Lilacs are one of my favorite late spring flowers.They are one of my favorite flowers to decorate with, and we only get them a few weeks out of the year! I love the color, the sweet smell, and the non-nonchalant way they just hang out in a vase, knowing they are awesome. There is nothing more frustrating though than anxiously waiting, and finally, when everyone else has these bushes loaded with big, lovely,fragrant blossoms, and yours either looks incredible sparse, or there are none at all.I’ve had that happen a few times, and it’s always a bummer. I did some research, and realized it’s not just because my plants hates me, and has a personal vendetta. I found quite a few real reasons for “Why didn’t my lilacs bloom?” and how to troubleshoot them!
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Pruning too late, or too much.
While you can find Lilacs that rebloom,this is actually the most common reason a traditional, once a year, Lilac shrub doesn’t bloom. The best time to prune is immediately after they bloom. And,I mean immediately. Don’t put it off like I do folding laundry. Even pruning a few weeks after the last blooms fade can be too late. Lilacs set buds right after they finish blooming the previous year. I have found the best practice is to do it when clipping flowers to bring inside my home, and pruning as you go,shaping the shrub, seems to work the best. However, if you use them simply as yard color, and aren’t out there clipping all of the time, make sure you make a point to trim them for better blooms next year, keeping the shape of the plant, but removing spent blossoms. Otherwise you’ll eventually end up with 30-foot tall bushes with blooms just at the very top. Also, if someone decides to really go to town , and aggressively cuts the bush back to control height, sometimes it takes few years for the plant to recover.
If the bush is getting ready to bloom, and then you get a surprise deep freeze, this can damage the flowers and buds.If you know it’s coming, you can try covering the bush with a heavy blanket if it’s just a quick freeze, otherwise, hopefully next year, there will be better luck with the weather. For us, this is a common practice in Fall as well. Especially with Rosemary.
Lilacs can live a really long time, but can start decreasing blooms the older it gets. This is where aggressive pruning can help rejuvenate it. Lilacs set blooms on newer wood. If you have thick, round, trunk like stems, they are probably too old to produce well. Cut 1/3 of the old wood out with pruning shears(these are my favorite),and do this every year over a stretch of 3 years, and see if that helps. It should help rejuvenate the plant and be another answer to “Why didn’t my Lilacs bloom?”.
Not enough light.
Lilacs need 6 hours a day minimum. When the shrub was planted 8 years ago, it might have been full sun, but if other trees around it have grown, it might not have enough now. Unless it’s small enough to transplant, and the offending tree can’t be trimmed to let more light in, it might be time to plant another Lilac in a second location. There are some great plants you can plant in the shade, just not Lilacs.
Not old enough.
Depending on the variety, it may tale a few years to set real blooms after they are planted. I had a lilac that took 7 years, true story. Everything else was perfect, it just wasn’t feeling it. Finally 7 years in, it has beautiful flowers. Talk about an exercise in patience. Well, not really. I planted 3 or 4 others in the mean time that gave me flowers before that one ever did. It must have sensed my displeasure, and that was getting ready to rip it out to put something else in, and it finally got to work and produced flowers.
Insects and viruses.
Lilacs can get various insects like scale, or borers. Most of those can be easily treated. However, if your lilac picks up a virus such as a blight, and you have multiple plants, it’s better to remove the shrubs to prevent spread. Don’t plant another lilac in its place either.
Generally, what’s in the dirt is perfect for lilacs and they don’t need extra food. In fact, too much nitrogen can hurt blooming. It will produce leaves, but not flowers. If they aren’t blooming, and you’ve ruled out everything else,you can always do a soil test to see if there is some nutrient they are missing.
I hope this helped answer questions as to “Why didn’t my lilacs bloom?”, and some other troubleshooting tips for big,beautiful blossoms the next year!
from Jennifer Rizzo http://jenniferrizzo.com/2017/04/why-didnt-my-lilacs-bloom.html