Q: I’ve been a gardener for years, but pinching still confuses me. My chrysanthemums and zinnias are lovely until the first strong rain. then they fall over and look dreadful. I know that I'm supposed to pinch them, but just how much and how frequently? — Linda Miller, Potomac, Md.
A: ''Pinch'' means to nip out the very tips of new shoots. On many kinds of plants the young growth is so tender you really can do the job with your fingernails (I use small pruners). The aim is to make the plant produce as many sideshoots as possible. Chrysanthemums should be pinched several times, at roughly monthly intervals, beginning in the spring after you dig and divide the clump. The last pinching should occur between mid-July and the end of the month. Because flower buds start to emerge soon after that, any further pinching will delay bloom and sacrifice flowers. Annual spring division also prevents mums from getting leggy and congested. The ideal time to divide is when new shoots are about 4 to 5 inches tall. By now, of course, yours are probably about a foot tall, but you can — and should — still divide them. First cut back the shoots by about half, then dig up the plant and slice it into segments with a knife; each segment should comprise just one shoot and a cluster of roots. A well-grown fall mum always starts out as a lone shoot in the spring, not a clump of shoots like most perennials. Plant the divisions 18 to 24 inches apart. They will need pinching in about four weeks. Zinnias are a different story: Do not pinch them. To make sure that taller varieties (over 24 inches) stay compact, clip off 10 to 12 inches of stem whenever you harvest flowers or deadhead. This will force new shoots to sprout low on the plants. Since heavy rainstorms can break full-grown zinnias, it’s wise to tie the main stems in midseason to stout 2-foot stakes.