Getting it to bloom

Why won't my Common Lilac bloom? (and how to make it flower)

Also called common lilac, French lilac (Syringa vulgaris).

More about common lilac

About Common Lilac

Syringa vulgaris · also called common lilac, French lilac · flowering

Common lilac is a large deciduous shrub prized for dense, intensely fragrant panicles of lilac, purple, or white flowers in mid-to-late spring. It needs a cold winter to flower well and performs best in full sun on neutral-to-alkaline, well-drained soil. Long-lived and hardy, it can become tree-like with age and benefits from deadheading and occasional renewal pruning.

Plant type: flowering

Watch for — Poor flowering: Caused by too much shade, over-feeding with nitrogen, pruning at the wrong time, or insufficient winter chill. Lilacs bloom on old wood — prune right after flowering, not later.

The reasons common lilac isn't blooming

Almost every non-blooming common lilac traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding common lilac a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get common lilac to flower

Maximise sun. Give common lilac the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for common lilac and get the feeding right with the common lilac fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Common Lilac flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full common lilac care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Common Lilac blooming — frequently asked questions

Why won't my common lilac flower?

Common Lilac blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make common lilac bloom?

Give common lilac the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does common lilac normally bloom?