Can tall asters be sheared or lopped off early in the growing season to control height and make them bushier? I have Aster novae-angliae ‘Wild Romance’. I love the color and bloom-time, but would like them shorter.
Yes, asters (now renamed Symphyotrichum) can be pruned. This is sometimes referred to in England as “the Chelsea chop,” and it is a technique that may be used for a number of different perennials, as this article by Bunny Guinness in the Telegraph describes. An excerpt appears here:
“Plants now commonly manicured by their snip happy owners are Campanula lactiflora, sedums, rudbeckias, echinaceas, asters and heleniums. These have their shoots chopped back by around a third in late May/June. The basic rule is that perennials which only flower once should not be chopped or you will lose the flowers; varieties such as peonies, irises and aquilegias.”
Here is similar information previously available from the Colorado State University Cooperative Extension website:
“…control the height and shape of an aster by pruning. Gardeners can pinch asters like mums, regularly removing little bits of new growth until the first of July. However, an easier approach is to cut the aster back by one half in mid-June. At this time, the aster can be shaped. Outer stems can be cut lower than inner ones to produce a nice mounded plant. This shaping tends to encourage bloom near the base of the aster and discourage ugly brown stems. Although this pruning may sound extreme, it tends to delay flowering by only a few days and produces a much prettier plant.”