GardenWizzPlant Care Card

Gum Rock Rhododendron

Rhododendron calostrotum · Shrub

Hardiness
H6 Hardy — very cold winter (to −20 to −15°C)
Position
Full sun, Partial shade
Height × Spread
10–50 cm × 50–100 cm
Soil
acid soils with a pH of roughly 4.5–5.5; well-drained soils high in organic material
Flowering
April–May
Toxicity
poisonous to grazing animals because of a toxin called grayanotoxin in their pollen and nectar; extremely toxic to horses

The Gardening Year

J
F
M
A
M
J
J
A
S
O
N
D
🪴 Plant out
🌸 In flower

Watch out for

Powdery mildew: Improve air circulation and avoid overhead watering; tolerate mild infections or apply fungicide if severe.

Phytophthora root rot: Ensure well-drained acidic soil and avoid planting in heavy clay or frost pockets.

Vine weevil: Use nematode treatments in autumn or apply systemic insecticides to prevent root damage.

Bud blast: Remove and destroy infected buds promptly; ensure good ventilation and avoid late frosts.

Silver leaf: Prune out affected branches well below the infection site and burn debris to prevent spread.

Full guide: gardenwizz.com/plants/rhododendron-calostrotum © GardenWizz — UK gardening encyclopedia