As a gardener, I’m always acquiring more ceramic planters for the garden. They’re great for adding color to areas where you can’t plant in the ground. But I was reminded this past winter that pottery can emerge from a hard freeze with cracks and breaks. (As someone with a legitimate degree in ceramics, I should have known better, but we all make mistakes.) If you live someplace that can experience a freeze, you should also take steps to protect your outdoor pottery during the cold months.
Clay, from which pottery is made, consists mostly of silica, other minerals, and water. If the clay is heated to the right temperature in a kiln, it is considered vitrified, where the silica converts to glass, all the water is gone, and the piece should be very strong. Most importantly, it won’t be able to absorb any water, which is important if you’re making, say, a vase. However, most pottery planters are made of terra cotta clay and are purposefully under-fired, so they’ll allow water to pass through, which is why those cheap red planters tend to break and crack easily. And sadly, even a lot of expensive large glazed ceramic pots are made in bulk and aren’t fired correctly to the right temperature. As a result, the clay can still absorb water. In cold enough weather, the water expands and freezes, and your pots break.
In the most ideal conditions, you bring your pots indoors for the winter. Store them in a garage, or shed. This includes your ceramic pots, garden tags or sculptures, and even your ollas, which are ceramic watering vessels that have become popular. Understandably, this is not always possible. You might not have space, or you might have plants in the pots that can’t sit inside all winter.
Use bricks or wood to raise your planters off the ground to allow water to drain more effectively, while hopefully hedging against some freezing. You can also insulate the planters by wrapping them in burlap or even bubble wrap. Every little bit helps.
It’s not just the planters themselves trapping water that is a problem. If your planter is full of soil, and that soil is wet, and then it freezes… you see where I’m going. One way to solve for the soil expansion is to fill part of the negative space in the pot with an empty water jug. The plastic jug will contract, making room for the frozen soil around it. This is a common method to fill space in planters anyways, since it means you need less volume of soil to till the piece, and you save some weight.
If you’re determined to leave your pottery outside (hey, me too), you could consider sealing the pottery to help prevent water from being absorbed into the clay. There are all kinds of spray, dip, and paint-on sealants for this purpose, and as long as you ensure that you’ve really covered every nook and cranny well, this should help prevent the pot from absorbing water, and thus cracking.
