Photo credits and licenses
Real photographs from naturalists and photographers worldwide, each used under its own license. Credit: Photo by Tatyana Petrenko / iNaturalist (CC BY). How photos are sourced →
Rhododendron
Rhododendron
Rhododendron blooms from May through June.
Mature size, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not.
Growing Rhododendron
Plant it in part shade. It prefers moderate water. It is hardy in USDA zones 4–8. Expect it to reach about 5.9 ft tall and 5.9 ft wide at maturity, in roughly 5 years.
When to plant Rhododendron
Plant Rhododendron in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. For the middle of its hardy zones 4 to 8 range, spring means March to May and fall means August or September. Once settled, it blooms from May to June.
Month-by-month timing for your zone is on the planting calendar: for the middle of its range, start with zone 6 in March.
Comes in 12 varieties across 6 colors
Same plant, same care - pick the color you are growing.
Good to know about Rhododendron
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats, and horses: all parts and the nectar hold grayanotoxins. Even a few leaves can cause vomiting, weakness, and dangerous heart effects. per ASPCA
Worth knowing
Drainage decides everything. The same soggy, poorly drained soil the shallow roots cannot handle is what lets root rot, the top killer, take hold. Plant high, never wet. per Clemson and University of Maryland
Diagnose dieback before treating
Branch dieback has more than one cause: a wet-weather Phytophthora blight (UConn) or a canker fungus on stressed plants (Clemson). Diagnose which before you spray. per UConn and Clemson
Prune right after flowering
It blooms on old wood and sets next year's buds in summer, so prune and deadhead right after the flowers fade. A later cut costs next spring's show. per Clemson and UGA
Lace bug worse in sun
The main pest, lace bug, stipples the leaves pale gray and is far worse on hot, sunny, dry sites. Dappled shade with afternoon relief keeps it in check. per Clemson and UC IPM
Needs acid soil
Grows only in strongly acid soil, roughly pH 4.5 to 5.5. Too high and iron locks up, so new leaves yellow between green veins. Test before amending. per University of Maryland and Clemson
Nectar makes 'mad honey'
Bees that work rhododendron flowers can make grayanotoxin-laced 'mad honey', which has sickened people. The nectar carries the same toxin as the leaves. per PubMed Central and NC State
What pairs well with Rhododendron
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
Windflower
Takes part sun to part shade and moderate water; blooms in early spring, before this one opens; low at 6 in, to carpet the ground beneath.
Cyclamen
Shares part shade and moderate water; blooms in early fall, extending the bed's season; low at 8 in, to carpet the ground beneath; pink sits close to purple on the wheel.
Primrose
Shares part shade and moderate water; opens in early spring and overlaps into this one's season; low at 8 in, to carpet the ground beneath; yellow against purple, for contrast.
Wishbone Flower
Shares part shade and moderate water; overlaps, then carries the display into early fall; low at 10 in, to carpet the ground beneath.
Bacopa
Takes part sun to part shade and moderate water; overlaps, then carries the display into mid fall; low at 6 in, to carpet the ground beneath; its white flowers settle the purple.
Lily of the Valley
Takes part shade to full shade and moderate water; opens in mid spring and overlaps into this one's season; low at 8 in, to carpet the ground beneath; its white flowers settle the purple.
Snowflake
Takes part sun to part shade and moderate water; blooms in early spring, before this one opens; lower at 12 in, for the front of the border; its white flowers settle the purple.
Lobelia
Takes part sun to part shade and moderate water; low at 8 in, to carpet the ground beneath; overlaps, then carries the display into early fall.
Explore similar plants
You might also like
Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.