division 79
Division
A
perennial garden whose owner’s primary objective for the garden
is low maintenance simply should not contain plants that require
division annually or even every couple of years. No worries
though, as there are plenty of perennials that don’t require
division for 3 to 5 years. And many can go 6 to 10 years or even
longer without division. In fact, several perennials would rather
not be bothered at all. However, you should not let division
requirements limit you too much in plant selection. It isn’t as
dramatic a procedure as it might first appear. In fact, it can be very
satisfying, having a rejuvenating effect on perennial and gardener alike.
There is plenty to do in the perennial garden without going around needlessly
dividing perennials. The growing conditions often will affect whether a plant is
going to need division sooner or later. Some invasive plants can be more or less
aggressive depending on the soil, amount of moisture available, and so forth.
The plants will send signs when division is in order: the flowers may get smaller;
the clump may take on the appearance of a traffic jam, with the stems and
branches getting all tangled up; the plant may develop a hole in its center, taking
on the form of a donut; the plant in general may have less vigor; it may flop more,
requiring staking that it never needed in its prime; or it may need division to
keep its spread in bounds. A perennial may also need division simply if the
gardener decides he or she wants more plants, or if generous friends force that
decision.
The perennial division gods once proclaimed that spring-flowering plants
should be divided in the autumn, and autumn-flowering plants divided in the
spring. This gospel stuck, and you see it stated in most of the literature. I’m not
about to overturn tradition! But you gain an entire season of growth if early
spring–flowering plants are divided right after flowering in April or May. If you
don’t mind sacrificing flowers for that year, the plants can even be divided in very
early spring before flowering. Spring division also gives more time for establish-
ment before winter. The tale holds true that autumn-flowering plants should be
divided in spring, and this includes most ornamental grasses. For these reasons I
tend toward spring division for almost everything, whenever possible.
Plants not suitable for spring division include fleshy rooted perennials such
as peony (Paeonia), oriental poppy (Papaver orientale), and Siberian iris (Iris
sibirica), which are best divided in autumn. Siberian iris will tolerate springWhen selecting perennials,
consider how frequently they
will need to be divided. Russian
sage (Perovskia atriplicifolia) in
the foreground and ‘Milkshake’
coneflower (Echinacea purpurea
‘Milkshake’), midground, require
infrequent division—sometimes
not for 10 years. ‘Lucifer’
crocosmia (Crocosmia ‘Lucifer’),
in the background, may need
more frequent division for best
flowering; possibly every 3
years.