Stumps that are intended as permanent features in the garden need to be preserved to delay the process of decomposition that will occur more rapidly in untreated wood. The New Mexico State University Extension site recommends the use of wood-penetrating preservative on the stump. Another preservation method is the use of weather-resistant polyurethane, as suggested by Kristen Hampshire in "John Deere 52 Backyard Landscaping Projects."
The recommended method for preserving the tree stump is to treat all the above-ground portions of the tree with the selected preservative or polyurethane. Use a brush to coat the cut top surface of the stump evenly. Also coat the bark all the way down to the soil line, making sure the material gets into the crevices. Though the roots will eventually rot since they are in the ground, the entire process will take up to a few years.
The tree stump may be used in its natural state as a raised planter for potted plants. Simply cut the stump to the desired height and coat with the preservation solution. The raised area can also be used as a focal point in the garden by arranging potted plants around the stump. This is an easier alternative to removing the entire stump and replanting the site with new plants.
Hollowed-out tree trunks are ideal sites for planting new plants. As the stump decomposes gradually, it radiates heat that creates a naturally fertile and moist growing environment for plants. The task of hollowing out the stump is laborious, and it is best to request the tree removal service to do this for you when it is cutting down the tree. Coat the outer surface with the preserving material, and fill in the center with good potting soil. Place desired plants in the soil.