Lottah Nursery Tasmania, Australia
Lilacs perform quite satisfactorily in their natural habitat
without any pruning; species under cultivation do not generally
require much attention.
The hybrids and selections made for larger flower trusses usually
benefit from some pruning to improve flower quality as the plants
mature.
Pruning S. vulgaris and S. x hyacinthiflora
hybrids
Space permitting, these cultivars are best grown with multiple stems
to enable renewal pruning on a regular basis when flowering capacity
is past their prime. Somewhere from 6-12 shoots are optimal.
There is probably no necessity to prune in the early years apart
from removing competing shoots. As the plants mature remove 10-20
percent of the main stems annually so that there will always be no
older than 5-6 year old main stems to produce the best
flowers. Reduce overcrowing in the centre to encourage air
circulation and let in the light.
After flowering the spent heads require removal to prevent seed set
which will divert energy that should go into more vigorous growth
and flower initiation for the following season.
Is there a 'correct' way of pruning these lilacs? Not that we know
of. Many means will achieve the same ends, which is large quantities
of high quality flowers. Plate 43 image of 'Cheyenne' in Fiala's
book is fairly close to our ideal lilac shrub.
Pruning S. x 'Lotta' (and other repeat flowering
cultivars)
Because of the repeat flowering characteristic this hybrid needs to
be treated differently. More experienced growers suggest shearing
the plant lightly after flowering to enable fresh growth for the
secondary flowering; in any case the spent flowers need removal
after they peak.
We feel that removal of some of the mature stems in Winter would
encourage vigorous new growth for the best flowers, even if this
means loss of some flowering capacity the following Spring.
S. x prestoniae
These hybrids do not generally sucker so renewal pruning of main
trunks will not be possible. They are best grown as shrubs or trees
with multiple trunks; only corrective pruning is needed for shaping
and to reduce crowding.
S. reticulata
reticulatas grow as trees in their natural habitat; under
cultivation they may be grown as shrubs or as trees; shaping and
corrective pruning in the formative years is probably all they
require.
Dwarf forms
The smaller lilacs do not generally require pruning although doing
so might encourage better flowering from vigorous new growth.
External Link: More on pruning
22063 (2, 7, 10, 1127)