Answer: When the plants have finished blooming and frost has killed back the tops, simply trim them off "crew cut" style at the base. Next spring when they begin to grow again you will need to pinch or trim them periodically to keep them bushy and to encourage more bloom formation. To do that, nip off the tip (maybe an inch or so) of each branch down to just above a leaf. You can use your fingernails or scissors or hand clippers. Once you have done this a few times you will see the pattern to the new growth. When they become bushy it may be tedious to do each tip individually and this is when they are sometimes sheared. Pinch them back occasionally (maybe every few weeks) until the middle of July and then let them grow.
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