Wednesday Weed – Hydrangea

Every Wednesday, I hope to find a new ‘weed’ to investigate. My only criterion will be that I will not have deliberately planted the subject of our inquiry. Who knows what we will find…..


Hydrangea (Hydrangea macrophylla) in Costa Rica

Dear Readers, in spite of a plethora of native exotic blooms, the lovely folk in Costa Rica have gone bonkers for hydrangeas. They spill out of the little gardens of San Jose (often peeking through the bars that surround urban houses to keep out thieves), burst forth from the manicured grounds of haciendas, and decorate the paths of hotels (as in the photo above from Monteverde). I find it a little confusing: why would you plant hydrangeas when you have heliconias and passionflowers and hibiscus? But of course, the hydrangeas are no further away from home in Costa Rica than they are in London, because this species (Hydrangea macrophylla, or Florist’s Hydrangea) actually comes from Japan.

The flowers of hydrangeas are actually formed of four decorative ornamental petals surrounding five smaller petals ( a ‘tetramer’ surrounding a ‘pentamer’ for those of you with a lust for new words). The outer petals can be white, pink or blue, and the inner flower contains the fertile part of the plant, with five bluish-green sepals.

Photo One by By Holger Casselmann - Own work, CC BY-SA 3.0,

The ‘two-flowered’ head of a hydrangea (Photo One)

It’s well known that the colour of a hydrangea varies according to the soil pH, but I had it round the wrong way. Counter-intuitively, an acid soil may produce a flower on the blue spectrum, an alkaline soil one that is pinker (though see below). I have been pontificating about exactly the opposite for years. That’ll teach me.

The reason for the colour change is that hydrangeas are ‘hyperaccumulators’ – they can take up particular minerals and elements (in this case aluminium) to a degree that would be toxic to other plants. This gives them a clear advantage in particular soils. In alkaline soils the aluminium ions are ‘tied up’ and are hence not available, but in acid soils they are free to be taken into the tissues of the plant. The ions in the metal affect the pigments in the petals, thus causing the colour change – the more aluminium taken up, the bluer the flower.

Note that you can’t change the colour of a hydrangea just by re-potting it – it’s the aluminium ions that cause the change, not the pH per se. Also, some varieties have been bred to retain their pink or white colour regardless of the metal content of the soil. It’s probably best to buy a blue variety and hope for the best if that’s your preference.

Petals of a hydrangea showing the blueing effect of aluminium sulphate solution (Public Domain)

Incidentally, an alternative name for hydrangeas is ‘change rose’. The name ‘hydrangea’ comes from the Greek and means ‘water vessel’ after the cup-shaped seed capsule.

In Asia, pink hydrangeas are much preferred, with a meaning generally translated as ‘you are the beat of my heart!’.

A pretty pink hydrangea (Photo Two)

Now, I should probably make a confession at this point. I have never been overly fond of this kind of hydrangea – they seem to take up a lot of garden space for a plant that is not very useful for pollinators or other creatures and, although florists seem to love those big blousy overblown flowerheads, even when dead, they always seem, well, just a bit much. I have a climbing hydrangea with a much lacier flowerhead, and a Hydrangea paniculata which the bees love for its abundant pollen, but these chaps just leave me cold.

It seems that I am not the only person who is not overly fond of hydrangeas, either: in the language of flowers a hydrangea can indicate ‘boastfulness, cold beauty, heartlessness, and ‘you are cold’. There was an English tradition that the daughter of a  house with hydrangeas growing in the front garden would never marry, and that the plants are generally unlucky. Try telling that to the good folk of East Finchley, you can barely walk ten yards without falling over a hydrangea.

As with many ornamental plants. Hydrangea has a variety of medicinal uses: the root and rhizome are said to be useful in the treatment of urinary complaints. However, it’s worth noting that the plant is poisonous, especially the leaves and buds.

Photo Three by By Holdmacska (Own work) [CC BY-SA 3.0 ( or GFDL (], via Wikimedia Commons

Photo Three

As I have been preparing this piece I have come across several articles remarking that you can make a tea called Amacha from the leaves of the hydrangea  – you are supposed to rub the leaves until they become sweet. It is very popular for the Buddha’s birthday celebrations. Note, however, that the tea is made from the leaves of a different species of hydrangea, Hydrangea serrata. I would be loathe to risk poisoning everyone from the leaves of our common garden hydrangea.

