Pinching mums back allows the plant to produce more flowers, and forces the plant to maintain a compact shape. Most of the classic football mums that you can buy at garden centers have been pinched back throughout the spring, so that the plants hold a pretty, domed shape and are packed with blooms. However, many modern types of mums are bred to grow in that classic shape and do not require frequent pinching. If you'd like to pinch back your mums, start in the spring when your plants are a bit less than one foot tall. Use a sharp, clean pair of shears to cut back the entire plant by about half. You can repeat this process every two to three weeks until mid-summer. In the fall, don't pinch back your mums, but do deadhead mums by removing faded flowers. If you want to grow a more natural-looking garden, you don't have to pinch your mums back at all! They'll still thrive without pinching, and will grow in a taller shape and "branchier" look.