When is the best time to prune an azalea? I don't want to harm my
azalea bush or risk removing the flower blossoms for next year.
Like many spring-blooming shrubs, azaleas “bloom on old wood,” which
means they set next year’s flower buds shortly after they finish
blooming this year. If you wait too long to prune them, you will
remove many of next year’s blooms when you prune, especially if you
shear your azaleas.
Other shrubs that fall into this category
include forsythia (Forsythia spp.), Virginia sweetspire (Itea
virginica), mock orange (Philadelphus spp.) ninebark (Physocarpus
opulifolius), quince (Chaenomeles spp.), rhododendrons,
including azaleas (Rhododendron spp.), spring-flowering roses
(Rosa spp.), spring-blooming spirea (Spiraea prunifolia
and S. x vanhouttei), lilacs (Syringa spp.),
and viburnums (Viburnum spp.).
Rhododendron in full bloom
Conversely, shrubs that bloom later in summer and
fall tend to “bloom on new wood,” which means they set flower
buds on the current season’s growth. These shrubs should be pruned
in late winter or very early spring, before they leaf out. Shrubs
that fall into this category include
butterfly bush (Buddleia
spp.), sweetshrub (Calycanthus floridus), beautyberry (Callicarpa
spp.), trumpet vine (Campsis radicans) summersweet (Clethra
spp.), buttonbush (Cephalanthus occidentalis), bush
honeysuckle (Diervilla spp.), smooth hydrangea (Hydrangea
arborescens), peegee hydrangea (Hydrangea paniculata),
repeat-blooming roses (Rosa spp. and hybrids),
summer-blooming spirea (Spiraea x bumalda and S.
japonica) and chaste-tree (Vitex spp.).
'Potters Purple' Butterfly Bush
A rough rule of thumb is to prune spring-blooming
shrubs soon after they finish flowering because most bloom on
old wood, while those that bloom in summer and fall usually bloom on
new wood and can be pruned in late winter or very early spring.
Pruning is an important cultural practice to maintain
the health and appearance of flowering shrubs. Removal of dead,
damaged or diseased wood reduces insect and disease problems while
allowing the pruner to catch problems before they get out of hand.
Keeping the center of the shrub open to sunlight and air circulation
improves the growth habit of the shrub while allowing interior
leaves to dry quickly after rain or heavy dew – which can reduce the
incidence of disease problems. Removing crossing stems eliminates
potential bark damage, reducing the chance of insect or disease
problems taking advantage of that damage. Pruning also forces new
growth, which in most cases produces the most colorful stems and new
flowering wood for future years.
Controlling plant size is low on the list of
reasons for pruning, because pruning is not a substitute for proper
plant selection. Most plants have perfectly lovely natural shapes
that can be enhanced and somewhat controlled through proper pruning
practices; very few adapt well to shearing. Most plants stay healthy
and attractive longer if allowed to grow naturally, so reserve the
hedge shears for formal hedges.
Pink azalea in spring
The process of removing stems at ground level (their
point of origin) is known as thinning, while shortening a
stem from the top is known as heading. Technically, shearing
is just making a lot of heading cuts. Thinning cuts are preferable
because they open the shrub up to sunlight and air circulation.
Heading cuts result in a profusion of growth below the cut that
creates a wall of growth on the outside of the shrub that blocks sun
from the interior of the shrub and impedes air circulation. Even
formally sheared hedges should be opened periodically to encourage
new growth from inside the plants.
Shrubs with a suckering growth habit such as
forsythia and lilac should have the oldest, biggest stems
removed at ground level periodically. Rejuvenate badly overgrown
specimens removing the biggest oldest stems at ground level. This
can be done all at once if the shrub is healthy and vigorous, or it
can be spread out over a three-year period if it is not by removing
one-third of the overgrown stems each year. Keep the sturdiest,
well-placed younger stems and remove those that are damaged, spindly
or too close to one another. New suckers will sprout from the roots
that will have to be similarly thinned later in summer. Hard pruning
should always be done in early spring, before the shrub leafs out.
It is less stressful for the plant, and you can clearly see the
stems when they are leafless.