Getting it to bloom

Why won't my Tree rhododendron bloom? (and how to make it flower)

Also called Tree rhododendron, Burans, Lali gurans (Rhododendron arboreum).

More about tree rhododendron

About Tree rhododendron

Rhododendron arboreum · also called Tree rhododendron, Burans · flowering

Rhododendron arboreum is the tallest species in the genus, forming a small tree with stunning deep-red to pink or white flower trusses from late winter to early spring. Native to Himalayan forests from 1,200–3,600 m, it is the national flower of Nepal and needs cool, moist, acidic conditions to thrive.

Plant type: flowering

Watch for — Frost damage to flower buds: Early flower buds (January–March) are vulnerable to hard frosts. Provide overhead protection with fleece or site against a south- or west-facing wall in colder gardens. Buds turn brown and fail to open after temperatures below -8°C.

The reasons tree rhododendron isn't blooming

Almost every non-blooming tree rhododendron 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 tree rhododendron 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 tree rhododendron to flower

Maximise sun. Give tree rhododendron 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 tree rhododendron and get the feeding right with the tree rhododendron 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

Tree rhododendron 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 tree rhododendron care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Tree rhododendron blooming — frequently asked questions

Why won't my tree rhododendron flower?

Tree rhododendron 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 tree rhododendron bloom?

Give tree rhododendron 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 tree rhododendron normally bloom?