Select a rosemary plant that is no taller than 1 foot and plant in a 4-inch diameter pot. Place the plant in a sunny location, such as a south-facing window, and grow for about two months without cutting or until it reaches 2 feet tall. Turn the plant every day so all sides receive the same amount of light, helping it grow evenly.
Place a wooden stake in the pot and tie the plant to the stake using twist ties or pieces of twine. Retie the plant as it grows. Cut off any wild, side shoots, but keep the leaves on the trunk as it is growing.
Water the rosemary plant two to three times weekly to keep the soil moist. Provide humidity by setting the pot on a pebble-lined water tray that is filled halfway with water.
Fertilizer with a water soluble higher phosphorus food, 15-30-15, once a month. Water well after applying.
Pinch off the top 1-inch tip of the trunk once the rosemary plant reaches at least 2 feet tall. This will stop the plant from continuing to grow upwards. Then strip off all the leaves and cut off all of the shoots from the bottom two-thirds of the plant. Leave the top one-third of the plant for shaping.
Shape the top one-third shoots into a rounded form by pinching off no more than 2-inches from the tips. Use your fingers or small clippers to shape the plant. As you work, continually turn the plant to keep the shape even on all sides. Keep your rosemary topiary watered and fertilized and keep in a sunny location. Keep the tips pinched or cut on a regular basis to keep the shape.