The quick answer? Keep it somewhere dry, but let’s go into more detail, so you know exactly what should and shouldn’t be done when you’ve got excess potting soil come winter.
You wouldn’t be the first to have overestimated how much potting soil you need to get your houseplants and contained segments of your garden thriving and colorful from May through September. It’s best to get too much than too little and have to make multiple trips to the garden center, right?
You’ve saved on fuel, saved carbon emissions, saved money by buying in bulk, and for a few floriferous months, your garden and windowsills were brimming with delightful colors and sweet fragrances.
But now the skies have taken on a steely hue and slowly but surely crawl their way across the once blue sky, bringing rain, blocking sun…the frosts on their way. What are you to do with all the potting soil you have left?
Well, first thing’s first; don’t throw it away. There’s life in the soil yet, or…there will be once you plant some amazing flora in it. Throwing it away on account of the season may seem like a no-hassle solution, but keeping it safe and sound through the winter months doesn’t take all that much effort.
The key thing to remember in this soil scenario is that the cold isn’t an issue. That’s right, fellow green thumbs; come frosts, come snow, come the next ice age, your soil is safe. No matter how cold your soil gets in the winter, it’ll still be rich and fertile when the sun returns for some summery goodness.
In fact, your potting soil is better off in the frosty sways of winter than it is in any other season. “Surely not”, you say. “But why?” you ask. The reason you shouldn’t give a hoot about your soil surviving the snows is that the frosty temperatures keep insect life well away.
While a small amount of insects doesn’t pose a massive risk to your potted plants, if they multiply and infestations become more severe, their creeping and crawling can cause root damage.
Perhaps more to the point, regarding your indoor plants, your home is your sanctuary, and the last thing you want is to make it a halfway house for wayward bugs.
If you’re already dealing with an indoor bug infestation, don’t worry about it. Critters like fungus gnats are a common hitchhiker when it comes to bringing some greenery and/or flowers into your home.
You can get rid of them in a number of ways, but I’ve had success in the past using a combination of this BioAdvanced Insecticide Fungicide to oust the creepers, and these Sticky Fruit Fly Traps to catch the flyers.
So, why is it exactly that the cold weather protects your potting soil from an insectile invasion? Well, the simple answer is that most insects HATE the cold. In many cases, winter is still a life and death situation for humans, but for insects, it’s a truly brutal time of year.
We mammals have the benefit of being our own furnaces. We generate body heat, especially when we huddle together like penguins or hunker down under a nice, cozy blanket.
Insects don’t have the luxury of being able to generate heat metabolically and so have developed two distinct strategies of wintry survival: freeze avoidance and freeze tolerance.
Freeze avoidance refers in part to migration, so we don’t have to worry about those particular bugs. For lack of better words…they’re someone else’s problem now — sorry, not sorry.
The prime example of a migrating insect is the Monarch butterfly. They travel from Canada all the way southward to Mexico and southern California.
The bugs we do need to worry about are the ones that survive by alternative means of freeze avoidance and the ones that live by the freeze tolerance ethos. These bugs are all about standing their ground and wintering at home, home being our gardens.
They have some intelligent biological processes to help deal with the cold, but for the most part, finding warmer shelter is their best bet. If we keep our soil resembling a block of brown ice, they won’t consider it a suitable shelter.
Keeping your potting soil dry, on the other hand, is a must, as saturated soil doesn’t have enough air pockets for you little green children to breathe, and it will inevitably lead to plant rot.
Can I leave potting soil outside in the winter?
Yes, you can absolutely leave your potting soil outside over the winter. As explained above, a frozen sack of potting soil is better than a warm one for keeping bugs at bay.
That said, you may want to pay more attention to protecting the bag than the soil itself, the reason being, if the bag is compromised, then the soil is compromised. Holes caused by extreme weather let in the rain, spill soil everywhere, and act as a giant, luminous “VACANCIES” sign for insects.
As potting soil is so dry, even tiny perforations in your sack can lead to a lot of water being siphoned in and spread throughout the contents.
Once it’s in there, with no sun to work its magic and dry it up, that moisture is going to stagnate, increasing the chance of fungal infection, and destroying those valuable air pockets our plants love so much.
This doesn’t mean you have to welcome your leftover potting soil into your home. You might just have to get a little bit creative with winter storage.
A popular solution is to do away with the bags altogether, emptying the soil into large bins with lids — any old wheelie bin will be perfect for the job. Standard garbage cans will also work a treat.
Another effective solution to the soil sack problem is to simply switch out the bag you bought your soil in for something more heavy-duty. Something like these ToughBag 55-Gallon Trash Bags might be just the muscle you need to keep your outside potting soil dry and insect-free during the winter.