Although some newer cultivars don't require pinching, most mums will become tall and leggy if not pinched back. Here's how: Beginning in May, whenever a new shoot reaches seven to 10 centimetres tall, pinch it off using your thumb and index finger, leaving two or three leaves on the shoot. Fertilize plant and pinch back any tall shoots about once a month until mid-July.
上面是从这里抄下来的。