeds in it, your best course is to add it to a compost heap.  A well-managed compost heap should get hot enough to kill off most seeds.