compact habit, less need for staking (if any is required), and staggered bloom
time if desired.
Cutting back autumn-flowering plants for height control is normally done in
mid- to late June in the Midwest, generally when the plants are 12–16 in. tall.
Cutting back can be done later, depending on the usual variety of factors. Most of
the time the plants should be cut back by half, but you can prune back two-thirds
or more depending on the plant and your objective. Pruning later may involve
simply removing 4–6 in. from the tips of the plants.
Asters are among the first autumn-flowering plants that come to mind for
cutting back. They are one of several perennials for which pinching is often
recommended, but that respond just as well or better to cutting back. I find that
cutting back these late-season beauties by half or two-thirds when the plants are
12–16 in. tall is more effective than pinching. The outer stems can be cut lower
than the inner ones to create a more rounded habit and reduce the ugly legs
usually associated with asters. Cutting back can eliminate the need for staking
on most Symphyotrichum cultivars, but some of the extremely tall ones may
require it even with pruning, depending on the soil and weather conditions.
Once cut back, they usually flower at a sturdy 3 ft. or so. You can also select asters
that won’t require cutting back. One I prefer is the late-season (mid-October for
us) Aster tataricus ‘Jindai’. It usually reaches only 4 ft. in height and doesn’t need
cutting back or staking. Lower growing forms can also be used, such as Symphyo-
trichum novae-angliae ‘Purple Dome’, which reaches only 18 to 24 in. in height.
Sedum ‘Autumn Joy’ is often pinched for height control, but it can also be cut
back by half in the spring, when plants are 8 in. tall (in the Midwest this is usually
the first week of June). Plants will have more but smaller flowers. Pruning also
helps prevent flopping on plants growing in part shade or very rich soils.
One usually associates chrysanthemums with pinching, but they can also be
cut back effectively. I don’t use many mums because of their lack of hardiness,
but I have a few that I love that are tough as nails and quite attractive, and some
do fine without any pinching or cutting back. I discuss these forms in more detail
in the next chapter and in the encyclopedia.
When grown in the South, Eutrochium purpureum can be cut back to 12 in. in
early June and will flower at about 3 ft. in early August, compared to its typical 15
ft. or more mature height. In the Midwest, I pinch Eutrochium maculatum
‘Gateway’ for outstanding full plants with smaller flowers. A variety of
Cutting back autumn-flowering
perennials such as symphyo-
trichum: (left) cut back by half
to two-thirds in early summer
for height control; (right) plants
can also be shaped, if desired.cuttinG BacK 117