Master Gardening – When To Prune Lilacs


With Spring finally peeping her head out I thought it was a good idea to bring back the post on the When To Prune Lilacs.   Click here to see How to Prune Shrubs

Lilacs are soon to be in bloom and their unmistakeable fragrance will fill the air!

Master Gardening – When To Prune Lilacs

Today we will discuss how to prune Lilacs (feeding another post).  Hopefully this information will help you keep your Lilacs looking their best which will provide great blooms every year.

There is only ONE time of the year to prune a Lilac….RIGHT AFTER it blooms!  NOT  a month later, NOT in summer and NOT in Fall.  The only time to to prune Lilac’s isRIGHT AFTER it blooms.  Note: Dwarf Lilacs rarely  need pruning…they do not get out of control.  All you need to do is cut off the dead after blooming.

Why is that?

****Early blooming shrubs develop their flowering buds during the summer and fall of the previous year (a.k.a. “old or last years wood). It’s what is meant by “flowering on old wood”.    Summer and fall flowering shrubs bloom on new wood or stems that grew the same season as flowering.

Lilac’s belong in the shrub group of early bloomers…shrubs are called  “early flowering shrub. These are shrubs that flower before June 15th (includes lilacs, weigela, spirea, forsythia, viburnum, St. johns wort, red twig and yellow twig dogwood, deutzia, kerria, mock orange). Pruning should be done immediately after flowering.  If you prune this shrub group in winter or early spring (before blooms) it will remove the flower buds and the current season’s flowers.

Why aren’t my lilac blooms as large as they use to be? Why doesn’t it bloom anymore?

  Lilacs require at least 6 hours of full sun.  The largest lilac flowers to bloom are on stems that are not more than 5 or 6 years old. As the stems get older, the flowers become fewer and smaller, and more out of reach. But with proper pruning, a lilac can produce flowers reliably for decades. What technique you use depends on the age of your shrub.

What are the Pruning Techniques?

An annual maintenance routine keeps plants vigorous.

Pruning is a good thing….
promotes new plant growth
maintains plant size
encourages flowering
removes diseased or dead limbs
helps control insect and disease problems
and relieves cabin fever.

There are two methods:  1) Rejuvenation; and 2) Renewal


This method is for lilacs, weigela, spirea, forsythia, viburnum, St. johns wort, red twig and yellow twig dogwood, deutzia, kerria and mock orange.

It is good for those lilacs that have seen better days, it is the complete cutting down of all stems to 4 to 6 inch stubs (hard pruning).  It is done when plants like lilacs becometoo large, with too many stems and should be done early in the year. In other words, the shrub is a tangled mess of stems and completely grown out of control and very little flowering.   This method is done once every 4-5 years.

Master Gardening – When To Prune Lilacs 2

You prune back ALL the  stems to about 4-5″, leaving you nubs.

This is often painful on the owner, but it is not painful on the lilac shrub.  Your lilac brush will come back like a new baby!


Renewal pruning is done over the course of three years, it is less severe and will bring your lilac back to a healthy flowering state (and less shock to the owner).

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1st year:  Take 1/3 of your lilacs old wood stalks down to ground, and trim remaining branches back 2-3 feet

2nd year: Take another 1/3 of old wood stalk down to ground and after flowering cut back new growth 1 -2 feet

3rd year:  Do the same thinning process (remove 1/3 of oldest branches) and cut back new growth after blooming.

Each year after: trim back new growth after blooming, don’t take any stalks down to ground just reduce height.

Use the guide below to show the angle your cuts should be when trimming back the remaining branches.

  Master Gardening – When To Prune Lilacs 4

 Remember: If you do this technique much later (like spring and after) you are cutting off all of next spring’s luscious blossoms in the process.

This  may sound funny, but  my plants in my garden are like my children! We need to be their parents and do what is “right” for them, not  for us.  That is a sign of a Master Gardener.

If you have any question fell free to ask and I will be more than happy to answer them.