How to Make a Snowball Bush Blue

Some people call big-leaf hydrangeas "snowball bushes," because of their big, round clusters of tiny flowers, but in horticultural circles, the name "snowball bushes" is reserved for snowball viburnums. Most big-leaf hydrangea varieties can produce either pink or blue “snowballs.” Flower color depends on several factors, including a cultivar’s color capacity. Also critical are soil aluminum levels, which affect pigment production. In soils with a pH of 5.0 to 5.5, flowers will be blue. Where pH is higher than 6.0, blooms are pink. If soil pH is between 5.6 and 5.9, you’ll get intermediate lavender and other intermediate color tones.

Aluminum sulfate

Instructions

- 1
  Apply aluminum sulfate, which adds aluminum and acidifies soil, or lowers pH. Start whenever you wish during the growing season. The color change won’t occur until the following season at the earliest.
- 2
  Dissolve aluminum sulfate in water and use that to irrigate your snowball hydrangea bush, saturating the entire root area.
- 3
  Use 1 oz. of aluminum sulfate per gallon of water, or 2 oz. in 2 gallons of water for a large shrub, every time you water. It’s easy to overdo it with aluminum sulfate.
- 4
  Continue to water with aluminum sulfate solution the following year, and monitor flower color.
- 5
  Cut back to monthly applications of aluminum sulfate when your snowball hydrangea is producing flowers close to the color you prefer, to maintain soil pH. This color maintenance system is imprecise, so adjust the sulfate-water schedule as needed.

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