Four ways to make your hydrangeas blue

Hydrangeas are a Cape Cod icon, and for most people, the bluer they are, the better. Personally, I enjoy the multicolored look, above- it’s like a big, colorful, hydrangea party. But if blue is for you, here’s what to do:(Kinda sounding like Dr.Seuss here.)

  1. When planting hydrangeas, take the time and effort to prepare the bed properly. This is much easier and more effective than trying to correct the problem after planting. Fill the bed with rich compost and loam, and mix in lots of leaf mold or peat moss. (I prefer leaf mold because it is more sustainable, but it is not always available.) To prevent wilting and fading of flower color, Locate the bed where the plants will get morning sun and be shaded in the afternoon. Dig the bed down into the earth, rather than mounding it up. This will catch and hold the available water, and hydrangeas love water. Feed hydrangeas with Holly-tone® 4-3-4 at planting time, and yearly in the spring. Mulch with pine straw, if possible. This will acidify the soil as it breaks down. The ideal soil ph for blue hydrangeas is 5.2-5.5.
  2. OK, so it’s not a perfect world. Your hydrangeas are already planted, and your soil ph is hovering around 7.0. You have a much more difficult task ahead of you, and results can be iffy.  Feed your plants with Holly-tone® 4-3-4 once a year in Spring when new growth begins to emerge. Add Aluminum Sulphate to soil a week or two later. Aluminum will make flowers blue, and Sulfur will lower the ph of the soil to make the aluminum available to plants.
  3. Top dress soil with leaf mold or peat moss, and mulch with pine straw. Pine bark breaks down more slowly, but it is a good alternative mulch.
  4. Be aware that lime can leach from surrounding areas to hydrangea beds. Lime in foundations, on lawns, and in shell driveways can raise your soil PH and turn your hydrangeas purple or pink. Despite your best efforts, you may not get the results you want with established plantings.


About villagegardener

Cindy Hollett is a Massachusetts Certified Horticulturist, Estate Gardener and Garden Designer, living and working on Cape Cod.
This entry was posted in Gardening, Plant Care and tagged , , , , , , . Bookmark the permalink.

4 Responses to Four ways to make your hydrangeas blue

  1. Thank you, this is awesome! I love my Hydrangeas to be the deepest blue they can be-but afraid to treat them- I’ll either do to much or too little of something and hurt them. How much Aliuminum Sulfate should I use per plant?

    • Thanks for your interest! A general rule of thumb is to use 1 pound of aluminum sulphate for every 3 feet of the shrub’s height, and work it into the soil around the base of the plant (below mulch) well.

  2. Pingback: Hydrangea, the colour-changing flower | Grower Direct Fresh Cut Flowers Presents…

  3. Pingback: GOTTA LOVE HYDRANGEAS! « JahsWorld

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