Prune a dwarf lilac

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Dwarf lilacs, 8'+. Yes they are dwarf, but if 8' is still not small enough to fit your plan, it's pruning time! 

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.

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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.

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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.

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(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.

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(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.

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