To bring it down from overgrown, then
keep it smaller than small.
Several different lilac species are dubbed "dwarf," including
widely-used Syringa meyeri and S. chinensis
hybrids. At 8-15' they are small compared to the common lilacs
(15-20'; perfect to sniff from a second floor window), but not tiny
enough to be cast alongside Snow White. S. meyeri grows to
about 8', S. chinensis to nearly 15'.
So if you want a dwarf lilac to remain less than 8' or a common
lilac to be less than 20', plan to prune it regularly.
This article is for you if you have an overgrown lilac of
any kind:
• First, to bring it down to manageable size,
• Then to keep it smaller than it would if left alone.
Take a look at how-to
A dwarf lilac (Syringa meyeri) is at the right side of
this foundation bed (below). It's been pruned regularly so
it's not as tall as it could be. However, it has bulked up and also
increased its height beyond what's good for this bed. In addition,
a survey of the branch tips shows it has not produced many
flowering stems. That's probably because the former gardeners kept
up with the shrub by shearing it repeatedly through the summer. By
late summer, those shearing cuts were removing flower
buds.
We'll show you how to prune it just once a
year to keep it small and blooming well.
Here's how to reduce it:
What you do in year one, in late spring:
Cut out all the oldest stems after the shrub blooms. That
reduces the height and the bulk.
What the bush does in year one, summer:
New, shorter canes (suckers) grow from the cut-back stubs.
Meanwhile, the remaining original canes produce flower buds for
the next year.
Below, it's a bit of a wild sight after our first cut. The
owners were willing to put up with this gawkiness for one year so
that they would have flowers the next spring. If one spring without
flowers is acceptable, simply cut down all the canes.
Year two, spring: Enjoy the bloom
At the beginning of year two, we had everything we'd aimed
for:
The remaining, too-tall canes were set to bloom, plus
the rest formed a neat mound of new growth (below, orange
dashed line) which will be old enough to bloom next
year.
Year two, late spring: Cut again
The shrub's owners cut plenty of lilac flowers. After the bloom
was done, they cut out all of the too-tall stems that remained.
Below, left: All those tall canes are now on the lawn.
Below, right: What is left consists of branches that grew from the
base soon after last year's cut, plus a thicket of lower shoots
that are new this year.
Then they thinned the thicket of short new stuff coming up from
the base (below).
Below: When we say "remove" and "cut out," we mean to cut
unwanted canes down to ground level.
To thin the thicket of new wood, remove all spindly canes such
as "a" and "b" and even some of the stronger wood, "c". Every weak
and excess cane should be clipped off at ground level.
(More detail on these a-b-c steps in A Lilac's Annual
Cut.)
Year two, summer:
Every existing cane now adds about 6 inches in height. At the
tips will be flower buds for Year Three.
Meanwhile, more brand new suckers develop. In this, their first
summer, they grow to about 30" tall.
This dwarf lilac shows us its growth rate. The new wood has
a paler stem than the old. (Note new wood above the right-hand
arrow.) That's about 6" of new wood we must plan for. We do it by
leaving the shrub 6" shorter after the spring pruning than we want
it to be at bloom time the following spring.
Year three and beyond:
To keep a dwarf lilac small, start out by accepting that it has
the potential to be as big as those at the very top of this page
and that you must prune it regularly. Then, make these cuts once a
year -- it takes about 15 minutes:
Spring: Each spring the shrub will begin growth
with two-year-old canes ready to bloom, plus one-year-old canes
ready to grow a bit taller and set the next year's flower buds.
Enjoy the flowers.
Late spring: Cut the tallest canes to the
ground. Thin out excess suckers. Shorten any remaining cane to
allow it room to grow un-cut the rest of the summer.
Below, left: In year three the dwarf lilac blooms
well and is the right size for this bed. Below, right: A few weeks
after it blooms, we cut out the tallest canes and thin the rest.
One cut per year leaves it ready to grow back to the same
acceptable size and bloom well.
(See more photos of this routine applied to this shrub and also
to common lilac in A Lilac's Annual
Cut.)
Below: What you see here may be the perfect size for a
dwarf lilac. We can open the window and have the flowers' scent
fill that room. Yet the shrub wants to be taller, so learn
to prune it!
No absolute "right" or "wrong" in pruning.
The choice is always yours. Shear a shrub, do more selective
pruning or simply let it grow -- all of these are "right" if the
effort is tolerable and the result is pleasing to you.
Below, left: The dwarf lilac, overgrown. Center: That lilac
in the first stage of being cut back and kept small.
Right: The size it will remain now that it will be cut just once
annually per these directions.
