Pink hydrangeas will turn blue.


The color of your hydrangea flowers is determined by the acidity of the soil they’re planted in.  That is it. That’s the only reason.  So if you wander into Costco looking to buy yourself some pillow case sized bags of potato chips, half a cow, 35 bottles of Windex and a jar of pickles big enough to drive … don’t pass up on the potted pink hydrangeas just because they aren’t blue.  You can change that. You can turn your pink hydrangeas blue.

(Speaking of potato chips did you try a new food? Did you send me a photo of it? A blog post featuring allllll the new foods you tried (the good, the bad, and the ugly, coming up in a week or so!  Don’t forget to include a little description of what you made and why in the email. Send photos to [email protected])




Generally speaking you can turn those pink hydrangeas blue just by changing the acidity o the soil they’re in and if they’re in a container it’s even easier to do.  Problem is, you can’t change the colour that the flowers are once they’ve bloomed.  What you have to do is change the acidity of the soil before the flowers bud and bloom.

It’s not hard but you do have to buy one special ingredient.  Love.  Just kidding.  You can’t buy love unless you’re Rupert Murdoch.

What you do need to buy is Aluminum Sulfate, which sounds like the kind of thing  you could only find in a lab, but you can find it right there in gardening aisle of your local hardware store, or garden centre. It’s perfectly safe (and in fact it’s used for purifying water) and it’s cheap.



If your hydrangea bush still looks like this you still have time to change the colour of your flowers.  If they grow pink even though when you bought your hydrangea it was blue, this is why …

Soil that has a pH above 6.0 will produce pink hydrangeas. Soil that has a pH below 6.0 will produce blue hydrangeas. So if you bought a potted hydrangea that was blue, once you put it in your soil it didn’t have the proper acidity to grow blue anymore.  So how do you know what the pH of your soil is? You can buy a little kit that’s like a pool testing kit to check the pH of your soil. You just put a little soil in the container, add the pH testing powder, some water and give it a shake.


phtest ph-test-results


I tested the soil around my hydrangea plant and it’s pretty off the mark for a blue hydrangea, with a pH of between 7 and 7.5. So that’s going to produce a very pink hydrangea. Which is nice, but it’s also nice to experiment a little. I want to try to get blue hydrangeas this summer which means dropping that pH to below 6.

Aluminum lowers the pH of soil so I need to add aluminum. Since crushing cans and turning them into powdered form seemed like kind of a pain, I just bought a container of Aluminum Sulfate. Adding this to soil is the easiest way to get a blue flower.

But honestly, you don’t need to test your soil for acidity.  If your hydrangea flowers are pink, you know that your soil acidity is wrong for producing blue flowers, so just grab some aluminum sulphate (aluminum sulfate) and start stirring it into some water.

aluminum-sulphate will turn your pink hydrangeas blue.

Add 1 Tablespoon of Aluminum Sulfate to 1 gallon (16 cups) of water and water the hydrangea. Do this once a month starting now (before the flower buds on your hydrangea start to form) and you’ll be closer to having blue hydrangeas than you were before.



I say “you’ll be closer to having blue hydrangeas” since I can’t guarantee this works because even though everything I’ve read about the subject says it will, I’ve never tried it myself.   I have every reason to believe it will work though because I read about it on the Internet.


You can try doing this with other soil acidifiers like coffee grounds or pine needles but unless you have an almost pathological addiction to coffee, chances are you won’t have enough grounds to alter your soil pH enough to make a really vibrant blue.





It’s almost guaranteed to work if your hydrangea is in a pot because you’re dealing with just a small amount of soil that you need to change the pH of, but hydrangeas in the garden are a bit harder to fiddle with. Also you’ll never be able to turn a white hydrangea blue. This only works with hydrangeas that are already pink or blue. The only thing a white hydrangea might become is tinged with pink because of the soil acidity.

This method I’m talking about here is meant for turning a pink hydrangea blue. Hopefully.

I’ve watered my hydrangeas with this solution twice now and I’ll keep doing it once a month or so until I know if it worked.

I don’t like putting things on my blog here if I don’t know for sure that they work, but if it does indeed work that’s a whole summer of blue hydrangeas I’m cheating you out of.  Now if it doesn’t work for you don’t blame me.  I warned you.  It’s not my fault.  I’m in the same boat you are, trying it to see if it’s successful.

If it doesn’t work for you, you can just hop in your pickle jar car, drive over to the King of the Internet’s house and complain. He’s usually easy to spot in his front window. He’s often seen hopping around in flaming pants, knocking lamps off of tables with his nose.




  1. Othello says:

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  2. Hanna says:

    So are you going to tell us if your aluminum sulphate worked on the hydrangeas? They MUST be in bloom by now!

    • Karen says:

      One of them is just *barely* blooming and the other plant hasn’t sent up a single flower! I’ll keep you updated, but the one that is blooming a bit seems to be blue/purple. :) ~ karen!

      • Emily says:

        How about now?!

