There are many forms of topiary. A shaped hedge can be considered to be a topiary, as can a parterre or a standard shrub. However you are probably thinking of a plant shaped into an interesting form, e.g a sphere or series of spheres or an animal shape. Some topiaries are easy to make; others are more difficult. Most of them take time and patience. Another factor is whether you are starting from scratch or pruning an existing shrub or tree. Also, are you growing the plant in a container or in the ground?

The easiest topiary to make is probably to train a vine over a frame. Martha Stewart's website has simple, illustrated instructions on how to make an ivy topiary using a frame. More complicated frames can be constructed to make geometric or animal forms.

These books illustrate some good examples - 

• B. Gallup and D. Reich. The Complete Book of Topiary, pp. 115-156. (Workman Publishing, New York 1987).  
• J Hendy. Quick and Easy Topiary and Green Sculptures (Storey Communications. Inc., 1996).

To make a shrub topiary you can start from a fully grown shrub or from a cutting or a small plant. The Gallup and Reich book (pp. 70-78) has some good hints on starting from a small plant. 

A quicker result can be obtained by starting from a mature shrub. Box (Buxus spp.) is a popular shrub for this approach but many other species. e. g. yew (Taxus spp.) can also be used. 

Another good source on all aspects of topiary making is:

• David Carr. Topiary & Plant Sculpture The Crowood Press, 1989.

Courtesy of the NYBG Plant Information Service