Purdue University's Department of Horticulture recommends diluted glycerin as the best method for preserving branches with leaves. The limbs drink in the glycerin and distribute it throughout the inner structures of the branches and foliage. The university recommends using one part glycerin to two parts water. Although the glycerin adds a brownish hue that darkens the foliage, it preserves most of the color and helps the limbs and foliage retain their suppleness and pliability. Scrape the bark off the bottom few inches of the branches, then stand them in a container filled with several inches of the glycerin solution. You may need to add more solution as it is drawn into the limbs. Preservation is complete when the limbs stop taking in the solution.