Hydrangeas:
Turning Blue and Pruning
Q: How can I turn my Hydrangea blue? I am hoping it is something
that I would have on hand.
A: If you're growing Hydrangea Marcrophylla (French Hydrangea)
you can turn it from pink to blue by lowering the pH level of
your soil. The color is determined by the amount of aluminum available
to the plant. Add 3 to 4 tablespoons of aluminum sulfate to a
gallon of water. Apply it 2 times, 2 weeks apart, for 4 to 6 months
prior to blooming. You can also add coffee grounds, eggshells
or ground-up citrus peel to the soil. You're shooting for a pH
of 5-6.
On a similar note, blue hydrangeas can be changed to pink by adding
3-8 cups (depending on the size of the plant) of dolomic lime
around the base of the hydrangea. Do this 2 or 3 times between
the blooming seasons. As an alternative, you can also try a bit
of superphosphate around the base of the plant. Shoot for a pH
of 6.8-7.2.
The color change doesn't happen overnight so be patient. It can
take as long as a year or two to see the results. The white varieties
of hydrangeas (such as PeeGee, Silver Leaf, Hills of Snow, etc.)
cannot be changed. They remain while regardless of tampering with
the pH of the soil.
Q: I planted a nikko blue hydrangea 2 years ago but it has never
bloomed. I fertilize it and it is in a sunny location (6 hours
of sun). It is healthy looking and green but no flowers. What
can be wrong?
A: Your hydrangea sounds like it's getting the right amount of
shade/sun, so as long as you're not using a fertilizer that is
too high in nitrogen, the problem is probably your Nova Scotia
winters. Cold damage is the most common reason this type of hydrangea
fails to bloom. You didn't mention whether or not you cover your
Nikko in the winter. Although they are usually rated to zone 4
or 5, Nikkos (especially when young) should be given winter protection.
You can do this by surrounding the shrub with a cage made from
chicken wire and filling it up with leaves or straw. The Nikko
Blue blooms on old wood so pruning it can also be tricky. Flower
buds usually form on the stems sometime between August and October,
so most gardeners prune them by the end of July. Later pruning
puts you at risk for cutting off next year's buds. Fortunately,
if Nikkos are located in a fairly protected area, pruning usually
isn't necessary for this type of hydrangea unless you need to
rein them in or revitalize them. Dead stems can be removed anytime.
To determine when to prune, you will need to determine what type
of hydrangea you have. Hydrangea either blooms on "old"
wood or "new" wood. Ask neighbors or a nearby nursery
to help you with identification. Hydrangea that blooms on old
wood (Macrophylla (“moptops”), oakleaf, and lace caps)
should be pruned only after they bloom in the summer, before August
to be safe, because next year's buds form on this year's growth.
Hydrangea that blooms on new growth (Annabelle, Limelight, Pee
Gee, and other H.paniculata varieties) can be pruned to within
6-12 inches from the ground in the early spring. No matter which
type you have, you can begin to reinvigorate plants by cutting
1/3 of the branches to the ground in the summer.
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