techniques can be used on other natives to control their heights, and this is true
of many perennials.
Gardeners sometimes have different techniques for the same plants, depend-
ing on their objectives or their situations. For instance, boneset (Eutrochium
perfoliatum), great blue lobelia (Lobelia siphilitica), and ironweed (Vernonia
altissima) can be cut back by half when 4 in. tall and then by half again when 16
in. tall. Or, great blue lobelia can be pinched around the first of July, and iron-
weed can be cut to the ground when 2 ft. tall or cut back by 1 or 2 ft. when 4 ft. tall
to stagger and delay flowering. A good way of demonstrating that pruning
methods, as with many gardening techniques, are not set in stone.CUTTING BACK TO REGENERATE OR EXTEND THE
LIFE OF PLANTS
A regenerative pruning cut can lead to a more vigorous plant and even a longer
life in certain species. Richard Hansen and Friedrich Stahl, in their book Perenni-
als and Their Garden Habitats, write that certain short-lived perennials—Centran-
thus ruber, Coreopsis grandiflora ‘Badengold’, Coreopsis lanceolata, Gaillardia
×grandiflora, and Leucanthemum maximum among them—flower themselves to
exhaustion and are consequently unable to form buds for the following year’s
shoots. To avoid this situation, Hansen and Stahl recommend that the whole
plant be cut back to stimulate vegetative growth. In the Midwest, cutting back in
late August or early September should allow enough time for growth to emerge
before cold weather. This same principle could apply to a wide range of perenni-
als. New growth produced from cutting a plant back is more vigorous and less
stressed than the old dying foliage, and it is likely to be less prone to disease and
weather damage.This Eutrochium maculatum at
Saul Nursery in Georgia was cut
to 12 in. in early June. It flowered
at about 3 ft., rather than the
typical 15 ft.
118 PruninG Perennials