First things first: What is double potting? The answer: The practice of placing a planted pot inside a larger pot.
Why would you do this? As all of us who live in Mohave County know, we have both hot summers and cold winters. Using a double pot method on your plants could help them survive both the hot and cold periods.
Unlike our feet, the plants cannot take their shoes off nor put socks on. The problem most people have with outdoor potted plants is that their roots become too hot and cannot absorb sufficient water and nutrients during the summer, and they get too cold (freeze) during the winter. The plant's roots are part of its main survival structure. Double potting gives them a better than 50 percent chance of survival during extreme heat and cold, assuming they are cared for and appropriate for our climate.
If you have a potted plant in an 8-inch pot, simply place it into a larger pot at least two inches larger in diameter (10 inches) and the same height or less. If you have a pretty decorative pot you want to use, but it's too tall, just lay in some empty plastic bottles or other material in the bottom until desired height is reached. You could add rock, but that makes for a heavy pot.
Fill the two inch or larger air space between the pots with anything you have available - old towels, newspaper, packing peanuts, Styrofoam, rugs, sweats, mulch or potting mix. For a more aesthetic appeal, use pine needles or finish off the top with Spanish moss. During the winter months, all of the filler items should be kept as dry as possible. During the summer months, a little moisture would help keep it cooler.
Do not pack any of the materials tightly - roots need air year-round. Both pots should have a drain hole. If your larger pot does not have a drain hole, place some rocks, plastic bottles or Styrofoam in the bottom, so the internal pot is not sitting in water. Always be careful not to over-water. Standing water freezes quickly and most roots do not like prolonged soggy soil.
If you are using a cement or terra cotta pot, it would be a good idea to paint the inside with shellac or water proof paint. This will help keep the pot(s) from sucking out water during the summer and retaining water during the winter.
Cement, brick and flagstone conduct cold and heat that radiates into the pots. Make sure there is air space between these items and the pots. If nothing else, turn a plant pot liner or saucer upside-down and sit the pots on it, keeping them off a solid, nonporous surface.
Did you see a nice plant you would like to give to someone, but the pot or container (grow-pot in nursery terms) is not very attractive? It's not always necessary to immediately re-pot a newly purchased plant, especially if it blooming. Double pot it with a decorative, more attractive container. In nursery lingo, this is called a cachepot (pronounced cash-pot). Use some Spanish moss to fill in the gap. Professional florists do this all the time.
The University of Arizona Mohave County Cooperative Extension is offering the Urban Home Horticulture Class starting Jan. 11 or 12, depending on where you attend the class. Registration is $175 for the 16-week series. For more information, call (928) 753-3788 or visit http://extension.arizona.edu/mohave under Upcoming Events.