pinching or cutting back can be used to achieve similar effects, I generally opt for
cutting back rather than pinching. From a time standpoint, I prefer to cut
something back once, rather than pinching and then having to come back and
pinch again, and perhaps again, to create the desired effect. Certain perennials
do seem to respond better to pinching than to cutting back, although from a
physiological point they should be the same.
Most of my work concentrates on the effects of cutting plants back once
before flowering. Perennials can be cut back at different times, or several times,
for different effects, but in most cases pruning only once makes sense from a
maintenance standpoint. Pruning of plants before flowering (by half or
two-thirds) is generally done in early to mid-June, because this is also the time
when many spring-flowering species can be pruned after flowering. It gives the
landscape contractor, for example, a time frame in which a large number of
perennials can be pruned during one maintenance visit to a garden. Keep in
mind that, again, this is an attempt to simplify a rather complex area of pruning.
Pruning in early June will delay the flowering of many summer bloomers, but
pruning earlier in the season may be preferable if no delay is desired. In warmer
climates you may need to prune earlier because of faster growth earlier in the
season, and you also may need to prune plants more heavily in such climates to
effectively reduce their height. The longer growing season in the South means
late-flowering plants can be pruned later into the season to further delay
flowering, while such pruning in cooler climates may result in plants that don’t
have a chance to flower before snowfall.
Timing of cutting back is an interesting issue and one that is open to lots of
fun and experimentation. The cutoff date to stop pruning perennials so that they
will flower before cold weather, or so they will or won’t be delayed or by how
much, is not known in most cases. General pruning dates are often given without
sound experience, such as “don’t prune after the 4th of July if you want flowers
before frost.” I have experimented with a variety of different pruning dates for
different species, and the results are provided in the Encyclopedia of Perennials.
With some plants, cutting back before flowering will decrease the floral display
or the vigor of the plant or both. Some perennials, if cut back too often, or by too
much, or too late in the season, may not flower nicely, or at all, or they may be
stunted. Others may start flowering as soon as pruning stops no matter how lateBoltonia asteroides ‘Snowbank’
pruned to create a layered
effect, stepping up nicely to
Eutrochium maculatum
‘Gateway’ behind it.(opposite) ‘Alpha’ phlox
responds well to pruning for
height control and to delay
flowering. Shown here is a
pruned plant in the foreground
with an unpruned plant in the
background.
114 PruninG Perennials