        • Karen says:

          Ha! They didn’t bloom at all! I’ve never had that happen. I don’t think it’s related to the treatment. :) The other one got a couple of flowers and one was blue and the other one was blue on one half and rose on the other. So the experiment results will have to wait until next year I guess! ~ karen!

  3. Dina says:

    Color???? Without a “u”….. I know you don’t believe in that. Right? :)

    I think the American spell check bamboozled you. As it often does me.



  4. Amie M says:

    I wonder if anyone has tried AlSO4 on blueberries to keep their soil acidic. I’m going to buy some and find out this summer!

  5. Maureen Locke says:

    Karen, do you know if the pink and blue hydrangeas that you buy in the grocery store can be planted outside?? Are they the same as the ones you buy at a garden center?? They’re much cheaper :)

    • Pam OK says:

      I planted two hydrangeas that are considered “inside” plants on the South side of our house three years ago. They don’t grow very tall (about 16″) and only a couple of flowers, but they are pretty. They will never be bushes. We’re in Zone 4/5? in Minneapolis, MN.

  6. Margaret K. says:

    The pink- and blue-gowned fairies, Flora and Merryweather, in Disney’s Sleeping Beauty had a color-changing war over the gown they are making for Aurora. Flora wants it to be pink, of course, and Merryweather wants it to be blue.

    Thanks for the reminder, Janine! I always liked that scene.

  7. Janine says:

    Who do you think you are Karen, the good fairies from Sleeping Beauty? :)

  8. Wendy says:

    My sister lives in the north Cariboo region of British Columbia. I visited her last summer, one evening we went for a walk around the neighbourhood. I commented on all the white hydrangea people had in their yards. I told her I really liked them and thought a white one would be a nice complement for my pink hydrangea. She said I wouldn’t be able to buy one as they were either pink or blue but turned white as soon as they were planted. She didn’t know why.

    • Karen says:

      Oh. That’s odd. Well you can definitely buy white hydrangeas. There are a lot of varieties of them. :) ~ karen!

  9. Jane says:

    Turning them pink requires lime, apparently, about 1 cup of lime per year.

  10. Jane says:

    Um, this is nice and all. How do I get ’em to turn pink?

    • AggieCat says:

      Plant ’em in our soil, it and our water is naturally alkaline from all the limestone is percolates through. Argh. Not they’;d do beautifully if it wasn’t for the regular drought, and 104 degree heat all summer long. South central Texas is such a challenge to garden in. However, my tradeoff is gorgeous roses in December and January, so there’s that.

  11. Eileen says:

    Saw the note about Cleo and her teeth (and now lack thereof)…been there, done that. Also wish I’d done it the first time they told me about resorptive gum disease in cats (when I only had 4 of her teeth pulled). It’s astonishing how well they do just gumming their way through life. My girl’s only issue was one of her kibble types..they are fairly large and she had some trouble with them, so I ended up breaking each in half (yes, really!). They get mixed with another kind, so this is not “quite” as insane as it sounds…I think. Maybe you’re luckier and your Cleo eats wet food. Good healing Cleo. ChinChin says that life as a toothless kitty is just fine!

  12. Elaine says:

    When I still lived in a house, I planted a Nikko Blue in the Fall & sadly (the following year) saw the blooms turn from blue to a dirty looking pink. (I was remembering the heavenly sight of masses of blue hydrangea on Cape Cod – all those pine needles certainly helped – & wanted the same color.) I moved before trying the aluminum sulphate, however, if I still had a garden, I was going to attempt the following. I read that the a. sulphate/water mix is, naturally, difficult to “contain” around the plant as it easily disperses into the surrounding soil. So, the article suggested leaving the plant in the plastic pot but cutting off the bottom (of the pot) before planting. The sides of the pot help direct the a. sulphate/water mix to the plant’s roots while the open bottom allows the roots to still grow & spread into the soil. As I said, I never tried this but just thought I’d pass on.

  13. Erin says:

    “…an almost pathological addiction to coffee…” Check.
    Now to get the hydrangea.

  14. laura says:

    Do pennies work?

    • Lynn says:

      That’s what we used to use and they were always blue. This is the Northwest US with lots of evergreens around so maybe they would have been blue anyway……

  15. Elizabeth says:

    I haven’t done a thing other than to put them in the ground and yet, they are always a blue/purple-ish colour. Acidic rain perhaps? LOL :)

  16. Paula says:

    I’ve had blue & pink, at the same time, on my Nikko Blue Hydragea before. That was kind of cool, but I like the blue better.

  17. ronda says:

    ah yes, British spelling and pronunciation. Cuz then there’s elasticated. But that’s a whole other subject.
    Back to hydrangeas … have been wanting to plant some for years, and now that we’re working on our back yard this year, I will definitely be planting some. Don’t care what colour they are! Just want some!

  18. Leisa says:

    Read your newsletter about this on the Lee Valley site – still have the Crystal Gale song stuck in my head! ?

    • NinaMargoJune says:

      Was wondering what today’s ear worm was going to be. Now I know! “Donuts Make My Brown Eyes Blue”….

