Not all flower pots are suitable for year-round outdoor use - generally, only "high-fired" pots are able to survive the temperature changes and the freeze/thaw cycle. Examples of pots that don't make this cut are most Mexican terra cotta planters, and most Italian red clay pottery. Also, any pots or vases that do not have drainage holes should be brought inside.
Once you’ve determined that you have a flower pot that will most likely survive the worst that winter has to offer, it’s important to note that it’s generally not OK to just leave the pots in the same condition that they were in during the growing season.
Obviously, the best option is to bring your ceramic flower pots inside, or to at least cover them with a tarp. If those aren’t options for your containers, or if you really like the way the pots look, and you want to keep looking at them all winter, there are lots of things you can do to ensure that your beautiful pots continue to look great and last through the winter:
Keep the Drainage Holes Open – Hands down, this is the single most important factor in determining if your planters are going to make it through the winter. Do NOT plug up the drainage holes in any way on pots that you intend to leave outside through the winter. Please note that this does NOT mean that the pots need to be totally empty, but if you pour water into the pot, it should start dripping through the drainage holes within minutes. This is best accomplished by placing a layer of small rocks, broken pots, Styrofoam peanuts, or similarly-sized materials on the bottom of the pot, which will prevent the drain from getting blocked with soil clots. Ideally, this layer will be about 10-15% of the interior height of the pot. See the photo at bottom left for an example of a pot properly prepared for winter use.
Use A Potting Soil Blend that Allows for Drainage – You should be doing this anyway, but if you aren’t, Fall is a great time to change out your potting soil. Again, the goal here is to make sure that water can drain fully to the bottom of the flower pot.
No Saucers – Seriously. Saucers do a lot of great things – they help to keep your plants hydrated through the hot seasons, they protect your decks and floors, and they look great with many flower pots. They are also your flower pots’ worst enemy during a deep freeze. Any residual water left in a saucer when the cold hits will freeze. This will not only cause the saucer to become stuck to the planter, but it can also pressure the foot of the pot, causing breakage or crumbling. The ice-filled saucer will also plug the drainage holes on the bottom of your pot, allowing the pot to retain water, and in turn presenting the opportunity for ice to expand and break the pot from the inside out.
Use Pot Feet – Again, there are a lot of reasons for doing this. First, using pot feet keeps the bottom of the pot elevated, which enhances drainage. This elevation also keeps water from pooling below the pot, eliminating the risk of the pot freezing to the ground.
Don’t Light Fires in Your Pots – Cold ceramic planter + burning logs = broken planter. 100% of the time. Get a fire pit.