Photo Four by By Chhe (talk) - Own work (Original text: I (Chhe (talk)) created this work entirely by myself.), Public Domain,

Hydrangea serrata, source of the sweet tea for the Buddha’s birthday (Photo Four)

In my internet travels today I have found several paintings of hydrangeas, but none of them quite sum up my feelings about them as well as this painting by Victoria Dubourg, a French flower painter who died in 1926. The heads of the flowers bow under their own weight, and remind me of nothing so much as the big white broiler chickens that I rescued when I worked on a city farm years ago. Those poor creatures had deformed legs from being bred to put on weight so quickly that their frames couldn’t support them, and for me the very largest of the hydrangea cultivars have the same quality of ‘too-muchness’. But still, they have a kind of languid, tubercular beauty that even I can see.

‘White Hydrangeas’ by Victoria Dubourg (1840 – 1926) (Public Domain)

And, finally, here is a poem by Mark Doty, one of my favourite American poets. I love him for many reasons, one of which is his astonishing book ‘Dog Years‘ which is about his dogs, and about losing the man that he loves to AIDS, and how these things come together. And another reason is that he manages to be both funny and profound simultaneously, a clever trick to pull off. This poem was originally published on the Poem A Day website, which I recommend for a daily poetry ‘fix’.


Mark Doty, 1953

Late August morning I go out to cut
spent and faded hydrangeas—washed
greens, russets, troubled little auras

of sky as if these were the very silks
of Versailles, mottled by rain and ruin
then half-restored, after all this time…

When I come back with my handful
I realize I’ve accidentally locked the door,
and can’t get back into the house.

The dining room window’s easiest;
crawl through beauty bush and spirea,
push aside some errant maples, take down

the wood-framed screen, hoist myself up.
But how, exactly, to clamber across the sill
and the radiator down to the tile?

I try bending one leg in, but I don’t fold
readily; I push myself up so that my waist
rests against the sill, and lean forward,

place my hands on the floor and begin to slide
down into the room, which makes me think
this was what it was like to be born:

awkward, too big for the passageway…
Negotiate, submit?
When I give myself
to gravity there I am, inside, no harm,

the dazzling splotchy flowerheads
scattered around me on the floor.
Will leaving the world be the same

—uncertainty as to how to proceed,
some discomfort, and suddenly you’re
—where? I am so involved with this idea

I forget to unlock the door,
so when I go to fetch the mail, I’m locked out
again. Am I at home in this house,

would I prefer to be out here,
where I could be almost anyone?
This time it’s simpler: the window-frame,

the radiator, my descent. Born twice
in one day!
In their silvered jug,
these bruise-blessed flowers:

how hard I had to work to bring them
into this room. When I say spent,
I don’t mean they have no further coin.

If there are lives to come, I think
they might be a littler easier than this one.

Photo Credits

Photo One by Holger Casselmann – Own work, CC BY-SA 3.0,

Photo Two by By Mani Nair – Own work, GFDL,

Photo Three by By Holdmacska (Own work) [CC BY-SA 3.0 ( or GFDL (], via Wikimedia Commons

Photo Four by By Chhe (talk) – Own work (Original text: I (Chhe (talk)) created this work entirely by myself.), Public Domain,






7 thoughts on “Wednesday Weed – Hydrangea

  1. tonytomeo

    Our hydrangeas are PINK! It is too much work to try to get them to be blue, and even then, they are purplish blue, and then revert right back to pink! White is still my favorite anyway.

      1. tonytomeo

        Goodness! I have seen something like that. I get press releases for these sorts of new ‘products’, as if plants are something to be ‘produced’. I used to ‘grow’ them. Some producers ask if I would like samples. Well, no, I do not. I used to take samples, but without exception, the plants are very weak, and do not survive long, ensuring that the consumer will want to buy new ones. Remember when hydrangeas were pink, blue or white?
        If you happen to know a bit of automotive history, you have likely heard that when Chrysler first introduced the Imperial, it was available in only two colors, either black or white. The car was too elegant to compromise with potentially unfitting colors. A few years later, red was added as a third option. Of course, over the years, several colors became available, but Chrysler maintained impeccable standards.

      2. Bug Woman

        I had a brief spell working for Chrysler as a holiday job when I was a student, and a very classy outfit they were too….

Leave a Reply