How Do You Keep Bigleaf Hydrangea Flowers Blue?

“What’s the best way to ensure that my blue [bigleaf] hydrangea stays blue?” Question from Gaye of Saint Peters, Missouri

Answer: It all has to do with soil pH. There are two hydrangeas that have flowers whose color changes depending on whether the soil is acidic (3.5-6.8), alkaline (7.2-10), or neutral ( around 7). These are bigleaf hydrangeas (Hydrangea macrophylla, Zones 5-11) and Japanese mountain hydrangeas (Hydrangea serrata, Zones 6-9). If your flowers are on the pinker side then your soil is more alkaline, and if they are erring towards purple then your soil is more neutral. To achieve flowers with a bluer hue, you will need to lower your soil pH. There are several ways to do this.

Steps For Acidifying Soil

Black Gold Peat Moss is naturally acid, so you can amend the soil around your hydrangeas with peat to lower the pH. Follow up by adding an acidifying fertilizer supplement. Many reputable fertilizer companies make “acidifying fertilizers” or soil acidifiers–any would do. (Please click here for more information about how to acidify your soil from Oregon State University.)

Just lower your soil a little below neutral, and those hydrangeas will begin to turn blue!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

Pistachio Hydrangea is the Winner

Hydrangea 'Pistachio' - Mike Darcy
At the recent Farwest Show (national nursery trade show held in Portland, Oregon), there was a section call “New Varieties Showcase”. New and recently introduced plants were exhibited and participants were given ballots and asked to vote for their favorite plant. The People’s Choice Award was given to Hydrangea macrophylla ‘Horwack’ Pistachio. Commonly known at the Pistachio Hydrangea, this Hydrangea has flowers that are scarlet-red and green with violet centers. The flower color changes as the bloom ages which makes a very visual interesting feature. The plant tends to be a compact grower and likes a well drained soil. To avoid summer burning of leaves and flowers, give it some protection from the hot afternoon sun and plant in a well drained soil. Black Gold Garden Compost Blend is a good amendment to maximize your soil’s potential. This would make an excellent container plant for a deck or patio.