Large planters look attractive on your porch, patio or in your landscaping, but they do take up a great deal of space. Often, the homeowner does not have room in his home to take the perennial plant inside to protect it from harsh winter temperatures. Solve this problem by insulating your large planters to protect the root ball from dying or suffering damage during extreme cold weather. If you provide your plant with adequate moisture and insulation, it will last in your lawn area for many years.
Save styrofoam from inside new appliances or other types of boxes to use to insulate your large planters. It needs to be at least 2 inches thick to protect the root ball. Take the plant and root ball out from the large planter. Remove any excess dirt inside the planter, and set it aside. Place the styrofoam along the entire interior of the planter, but do not cover the drainage holes. Replace the plant and root ball, and fill in the planter interior with the excess soil. You can also purchase styrofoam at discount or home supply stores.
Remove the plant with the root ball and any excess dirt from the planter, and set them to the side. Line the interior of the planter with bubble-wrap. If the bubble wrap is a thin sheet, you may need to use two layers to insulate it well. Replace the root ball and the excess dirt until the planter is full.
Place the existing planter inside a larger one to insulate it from harsh temperatures. There will most likely be a space between the original planter and the larger one. Fill this space with additional soil. Pile straw or hay on top of the soil to provide further insulation. Take your large planters down from brick walls or any other type of pedestal. Placing the bottom of the planter flat on the ground will insulate it further.