Lilac tree looking thin and blooms are sparse

(Question)

We have a lilac tree that is getting thinner looking each year and has fewer blooms each year. As you can see in thd phito, the blooms are not full and there sre several branches with nothing on them. There is also a number of new shoots at the base that gave been allowed to grow. We’re not sure when it was last pruned if at all. It also has the base in the shade and the top is arching out to where the sun is coming through.

What can we do to get the lilac looking good?

 

(Answer)

I think there are a couple of main reasons why your lilac  is not flowering well.

  1. Lilacs need at least 6 hours of direct sun a day. You may need to thin overshadowing trees or relocate the lilac.
  2. The lilac may need pruning or even renovation if it hasn’t been pruned for years. If it hasn’t been pruned for a long time, there is likely a small forest of suckers. Some suckers are essential, but too many small ones can limit flowering. Ideally, there should be 9-15 shoots of various ages. You should take about 3 yrs to reach this ideal with a third of the pruning done each year. Take out the very thickest and oldest suckers and also the thinnest. Cut the suckers off at ground level. The lilac may look somewhat unbalanced in the years it is undergoing renovation. The best time to prune is in the spring as soon as the blossoms fade. If you wait until summer, next years flower buds will have formed and you risk cutting them off. The following link to our library has more information on pruning lilacs http://www.torontomastergardeners.ca/askagardener/lilac-tree-pruning/
  3. Has nitrogen fertilizer been added to the lilac or to the grass surrounding it? Lilacs can grow and bloom on poor soil and too much fertilizer is more likely to cause harm  than too little.Too much reduces flowering and causes excessive suckering.

Thanks for your question.