I've never done it but heard to use alum. sulphate. Not sure of the amt or how often to water with it.
I read that it can burn the roots....
What is your experience with this?
Finally a nice day..but WINDY!!
I tablespoon of aluminum sulphate in one Gallon of water...make sure all the crystals are dissolved...
before the alum. sulphate application, make sure you water the hydrangea plant well..it is ok if it is dripping wet..
pour the al. sulphate solution right at the base of the plant, do not let any of the solution to touch the foliage or the leaves will get burn spots..
one gallon solution is enough for a mature hydrangea plant (3' X 3')..
let the solution sit in the soil for an hr and water the plant lightly and briefly to wash off any extra solution sitting in the soil that could burn the roots...
you should not apply the solution more than once every two weeks...you can apply two applications in a month and not risking to kill the plant...much more often than that, i dont know, but i won't reco it..
btw - the pink blooms already blooming now WILL NOT chg to blue even after the al. suphate solution..
the sulphates will make the soil more acidic and future bloom colors will chg accordingly..
so if you have a rebloomer like endless summer now and it is beginning to show the pink blooms, the sulphate application will not chg the pink blooms now..but the new blooms later in the season will chg to blue if the pH is low enough//
if you dont have a rebloomer and all the buds are set already, an al. sulphate application would not chg the color for the blooms this season..
for me - I don't do al. sulphate applications much because it does poison the soil to a certain degree - if you have a Rhodi or Azalea nearby, they may not appreciate the extra aluminum in the soil...whenever I do the sulphate application, i do one in spring - when the flowerbuds are forming - april in that case...and another one in July for the later blooms...twice is enough for me to keep my endless summer to bloom in a brilliant blue color...
It is important to know the cultivar you are working with as well. Not all macrophyllas will readily or easily change colors......some pinks are very stable and will remain pink regardless of soil pH, or at the very least a mauvey-purple. It is not always possible to make a pink hydrangea blue :-)
Aluminum sulfate, aka hydrangea bluing, is not exactly a magic elixir for hydrangea color and will not necessarily force the hydrangea to change color (if it is inclined to) if the soil conditions are not right. Blue flowered hydrangeas need acidic soil to remain blue and depending on existing pH, just adding Al2(SO4)3 to the soil in approved amounts to avoid aluminum toxicity may not be sufficient to properly lower the pH to effect a color change. If it does, the change will not be permanent and you will have to repeat applications with each season. And then there is the issue of the pH of the irrigation water as well.