July 9, 2011 in Washington Voices

Some hydrangeas do swell here but big leaf varieties not reliable

Pat Munts
 
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Blue or pink?

The skinny on color changes in hydrangeas:

We tend to see pinkish colored flowers on Hydrangea macrophylla in the Inland Northwest because of our neutral to slightly alkaline soil pH. Acidic soils will generate blue flowers. It is possible but not easy to change the pink flowers to blue by working aluminum sulfate into the soil around the plant early in the spring every year.

Tried to grow big leaf hydrangeas in the Inland Northwest but never get the big, bold, blue flowers to appear? You are not alone.

If you have seen the big leaf hydrangea (Hydrangea macrophylla) on the coast or in the South, you know its enormous blue or pink flowers are hard to resist. Sadly, the big leaf hydrangeas aren’t reliable bloomers here because they are at their hardiness limit.

The plants are hardy to USDA Zone 5b (minus 10 to minus 15 degrees), but the flower buds are only hardy to about zero to minus 5 degrees. That means the plants may do fine but the overwintering flower buds that grew the prior summer are easily killed by our average winter temperatures.

Two recent introductions, Endless Summer and All Summer Beauty, were supposed to get around this problem but haven’t lived up to their marketing. Both plants bloom on wood that grows in the same year thus avoiding the winter temperature issue. The challenge is that by the time the plants have grown enough wood to bloom, we are at the end of the growing season and they don’t put on as much of a show.

There are options if you like the big, bold flowers that come only in white or pale green.

The PeeGee hydrangea or Grandiflora (Hydrangea paniculata) is hardy to Zone 3. Its flowers are conical in shape and open in late August as a creamy white that ages to a light pink over several weeks. The Annabelle or snowball hydrangea (Hydrangea arborescens) has huge white blooms in June and July that can reach 8 inches across. Both grow to at least 4 to 5 feet tall and 3 to 4 feet wide.

Lastly, if you are looking for a robust vine for a shady place, consider the climbing hydrangea (Hydrangea anomala petiolaris). This stout woody vine is hardy to Zone 5 with glossy, bright green leaves and creamy white flowers in June and July. The plant takes a few years to establish its roots before it climbs up any stout arbor, wall, tree or other structure that can support its clinging rootlets and weight. Its gnarly trunks and branches add winter interest to the garden.

All hydrangeas need to be planted in a sheltered location away from winter winds. They need well-drained soil, regular watering and some protection from the afternoon sun in the summer.

Master Gardener Pat Munts can be reached by email at pat@inlandnw gardening.com.


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