Japanese Lilac not blooming

(Question)

Dollard des Ormeaux QC ( west end on Island of Montreal)
Planted 5 years ago.
Full sun
At the base of the tree I’m growing Thyme is that counter indicated? Very few blooms this year, not over watered or fertilized ; except I have fertilized the thyme to encourage growth could the latter be the problem?

Thank you,

 

(Answer)

Japanese Lilac, Syringa reticulata, are a beautiful tree in any garden.  They have very few specific requirements in order to thrive.  Full sun (minimum of 6 hours), soil with good drainage, and regular watering should keep them fairly happy.  They are quite tolerant of most soil types, dry spells, pollution, de-icing salt, and are generally disease & pest resistant.

All that being said, there are a few reasons why this tree may not be blooming for you.

  1. The age of the tree – many young trees take 5 or more years to get settled in after transplanting and only when they reach a more mature stage will they flower consistently.
  2. Pruning – this tree flowers on old wood, meaning the flower buds were formed the previous season.  So, if your tree was pruned in the late summer or early fall last year or in early spring this year, the flower buds would have been cut off.
  3. Fertilizing – feeding the thyme beneath the tree could encourage vegetative growth rather than bloom production depending on the type of fertilizer used.  Excess gets washed downward through the soil so would have reached the tree roots once it passed through the fairly shallow thyme root system.
  4. Weather – as the flower buds are produced the year before, any dramatic change in current spring/early summer weather or temperatures can cause the flower buds to abort.

Going forward, I would suggest you continue to water it regularly, not prune at all this year and consider feeding only the tree (not the thyme) to encourage bloom production next year.  You can do this by using a high phosphorus fertilizer, something with a higher middle number (5-30-5 as an example).  The use of fertilizer spikes driven into the ground around the tree will deliver the nutrients directly to tree roots and shouldn’t impact the thyme – these can be easily purchased in most larger nurseries, hardware stores or even online.  Buy the spikes for flowering trees & shrubs and follow the instructions on the package exactly.

Good luck.