Forms, or shapes on which to train plants into topiaries, are available in globes, spirals, and even teddy bears and rabbits. Using such rapidly-growing plants as ivies will assure that your form will fill out in a matter of months.
1. Fill the pot. Place a layer of broken terra-cotta pieces or loose gravel in the bottom of a decorative pot to provide good drainage for the ivy. Fill the container with good-quality potting soil; tamp down soil.
2. Add form. Place the topiary form into the soil, carefully centering the form within the container. The topiary base should be level with the soil and sit firmly in place.
3. Insert sticks. For a form with a central spine, such as this spiral, use hyacinth sticks to anchor it in soil. Insert four sticks closely around central spine; work into soil. Holding the sticks against the spine, wire to the form with florist's wire.
4. Train plants. If using a hanging basket of ivy, carefully separate the plants into several sections, with each having at least one long trailer. Or, use several small pots of ivy, each with a long trailer. Working with one section at a time, remove enough soil to make room for the root ball; plant the ivy. Pack down the plants, adding more soil as necessary. Continue planting ivy until the pot is filled out. The ivy will quickly spread, so leave space for the plants to grow.
5. Maintain. Using the long trailers, carefully wind the ivy around the topiary form. If needed, secure ivy to the form with cloth-covered wire. To maintain the topiary as the ivy grows, continue winding the trailers around the form. You may need to clip bushy growth to maintain the shape; however, the trimmed ivy will quickly root if you place it in water. (Use these starts to begin another topiary.)
6. To finish, lay live moss around the topiary base, concealing the soil, as well as the form's base. The moss provides a natural protective barrier for the plants, helping them retain moisture. Stick greening pins through the moss to help secure it; water. Continue to water the topiary frequently, and periodically feed the ivy with houseplant fertilizer to encourage growth. The ivy will fill the form within a month or two.