Gardening: Pick hydrangeas suited to Inland Northwest climates

On the west side of the Cascades, hydrangeas grow to the size of small trees, and in a couple of weeks they will be covered with huge blue flowers that will last well into late summer. While gardeners in the Inland Northwest will never be able to compete with our coastal counterparts, we certainly can grow our fair share of hydrangeas – if we manage them carefully and pick the right varieties.

Unfortunately, the luscious blue or big leaf hydrangeas (Hydrangea macrophylla) that grow to perfection on the coast struggle here in the Inland Northwest for several reasons.

First, the plants need acidic soil to produce clear blue flowers. Our soils and water tend to be on the alkaline side so we end up with either a mixture of blue and pink or just straight pink flowers. While we can add aluminum sulfate to the soil to lower the acidity, we can’t easily change the pH of the water we irrigate with. And they need a lot of water.

Secondly, the big leaf hydrangeas are close to their hardiness limits here. The plants are hardy to USDA Zone 5 but the flower buds that overwinter on old wood are only hardy to Zone 6. The buds are easily killed in a cold snap that otherwise doesn’t affect the plant. Because of the mild winter we had this year, I suspect some gardeners who have plants in protected spots might see a pretty decent bloom this year, albeit in pink.

Lastly, the plant needs a steady supply of moisture to do well. Before the deer put me out of the hydrangea business, it was always the first plant in the garden to wilt. It also needs some shade in the afternoon.

But take heart. While the big leaf hydrangea may be a challenge to grow here, there are several other types of hydrangeas that do well here. The PeeGee hydrangea (Hydrangea paniculata “Grandiflora”) is hardy to Zone 3 and produces buds on this year’s wood so it isn’t affected by winter cold. The plant produces creamy white flowers in late August that, over a few weeks, age to a light dusty pink. It is a vigorous grower that needs evenly moist soil and some afternoon shade.

Another great hydrangea hardy to Zone 3 is the Annabelle or snowball hydrangea (Hydrangea arborescens “Annabelle”). It produces huge white blooms in June and July that can reach 8 inches in diameter and resemble – what else – giant snowballs. Like the PeeGee hydrangea, the Anabelle produces buds on this year’s wood and can grow to a respectable 4 to 5 feet tall and 3 to 4 feet wide. Because the flowers bloom on new wood, it can be pruned hard in very early spring. Give it an even moisture supply and afternoon shade.

In addition to water and shade, hydrangeas need well-drained soil rich in organic matter. They also benefit from a 2- to 3-inch layer of mulch to retain soil moisture.

Pat Munts is the co-author, with Susan Mulvihill, of the “Northwest Gardener’s Handbook.” Munts can be reached at pat@inlandnw gardening.com.