Hydrangea aspera subsp. aspera ‘Macrophylla’

Douglas Justice took today’s Botany Photo of the Day and wrote the accompanying entry as well.

Hydrangeas are popular garden subjects, and the genus Hydrangea has been written about extensively. At least three popular volumes have appeared in the last few years, and the quality of writing and images in those books is impressive compared with what I had to put up with early in my horticultural career. Thankfully, modern hydrangea books take pains to discuss both the wild species and the cultivars (of which there are hundreds). Our collection of hydrangeas at UBC runs to about 20 wild taxa (species, subspecies, varieties, etc.)—most of them derived from Japan, China, and Taiwan—and includes deciduous small and large shrubs (some nearly tree-like) along with deciduous and evergreen climbers.

Michael Dirr, the respected woody plant expert and author of numerous horticultural books, writes of Hydrangea aspera in his excellent Hydrangeas for American Gardens (Timber Press, 2004): "All taxa umbrellaed by this species have large fuzzy leaves and stems, lacecap inflorescences, typically blue or purple in the central fertile flowers, with an outer ring of white to lilac-pink showy sepals. Large, knobbily rounded bud clusters foreshadow the flowers. Depending on one’s aesthetic bent, the bud clusters are somewhat attractive to rather scary". Indeed.

Hydrangea aspera is native to an enormously wide geographical range, from the western Himalayas through Indo-China to Malesia and east to central and western China and Taiwan. Plants vary considerably both morphologically and with respect to cold-hardiness and heat tolerance, which shouldn’t be surprising given that the species is found in both temperate and tropical habitats. The ability of plants to absorb aluminium—and to thereby colour their flowers blue—is also evidently variable. I’ve read that the flowers of H. aspera are unaffected by soil pH, but my own experience with the species (the cultivar in today’s Photo of the Day, in particular) suggests that regular springtime applications of aluminium sulphate effectively cause the fertile flowers to appear bright blue when fully open. They are normally pink, mauve, or lilac-purple in unamended acid soil.

Hydrangea aspera

11 responses to “Hydrangea aspera subsp. aspera ‘Macrophylla’”

  1. Annie Morgan

    I’ve never seen a hydrangea plant in bud! Interesting how they get those rather virulent blue flowers seen in the florist shops.

  2. mike

    Pretty! But for me, I will stick to the deep cobalt blue mop-head hydrangeas.

  3. Katherine

    How interesting! I was always told that you use aluminum sulfate (American spelling) to acidify the soil, and the extra acid turns the flowers blue (as if the flowers are a little pH strip). I use it for increasing the acidity of the soil for my blueberries, too.
    But it is really the aluminum that is working the magic on the hydrangeas! That is good to know.
    I will note that any aluminum sulfate you scatter around the base of a large hydrangea bush is not necessarily spread evenly throughout the bush.
    I have a large bush and it is difficult to spread the aluminum sulfate really evenly. When the flowers bloom, some are deep blue, some are deep violet, some purple, some pure pink, on different sides of the plant. It is easy to see where I scattered more or less aluminum sulfate and where I might have missed a spot.

  4. JoLee

    I’ve had them here in West Linn for about 10 years. They are very strange and wonderful & kids love the fuzzy leaves. Leaves on mine this year are 14″ long.

  5. Eric in SF

    (JoLee, you posted a link to a password-protected gallery)
    So glad you posted a bud shot! I find this species to be overused to the point of irrelevance but I know my opinion on the plant is in the decided minority.
    This is a popular plant here in San Francisco and every so often some enterprising criminal goes through a neighborhood cutting all the nice hydrangea heads and then selling them to the floral wholesalers at our Flower Market.
    I also learned something RE: Aluminium. I also thought the blue was from the acidifying treatment and never connected the Al to the blue color.

  6. Meg Bernstein

    After looking at the picture, I misread deciduous for delicious.

  7. Old Ari

    Its not the aluminium part it’s the sulphuric acid produced when the aluminium salt hydrolyses

  8. elizabeth a airhart

    i dearly love hydrangeas all sizes
    all colors just a favorite
    daves garden has a nice little film
    on planting hydrangeas in the garden
    the close up is very scary indeed
    thank you

  9. Cody

    I have often wondered about the mechanism behind the varying flower color in Hydrangeas. The blue-pink-red color spectrum in plants is typically (always?) generated by anthocyanin pigments. From my understanding, some of these may absorb light differently at different pH levels. So in Hydrangeas, it may be a *lack* of an ability to regulate internal pH that causes the flowers to change color depending on the soil pH. Still don’t have a clear answer for this after speaking with numerous well-informed botanists. Of course, I haven’t bothered to search the literature either!

  10. Mary Ann, in Toronto

    I’m glad I looked long at this lovely photo, before reading the description and comments. It’s interesting that some people find this “scary” — I find it lovely and luscious! And the most wonderful colours, too.
    Different strokes / à chacun son goût !

  11. Donna

    I have this in my garden and absolutely love it, probably because is not at all like the common blue and white mophead hydrangeas. The flower is lovely and it’s foliage contrasts beautifully with other plants in the garden.

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