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Sale Hydrangea Diadem

Hydrangea serrata 'Diadem' (mountain hydrangea)

Next available Monday or Tuesday

Unavailable Available Only few left Out of Stock Pre-order

Diadem mountain hydrangea is the daintiest lacecap I've ever seen.

I find Diadem displaying light to medium pink flowers typically, but I once spied it offering light blue lacecaps. I've taken some pics to show you the pastel color range - it seems to hold pink colors very well, but, as on all mountain and bigleaf hydrangeas, color is dependent on pH and aluminum availability.

One thing I love about it is the free flowering nature - meaning Diadem is still throwing out flowers randomly here and there. As I write on August 11th, four more flowers are about to open - this jewel of a hydrangea has been tossing up a small group of flowers like this ever since May!

Diadam is a serrata type and therefore more reliably cold hardy than its macrophylla sisters.

With purple-plum autumn foliage, Diadem is also one of the few mountain hydrangeas with good fall color. Purple autumn raiments for Diadem, how royally fitting.

  • petite light pink (or light blue) lacecap
  • single specimen and accent use
  • large container use
  • grouping and massing - large swaths
  • flower and shrub borders
  • tolerant of salt spray so great for maritime climates
  • heat tolerant
cut flowers, long flowering period
Common Name
mountain hydrangea
Other Names
'Hashikuzu', 'Hoshkuzu'
USDA Hardiness Zones
flowering shrub, deciduous
Growth Rate
Flower Color
pink, blue
Showy Flower?
Flower Season
Leaf Colors
  • Spring: green
  • Summer: green
  • Fall: purple
Fall Leaf Color Quality
Native to USA?
Native To
Soil Moisture Requirements
moist-but-draining, no standing water
Soil pH Requirements
acid, neutral, alkaline
Light Requirements
sun, part shade, shade
To Make It Thrive
Give Diadem hydrangea rich soil plus consistent moisture in a soil that drains. It may require extra watering, but avoid standing water. Grow it in full shade or afternoon shade in the deep south (zones 8 and 9), not only for the foliage, but so the flowers don't get sun scald. Full sun is okay farther north. For flowering in cold climates, situate it in a warm, sheltered location. During the ups and downs of spring temps here in Zone 8a - we cover to protect flower buds.
Plant Patent
The flower color is not as you described, it's paler.

Yes, I've come to the conclusion that Hydrangeas don't like to have their flower color profiled and clinically categorized like we humans try to do to everyone and everything. Please keep in mind that flower color varies widely and wildly depending on soil pH and the amount of aluminum actually in your soil, the amount of time aluminum has been available to the plant (did you add Al only last month?), the unique propensity of how each cultivar reacts to Al, and if the flower heads get a touch of sunshine as they age.

The flower color is not as you described, it seems darker to me.

Same issues as when it's paler; say after me, "a-lum-i-num-a-vail-a-bil-i-ty plus time plus cultivar plus a touch of sunshine."

This is science for sure, but also a whole lot of art. Enjoy the outcome Mother Nature deals!

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