Hydrangea Color: Not Getting Purple or Blue Hydrangeas Anymore? How to Change Hydrangea Color


[Color changing hydrangea… on it’s way to fully pink.]

If you’re like me, you gleefully bought blue hydrangeas from the nursery and a year or two later found that the blooms’ color changed from blue to pink.  Your soil pH (a pH of 6. or above, usually a poorly draining, clayey-type of soil) is the cause.

So how do you get back blue hydrangea flowers?  Basically: lower the soil pH, and you’ll get the blue back.

Go to the nursery or big box hardware store, buy a soil pH kit and test your soil so you know what you’re working with.  You’re going to need to create and maintain a pH of 6.5 or lower to see blue hydrangea blooms.  A general rule to lower soil pH is to add sulfur; but in particular, aluminum sulfate has been proven to work the best in changing hydrangea color from pink to blue. (Ditch that myth about burying a rusty nail next to your plant; it’s  not going to give you results, and it is just not smart to add a such an unfriendly thing to an area where unwitting people or pets may be harmed if they encounter the nail.)

Try to isolate the soil, grow in pots or a raised bed;  using good quality potting soil, and lots of compost.  One alternative to adding alum is to add copious amount of organic matter to amend your soil. The best method for this is to create raised beds with a good quality topsoil and then to consistently amend the soil with A LOT of compost.  Adding organic matter helps lower the pH, and if you have clay soil like I do, compost has the added benefit of helping with drainage; it also helps lessen the need to fertilize.  You will not typically need to fertilize as much (if at all)
because the compost helps plants unlock the nutrients in rich clay soil.  If you are still struggling to get blue flowers, try adding alum. But before adding it, be sure you get that soil pH kit from the nursery and test your soil.   You need to know what you’re working with and have a goal. Adding too much aluminum sulfate (or alum) can be lethal and could decimate your plant, especially if it is not yet established.  Consult with a nursery professional or horticulturist if you need help figuring out how much to use for your growing situation.  Below, I tell you what worked for me.

My experience: I’ve tried changing the color two ways with plants in ground and in pots.  By far, pots were easier to maintain, and had more consistent color results.  In ground, I started with a soil pH of about 8.5 and it took about two seasons of mending to get the the pH to 6.0 using a boat load of compost.  Flower colors were varied, not uniform.  In pots, I started with a good quality potting soil, lots of compost, and added a weak solution of aluminum sulfate just before the plants begun blooming.  Soon after I saw buds, I applied another solution of alum and within one growing season, I had flowers that were turning from pink to blue:  by the next season the pot growing hydrangeas in pots were a uniform blue.  (Over the years, I’ve stopped fighting nature and let the blossoms go back to pink. Seems I’ve converted: it’s best to accept pink flowers and just let nature do its thing.)

Applying Aluminum Sulfate
Generally, you can apply aluminum sulfate once or twice during the blooming season.  Once early in spring, when you see
flower buds, but before buds break; and then again, in late summer if your cultivar is a repeat bloomer.

  1. Water your plants very well before adding alum.
  2. Thoroughly mix (dissolve) 1TB of aluminum sulphate (alum) in one gallon of water.  (Tip: use an old one gallon orange juice, milk or tea bottle so you can really shake the solution.) A one gallon solution should be enough for a mature hydrangea bush.
  3. Carefully apply your mixture to the soil at the base of the bush.  I’m not sure about any negative effects on nearby bushes, mine were planted next to coleanema and boxwood, and I saw no visible effects.  If you have a smaller, less mature bush, try a solution made from 4 cups of water to 1 teaspoon of alum.

How long will this last?
Keeping the flowers blue will depend on your situation and strength of will.  The easiest route is to grow your hydrangea plants in containers or in a raised bed. The rougher route is to leave them in the ground because you have less control over what influences your soil.  Considering that adding alum may overtime build-up to toxic levels, I wouldn’t choose it as a long-term solution.  I used it for a couple of seasons and then
eventually let nature take its course.   For the last two years, I’ve had mostly pink hydrangeas, and I’m getting used to them.

Final Words:
If you’re the contemplative kind, you might want to consider the motivation behind why you want blue colored hydrangeas and why you are going to fight nature.  Do you have something to prove about your gardening skills?  Do your neighbors only have pink and you want to be the one with blue, are you doing this because you want the rarity of the blue in your area? Or, is it for nostalgic reasons– perhaps you grew up around blue hydrangeas and can’t stand that the reality of your pink ones clashing with memories…   If you decide to use the aluminum sulfate solution, you may want to reconsider why you’d want to create bad soil by adding salt to it (essentially what you’re doing).  And, you may, like me, decide it’s not worth the the sustained effort and damage.

Protected by Copyscape Online Plagiarism Check

This entry was posted on 232319H Jul 2010 and is filed under hydrangea. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

Leave a Reply