Aluminum Sulphate To Blue Up Hydrangeas

Hydrangea 'Endless Summer':
Acidifying Hydrangeas

Apparently where pH is low, people want to pink up their blue Hydrangeas.  Here where pH is high, naturally we want to blue up our pink Hydrangeas.  Perhaps we should just switch gardens periodically according to our hydrangea desires.  But rather than going to all that trouble, I tried the recommended Aluminum sulphate to blue up my pink-flowering Hydrangeas.  Here are my results:

Acidifying Hydrangeas

Yes, aluminum sulphate works, but like the old joke about voting, you have to do it early and often:  at least once a month, before and during bud formation.   I followed package directions, which meant two tablespoons in a gallon of water.  I had to agitate the water a while to get the aluminium sulphate to dissolve.   I gave my 30"x30" 'Endless Summer' hydrangea two treatments, on the first of April and the first of May.  This wasn't quite enough.  The first blooms to form are fairly pink, the following are fairly lavender, and the last, just beginning to open lately, are finally a fine sky blue.  So next year, I'll start on the first of March, or even February, and give 3 or 4 treatments.   Last year the plant was smaller and I think I started earlier, so the blueness was  better. 

My variegated lace cap hydrangea blued up with just one treatment--that and the 'Shooting Stars' variety seem easier to influence than 'Endless Summer'.  'Ayesha' and 'Miss Minnie Penny' remain stubbornly pink. 

Incidentally I should mention that Hydrangea 'Shooting Stars' wins my vote for Best Plant You Can Buy At Trader Joe's.  Their succulents are a little pricey, in my opinion.  Their orchids are good but I don't buy orchids any more.  The potted mini roses--I don't buy those either.   Their blooming bulbs are not a good value (are blooming bulbs ever a good value?).   Their florist hydrangeas are ok, but with the introduction of 'Endless Summer' and other reblooming varieties--why bother?  But 'Shooting Stars' has been a gem.  Beautiful plant, and now growing happily in my garden.  And it was something like $6.99--cheaper than you can get a hydrangea at a big box store.  So watch for that one. 

Hydrangea 'Shooting Stars'
Hydrangea 'Shooting Stars'

So to close out this post, remember to be cautious with aluminum sulfate--too much can kill the plant.  Another approach is to apply soil sulphur, which I bought in the form of little yellow aspirin-like pellets.  Supposedly this takes longer, but is less dangerous, and just as effective.  I started applying soil sulphur to my blueberry plants, which are real acid soil lovers, and yes, they loved it.  More and healthier foliage was the result there.    Aluminum sulphate or soil sulphur--either way, easier than moving to Georgia.

Hydrangea 'Endless Summer':
Endless Summer Hydrangea Update May 29, 2012  I've switched from Aluminium sulphate to soil sulpher.  Soil sulphur needs less applications per year (once in late winter/early spring, once as the winter rains begin in November or December), which for a lazy gardener like myself is a plus.  It also seems more effective, and without the toxic effects that too much aluminum can produce.  I vote for soil sulphur.
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Comments

  1. I have had the same result in trying to "blue up" my hydrangeas, although they were a bit more purple than these. I finally conceded and my 'blue and white' garden became 'blue and white and a little bit of pink' garden!

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  2. Personally, I think a hydrangea is at it's most beautiful when it is mixed like the photo above. I love the blue and I love the pink but the mixed colors make my heart soar!!

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  3. Kids Matter you are quite right. I get so besotted with blue I forget that a hydrangea with mixed colors is a perfectly beautiful thing.

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