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Lilac Renovation

Thanks for this service you have. I can't seem to find any information on lilacs. We live just north of Hamilton ON  . We have lilacs on our lot that have been there for 22 plus years . They are large yet have lots of new growth at the base . We thinned them out but now they are spindly at the top. Is it possible to cut them down to 5-6 feet tall without harming them?
 
Looking forward to your reply,
 
Peggy


Doug says


Lilac renovation is like pruning any large and old tree.

Understand that new growth comes from what are called "juvenile buds" - these buds lay dormant under the bark of the plant until they are called on to grow because of hormone stimulation. We create that stimulation when we top prune a plant - when we cut off the growing tip of a plant.  The hormones in the plant say "Oh -  we just lost our top - better produce another top" So they start several buds just behind the cut section.  This is how we thicken up annual plants - cut off the leader and new growth appears.

As a tree ages however, those juvenile buds age as well - and they lose the ability to respond.

My guess is that your lilac - at 20 years of age - has lost most of those juvenile buds in the bottom sections.

So when you cut off the tops, you're going to see no new growth from the resulting woody stems. They will not likely resprout.

What will happen (likely) is increased shoot development from the bottom of the plant so you'll find yourself the proud owner of a lilac thicket of shoots.

You can prune out these shoots and train them into the shapes and forms you want - it's drastic renovation but you can simply cut the older stems right to the ground and allow the new plants to take over in the shape you wish.




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