Fertilising guide
How to fertilise Tree rhododendron (Rhododendron arboreum)— schedule & NPK
Also called Tree rhododendron, Burans, Lali gurans.
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.
Growth habit: Upright, tree-forming evergreen shrub to small tree
What fertiliser tree rhododendron actually wants — and why
Tree rhododendron is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.
An ericaceous (acidic) fertiliser, formulated to keep the soil pH low and supply iron and trace elements in a form acid-loving roots can absorb. Ordinary feeds and any lime lock out iron and yellow the leaves.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for tree rhododendron: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed tree rhododendron, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For tree rhododendron:
Feed with a slow-release ericaceous fertiliser (e.g., Vitax Rhododendron) in early spring. A second light feed immediately after flowering supports bud set for the following year. Avoid high-nitrogen feeds — they encourage sappy growth vulnerable to frost. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.
The dormant-season rule matters more than the exact interval: skip feeding entirely when tree rhododendron is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for tree rhododendron
Follow the ericaceous product's own rate — these are formulated for the plant, so the dilution on the label is right for tree rhododendron. The variable that actually matters is pH, not concentration.
Feeding always goes onto already-damp soil, never dry roots — water tree rhododendron first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the tree rhododendron watering schedule.
Signs you are over-feeding tree rhododendron
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for tree rhododendron:
- Brown, scorched leaf margins from too strong or too frequent a dose.
- White salt crust on the soil surface.
- Soft, lush growth that fruits or flowers poorly.
Signs you are under-feeding tree rhododendron
- Yellowing leaves with green veins (iron chlorosis from high pH).
- Weak growth, poor cropping and an overall pale, stressed look.
- Stunted new shoots in spring despite adequate water and light.
If the symptoms point at watering, light or roots rather than nutrition, the full tree rhododendron care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush tree rhododendron with rainwater (not hard tap water, which raises pH) if salts build up; better still, mulch with pine needles or composted bark and water with rainwater to hold the acidity.
Organic vs synthetic feeds for tree rhododendron
Organic options
Composted pine bark, pine-needle mulch, used coffee grounds and an organic ericaceous feed gently maintain acidity. UK: Vitax or Westland Ericaceous; US: Espoma Holly-tone or Dr. Earth Acid Lovers. Slow, soil-improving, hard to overdo.
Synthetic / liquid feeds
A liquid or granular ericaceous feed — UK: Miracle-Gro Ericaceous, Vitax or Westland; US: Miracle-Gro Acid-Loving Plant Food or Espoma Holly-tone. Pair with rainwater and an acidic mulch for it to work.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising tree rhododendron — frequently asked questions
What fertiliser does tree rhododendron need?
An ericaceous (acidic) fertiliser, formulated to keep the soil pH low and supply iron and trace elements in a form acid-loving roots can absorb. Ordinary feeds and any lime lock out iron and yellow the leaves. Tree rhododendron is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.
How often should I feed tree rhododendron?
Feed with a slow-release ericaceous fertiliser (e.g., Vitax Rhododendron) in early spring. A second light feed immediately after flowering supports bud set for the following year. Avoid high-nitrogen feeds — they encourage sappy growth vulnerable to frost. Feed with a slow-release ericaceous fertiliser (e.g., Vitax Rhododendron) in early spring. A second light feed immediately after flowering supports bud set for the following year. Avoid high-nitrogen feeds — they encourage sappy growth vulnerable to frost. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.
What strength of feed for tree rhododendron?
Follow the ericaceous product's own rate — these are formulated for the plant, so the dilution on the label is right for tree rhododendron. The variable that actually matters is pH, not concentration.
What does over-feeding tree rhododendron look like?
Brown, scorched leaf margins from too strong or too frequent a dose. White salt crust on the soil surface. Soft, lush growth that fruits or flowers poorly. Feeding tree rhododendron an ordinary fertiliser, or growing it in hard tap water / limey soil, is the defining mistake — it triggers lime-induced chlorosis (yellow leaves, green veins) no amount of feeding fixes until the pH comes down.
Should I flush the soil of tree rhododendron?
Flush tree rhododendron with rainwater (not hard tap water, which raises pH) if salts build up; better still, mulch with pine needles or composted bark and water with rainwater to hold the acidity.
Keep reading
- Tree rhododendron care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water tree rhododendron — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise lobelia erinus 'techno heat blue'
- How to fertilise tagetes patula 'boy orange'
- How to fertilise tagetes patula 'janie bright yellow'
- All 6887 fertilising guides in the Growli library