How to Prune Lilacs correctly addresses the different reasons to prune. Each may have it’s own method.
Many complain that their large lilac is not blooming and there can be many reasons why, which I talk about in this post Lilac Not Blooming?
One reason can be that your lilac has not been pruned well or correctly.
Let’s start with the reasons to prune.
the Lilac has been neglected for years
Common Lilacs can last for decades but they bloom best on wood that is under 5 to 6 years old. They will bloom less and less on wood that is older. Plus the blooms are usually too high to enjoy once that old.
For older lilacs that have not enjoyed good annual maintenance a more severe renovation prune is in order.
A good time to do this is in early Spring before new growth begins. Check to see if your lilac has been grafted. Check the main trunk of the Lilac and see if there is a bump and difference in bark. That would be the graft union.
Grafting is where you join a scion of one cultivar to the root stock of another. If you discover it is a grafted Lilac be sure to remove all suckers from around the base.
The shoots or suckers coming up around the base will not be the same bloom type as your main Lilac.
Never cut below the graft joint. If the lilac is not grafted you can cut the entire plant off at the ground but don’t expect any blooms for a couple years.
That is the most drastic method but it does work.
Less intense renovation prune
You can also do a renovation prune over a 3 year period. When pruning this way cut out any dead or weak canes, cut out 2/3rds of the suckers or shoots coming up at the base, leave 1/3 for future blooming stems.
You can actually dig the suckers up and pot them to make more lilacs if you wish, they actually mature faster than taking cuttings and rooting them.
Cut back 1/3 of the older lilac canes or branches. The following year cut out the next 1/3 of the oldest branches then the final year cut back the last of the oldest branches.
Doing this in 1/3’s will let you have blooms and still cut back the old worn out branches fully renovating the lilac.
Some say to have only about 10 canes per bush for best health and others say 2 or 3. The lilacs I have cared for have between 5 and 10 canes and bloom beautifully.
Cutting Lilac blooms to bring into the house is a great way to keep your plant healthy. Make the cut at the base of the flowers. This is similar to deadheading but you are cutting off the flowers before they are dead.
The beauty of cutting the flowers is you keep spent blooms from sucking energy from the rest of the lilac. And you get to enjoy their sweet perfume in your home.
Deadheading should be done as soon as possible after the flowers fade if you haven’t already cut them to bring into the house. The old flower cluster should be cut off at its base, just above the two new shoots that angle out from the stem that ended with the old flower.
New shoots will grow over the summer, set flower buds, and bloom the following spring.
Just after they bloom is also when you cut out unproductive, misshapen and obviously diseased stems to the ground. Twiggy growth should also be removed.
Thin and remove some canes to give proper spacing for healthy air flow, stimulating robust growth.
Cut out suckers straying to far from the plant, cut them to ground level. I have read that the suckers or shoots that maintain a pencil thickness all the way to the tip are the most productive but I haven’t tested that myself. Keep a good few inches between suckers or shoots.
Tipping is when you cut back to a pair of side shoots instead of at the base of the spent flowers.
You will need to do this if you get a stem that shoots higher than the rest making for an uneven plant. The benefit of tipping is not only a well shaped lilac but the side shoots will put out new growth and flower buds for the following year.
I don’t give a particular month or date as the bloom time of your Lilac can be quite different than mine. Here we typically don’t see lilacs blooming until well into May while just 10 minutes down the road from me they bloomed in early April.
Thus the annual pruning time frame is different for each location.
The dwarf lilacs don’t need much pruning. Just dead head each year to keep neat and tidy. Miss Kim and Bloomerang Dwarf Lilac (reblooming)
I hope you found this helpful. I will try to get photos of each step in time. Or maybe a graphic.