The porosity of terracotta serves a worthy garden purpose by allowing water to evaporate out of the soil and air to infiltrate and cool the roots. However, it also is the very thing that makes them vulnerable to freezing winter temperatures, as moisture in the clay expands and causes the pot to crack. Not all terracotta pots are created equal, and there are steps you can take to protect them from sure destruction.
Types of Terracotta Pots
Terracotta pots differ by the type of clay they are made from and the temperature at which they are fired.
- Frost-resistant pots are a step up from the low-priced everyday terracotta pots. They are fired at higher temperatures, making them less porous. They are safe for areas with light frosts.
- Frostproof pots are best for areas with harsh winters. These pots are first allowed to dry naturally. They are then fired for 12 to 18 hours at very high temperatures and cooled slowly for 24 hours, creating a pot that does not allow water infiltration. Frostproof pots usually carry a 10-year guarantee against winter damage.
- Salt-glaze pots are fired at temperatures so high that it bonds the clay molecules together so that it is completely waterproof. These are the most sturdy frostproof pots on the market, although they can be expensive.
Sealing Terracotta Pots
Older terracotta is more porous than frost-resistant and frostproof types. To save them from cracking during a winter freeze, they need to be sealed to keep the water from penetrating the clay. Cheaper new terracotta pots can also be sealed with a mixture of water and polyvinyl acetate (PVA) glue. PVA glue is also known as wood glue, school glue, white glue or carpenter’s glue. To seal your pots, make a 10:1 mixture of water to PVA glue in a container large enough to submerge your pots. Obviously, this is a method better suited for smaller pots. Dip the pot into the solution for 30 seconds. Put it onto a rack to drain and allow it to stand overnight to dry. For extra protection, you can also add a layer of exterior varnish over the glue sealant.
Move Your Terracotta Pots
If you have no other choice, the best way to protect your pots from winter damage is to empty out the soil and move them to a warmer, drier location such as a garage. If you must leave them outdoors, choose a sheltered location next to the house and raise them off the ground to prevent water from wicking in from the soil. Wrapping or covering them with protective plastic or bubble wrap can also help if there is no other way to protect them.
Terracotta pots are an investment that give a beautiful and natural look to your container garden; however, winter can be hard on them. Planting in frost-resistant and frostproof pots is best, but you can also seal your older and cheaper pots or shelter them for added protection. Talk to your local pottery supplier for additional information on winter-proofing your outdoor pots. To find terracotta pots that will withstand winter temperatures, visit a garden center such as Bob Williams Nursery Inc.