122 PruninG Perennials
producers who grow their thumbnails longer just for this purpose. Cutting back,
on the other hand, involves removing more than 2 in. of growth, sometimes 4 in.,
6 in., or even 1 ft. or more, and pruners are generally the best tool for this.
Pinching involves less time initially, as it is fast work to go through a plant and
pinch it. A plant may require a second or third pinching as well, so in the long
run more time may be required when pruning a plant by pinching as compared
to simply cutting a plant back by half once. As with other forms of pruning,
pinching is best done by cutting the stem just above a node. Ideally the top bud
should point outward; this prevents new stems from growing inward and
creating an entangled, unproductive mess.
It is diffi cult to generalize as to the best time to do pinching. As with any form
of pruning, when to pinch varies according to several factors, among them
climatic conditions, seasonal weather, soil fertility, plant individuality, and the
gardener’s objectives. Pinching usually is performed in May or early to mid-June
in the Midwest; earlier if you are in a warm climate such as California or the
South. If you wish to retain normal bloom time, pinching must be done early in
the season; early spring pinching will be necessary for plants that bloom in late
spring. Any subsequent pinching should be done after 2 or 3 nodes’ growth. If a
delay in flowering is the objective, pinching close to bloom time will give the
desired results. Pinching can be used to stagger bloom time: for example, pinch a
third of the plants in the bed well before normal blooming time; 1 week later
pinch another third; and pinch the rest a week after that. Even pinching plants a
few days apart will create an extended bloom season, though at the expense of a
single abundant display. Pinching perennials when they are first planted often
produces a more compact habit and better branching on first-year plants. With
some perennials, long internodes are a sign that pinching will help improve
growth habit. Perovskia atriplicifolia, for one, should be pinched when it is 12 in.
tall to help control flopping. Physostegia virginiana should be pinched in early
spring to control lankiness, whereas Helianthus salicifolius can be pinched in
early July to create smaller plants for smaller spaces. More exact guidelines are
given for individual plants in the Encyclopedia of Perennials, including approxi-
mate height, time, and frequency of pinching.
Pinching is most commonly used on branching perennials. If we look closely
at our plants, common sense tells us that it would be of no use to
try to pinch an iris, for example, or a daylily, or crocosmia, or any
other single-stemmed perennial. Pinching is of no benefit to plants
growing from rhizomes, bulbs, or corms or to plants that form
basal rosettes. Heuchera does not need its foliage pinched, and we
all can figure out the consequence of pinching the flower stems.
Pinching is not for the rhizomatous polygonatum, either. Some
gardeners feel that plants with a spike or single large head of
flowers are ruined if they are pinched, because the big show will
have been pinched off. The pinched plants may produce smaller
lateral flower spikes, but not always. Some gardeners might find
the smaller flower spikes to be an advantage. I like to pinch or cut
back certain spiked plants, such as Alcea rosea and Lobelia cardina-
lis. Yes, the flower spikes are smaller, but they are more in scale
with the smaller plant that is produced from pinching. In some
cases, such as with digitalis or verbascum, pinching may simply
result in no bloom.
As has been emphasized throughout this book, often several diff erent
pruning techniques can be used for the same plant. Many perennials can be
either cut back or pinched depending on the desired results, timing, season,
gardener’s mood, and so forth. Sedum ‘Autumn Joy’, for example, can be cut inPinching, here showing
chrysanthemum.