    • Karen says:

      I’ve been singing that song since then! I mean all day in my head and sometimes out loud. I CANNOT get rid of it, lol. ~ karen!

    • Jan in Waterdown says:

      Thank you for posting that Leisa! I thought I was going nuts since it all seemed soooo familiar! Actually, truth be told, I thought Karen! was going nuts, doing the same thing twice. Hmmmm . . . maybe I shouldn’t have admitted that . . . whatever lol! Getting old(er) has it’s benefits since I don’t care about stuff so much any more. Have a grand day y’all, it’s a gorgeous one here in southern Ontario!

  19. Marlene says:

    In South Africa, we also get awesome hydrangeas. You can often see both the pink and the blue in the same garden – we take pride in our hydrangeas! :-)
    In my experience, both of the following also work to make them blue, if you are in a place where you cannot get aluminium sulphate (yes, we spell it that way). (Yes, I meant both words).

    1 – put used batteries in the soil around the plant. Also heard this is not environmentally sound, even though it works, so…
    2 – have the males of the household pee around the base of the plant. Very useful if the plants are hidden from public view, trickier to get away with otherwise. Yucky, true. But very effective, and least effort.

  20. Paula says:

    I tried this for a couple years but it didn’t work for me, perhaps I should add the coffee grounds, too and keep at it. Either that or dig it up and stick it in a a pot.

  21. Amy Campion says:

    Technically, it’s the aluminum that turns the flowers blue, but plants can’t take up aluminum (which is naturally present in most soils) very well if the pH is too high. Aluminum sulfate does lower the pH faster than sulfur alone, however, and using it guarantees that there will be aluminum for the plant to take up when it is able to.

  22. Milton says:

    Have been using aluminum sulfate for a row of hydrangeas my wife planted along a shady driveway almost twenty years now. Each plant is about 3 feet in diameter and I use a pound sprinkled around the drip line of the plant and worked into the soil along with compost and slow release fertilizer. All the hydrangeas are always a solid beautiful blue color. Mixing and applying with water is a whole lot of work. Hydrangeas do need a lot of water but I had to put in a drip irrigation system to take care of that as well. Some years are better than others for yield here in Mississippi but, in a banner year, they are spectacular. I’m sure yours will be as well to decorate your lovely house.

  23. Bobbles says:

    Every. Single. Day. Of. The. Year my dad patted his coffee grounds into the soil around his hydrangeas. And every year they were deep blue. He died in 2007 and I was just noticing the buds look like they’ll be pink again this year. I wish he’d come back, I’ll even make the coffee!

    • Elizabeth says:

      Hugs just because xo

    • Karen says:

      :( Well. It’s time for you to start back with the tradition. ~ karen!

    • Mary W says:

      My grandmother made tons of iced tea (for 7 kids and their friends) every day and every single day, the used tea leaves went onto her hydrangeas which were always beautiful with no other work involved. BUT, I think consistency is the key and the every single day thing is what mattered. If you or I are normal (who is?) then Karen’s tip will probably work and even better since I’m NOT consistent with anything. She died in the sixties and I miss her and her hydrangeas, too.

  24. mia pratt says:

    Ok so this has nothing to do with the acidity of soil; it’s more about the symbiosis of our “special relationship” as blogger and blogee. I’ve been working on a painting that has deep blue hydrangeas in it, and despite hours on google and scanning multiple image sites, I just couldn’t find a good close-up that showed the perfect blue hydrangea bloom I could use for reference. Well, skip to right now, Sunday night in bed with my dog and a few mint Oreos (ok six) on Sunday night and I’m thinking, geez, now I gotta search for photos of those reclusive deep blue hydrangeas again for tomorrow’s work. And then ZING, like dangling a shiny pretty thing in front of a kitten, your blog post arrives in my inbox and I forget about everything else (even though it no longer says Whoopeee which I just loved…sigh). Of course I opened it up right away, and dear Scrod in Leaven – there’s the exact, perfect photo I’ve been searching for…gift wrapped, high-resolution, detail photo of a hydrangea bloom in the exact color I need. So who says there’s no such thing as kismet, karma, miracles? Now I can just lay contentedly in bed with my dog and our mint Oreos (ok, there were eight!), no search necessary – knowing that tomorrow morning, I will be painting my blue hydrangeas<:}

  25. TucsonPatty says:

    I also have heard of this, but don’t have any hydrangeas to try this method. I have a yellow rose bush from my folks farm which my brother swears that when my mom transplanted it to a new location, the same bush became a pink rose. I think he is full of it, and she must have gotten a new bush. Others have told me stories of soil acidity etc., and some have suggested the yellow might have been grafted onto a bush that was originally pink. My roses are pink now and are from that second bush. Inquiring minds want to know – and I’m anxious to see your experimant results. Keep us posted on colors!!

    • Julie says:

      Sometimes you have a rosebush that is grafted (which tea roses usually are) onto the roots of a hardier rose. If the top of the plant is damaged, sometimes the top will die, but you will get regrowth from the hardier roots. Bet that’s what happened!

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