There are lots of ways to do it. By definition, topiary is simply a process used to train plants into unnatural shapes. Topiary plants can be created by training plants to either a stuffed or open wire frame or, since they are living plants, by shaping a plant. Topiaries are always a work in progress, changing from week to week, giving you lots of opportunities to show your creativity. Simple Standard Topiaries First, choose the right plant, one that naturally grows rather upright or forms a central leader that will thicken like a trunk.
Examples are rosemary, geraniums, lantana and myrtle.
Select the strongest, most upright stem and trim off any other stems. Insert a stake as close to the base of the stem as possible and attach the stem to it for support using floral tape. Prune off all the leaves and side shoots from the lower sections of the stem, only leaving leaves on the top area that will form the head. Keep sucker growth from developing along the stem or from the base and allow the central leader to grow until it reaches the desired height. When the topiary reaches the desired height, begin pruning the central leader whenever you prune the side branching.