Woody-stemmed perennials (or subshrubs) should be cut back
to about 4 to 6 in. in the spring or early summer to midsummer if
they have started to die back or grow leggy. Plants in this category
include sunroses, St. John’s wort (Hypericum calycinum), lavender
cotton (Santolina chamaecyparissus), germander (Teucrium
chamaedrys), and thymes. This also applies to lavender (Lavandula),
which may need a hard cutting back in the spring every 2–3 years
to hold a decent habit if the plant has become open and leggy.
Many of these species tolerate cutting back so well that they can be
used for low hedging.
The life of a whole range of short-lived, otherwise biennial
species can be prolonged by several years if cut down immediately
after flowering, before seeds set; hollyhock (Alcea rosea), foxglove
(Digitalis purpurea), and dame’s rocket (Hesperis matronalis) fit into
this category. As mentioned in the chapter on deadheading, a
plant’s primary biological goal is to produce seed to become the
next generation. If this goal isn’t accomplished, the plants put
their energy into vegetative growth, thus extending the life of the existing plant.
PRUNING TECHNIQUES FOR LONG
PERFORMANCE DURING PEAK SEASON
I like to look at spiderwort (Tradescantia ×andersoniana) as an example of a plant
that benefits from several different pruning techniques to perform its best.
When the plants are 12 in. tall (early May in the Midwest), cut them back by half
to reduce legginess; after the first flowering, deadhead the plants, again cutting
them back by about half. Be certain to prune above new lateral buds, if they are
present. Be patient when deadheading spiderwort; the flowers melt away by
afternoon, but many new buds still remain in the flower cluster, so make sure the
plant is finished flowering. After the second bloom from lateral buds, spiderwort
plants may require cutting back by two-thirds or more for healthy new growth
and possibly for another smaller show of flowers. Plants often need to be cut back
by two-thirds or to the ground after the first flowering, skipping the deadheading
step, depending on the growing conditions and the age of the plant. This is
particularly true of older plants subjected to dry conditions, which look pretty
tacky by midsummer. Tradescantia species produces new growth and often will
rebloom with sufficient moisture.
Pruning techniques for long
peak-season performance,
here showing Tradescantia
×andersoniana: (left) reduce
height by half in early May;
(middle) reduce height by half
after first bloom by deadheading
to lateral buds; (right) reduce
height by two-thirds or more if
necessary after all flowering is
completed.Wait until new growth has
broken from the old stems of
lavender before pruning out
damaged sections.cuttinG BacK 119