Japanese maples are a beautiful tree that are cold hardy down to zone 5b if grown in the ground. However, potted Japanese maples tend to lose heat in the pots and are generally only cold hardy down to zone 6b. By planning to overwinter your potted Japanese maple inside, you can grow potted Japanese maples in much colder areas. By insulating the pot and, in very cold climates, adding a little extra heat, your potted Japanese maple should survive the winter and be ready for placement outside in the spring.
Measure the circumference of your potted Japanese maple. If you don't have a cloth sewing tape measure, wrap a piece of string around the top of the pot and cut the string to the circumference of the pot. Measure the length of the string.
Cut a piece of bubble wrap twice as long as the circumference of the pot. The bubble wrap should be at least as tall as your Japanese maple's pot.
Tape one end of the bubble wrap to the pot using duct or gaffer's tape. Packing tape may work, but the adhesive may come loose in cold temperatures. If you use packing tape, use extra tape to ensure proper adhesion.
Wrap the bubble wrap around the pot twice. Secure the loose end using duct tape, gaffer's tape, or packing tape. If you are using packing tape, use extra tape to secure the bubble wrap to prevent it from unrolling as the temperature drops.
Water your tree thoroughly. Water helps retain heat over the winter.
Place your potted Japanese maple in an unheated garage or shed. Although the upper parts of the tree are quite tolerant of cold, the roots can be damaged if exposed to temperatures lower than 14 degrees Fahrenheit. Placing the tree in a garage or shed will protect the tree from cold winds that can draw excess heat out of the pot. If your garage or shed drops below 14 degrees for days at a time, consider using a heating pad under the pot on low to prevent root temperatures from dropping too low.