Whether your planter boxes can withstand freezing temperatures without cracking depends primarily on the material they are made from and their construction. Not all planters are created equal when it comes to cold weather resilience.
Porous materials like terracotta and ceramic are highly susceptible to freeze-thaw damage. Water absorbs into these materials, expands when it freezes, and can cause cracks or spalling. Concrete planters can also be vulnerable for similar reasons, though high-quality mixes with proper curing fare better.
The most reliable choices for freeze-proof performance are durable plastics (like polypropylene or polyethylene), fiberglass, metal (if properly coated to prevent rust), and treated wood. These materials are non-porous or flexible enough to handle expansion. Proper drainage is also critical; trapped water at the bottom is a primary cause of damage.
To protect vulnerable planters, you can take preventative steps. Before winter, empty the soil, clean, and store them indoors. If they must stay outside, elevate them off cold surfaces, ensure drainage holes are clear, and consider wrapping them in insulating bubble wrap or burlap. Applying a sealant can also help waterproof porous pots.
In summary, while no material is 100% guaranteed, selecting planters designed for all-weather use and employing protective measures will greatly increase their chances of surviving winter unscathed.