Hardy Hydrangeas



Pink Diamond Hydrangea

Hydrangeas are great flowering shrubs, if you choose the right variety for your growing conditions.  If not, both you and the hydrangea could be in for life of misery.  There are two species that do well in zones 3 and 4:  Hydrangea arborescens and Hydrangea paniculata. 

A lot of Hydrangea macrophylla or "big leaf hydrangeas" are marketed as hardy to zone 4, but in truth, they are really only reliably bloom hardy to zone 5.  These are the Endless Summer, Forever and Ever, and similar cultivars.  These lines are bred in Minnesota, which seems like it should be close enough to North Dakota to make it work here.  But, we get just enough colder actual temps that these don't always bloom well for us.  The big leaf hydrangeas are those that have the large "mophead" flowers that change color depending on the pH of the soil.  We see these in the garden centers covered with beautiful flowers, usually blue because everyone wants a blue flower.  We take them home and plant them and after the flowers we bought are spent, we never see the same plant again.  Most big leaf hydrangeas marketed for northern climates bloom on a combination of old and new wood and they set their buds on the old wood the summer before they actually bloom.  The problem is that these buds are very sensitive to extreme cold and often freeze off, unless they are heavily mulched.  In the spring, the plant will begin to grow new wood and you'll likely end up trimming the old wood off because of winter kill.  Later in the summer, you might get a few blooms on the new wood, but it won't likely won't produce like it did when it was raised in those perfect nursery conditions before it came to live with you.  In just the right spot, and with just the right growing conditions, you might have luck with the big leaf hydrangeas in zone 4.  But, then there's that rule about a plant not requiring more care than your children...

You can have beautiful hydrangeas without all the work and worry that I've found to be associated with the big leaf varieties.  Hydrangea arborescens or the smooth leaf hydrangeas are some of the hardiest, doing well even into zone 3.  There are varieties that grow from three to five feet tall and bloom reliably and profusely from June through September.  The flowers are round and come in a cream color.  The flowers stay on the stems and dry to a tan that will stay on the shrub throughout the winter.  They can also be cut and used in dry flower arrangements.  "Annabelle" is the most common cultivar and is seen in many yards throughout the northern part of the United States.  "Radiata" is very similar in growth to "Annabelle" but has a lacier appearing flower cluster.  Characteristic of these shrubs are the huge, heavy flowers that actually weigh the stems down, giving the entire shrub a weeping or draping effect. 

Hydrangea paniculata blooms later than h. arborescens, generally beginning its bloom season in July, but then persisting throughout the fall.  This species has large cone-shaped flowers that will also dry and stay on the stems throughout the winter.  There are over 30 cultivars of h. paniculata rated for zone 4 or colder. 

The oldest and most common is the "Peegee", also known as "Grandiflora".  Peegee blooms a little later, generally beginning towards the end of July or early August in my garden.  The blossoms open with  a greenish-white color, but progress from this to a creamy white to a pink tinge as they age.  These conical flowers can be as long a foot each on mature, well-established shrubs.

"Pink Diamond" is another cultivar that is reliably hardy and a good bloom producer for me.  The petals have a lacier look than those of Peegee, opening the greenish white but age through to a beautiful rich "diamond dusted" pink.

"Limelight" is another great producer in the Wiese Acres gardens.  It is a very hardy shrub that lives in a location that receives almost full sun without getting sunburned or wilting in the heat of day.  It produces dramatic cones of creamy yellow- green tinged flowers that stay that color until they are quite mature, when they turn to a more pinkish color.  Limelight grows to about six feet tall and four to six feet wide.  "Little Limelight", also sometimes marketed as "Little Lime"  has similar habits but stays a much smaller three to four feet.

"Pinky Winky" is a descendant of "Pink Diamond" but has bi-colored pink and white flowers that are held on strong stems so they stay upright, even with a full sized flower.  It is a tough, reliable bloomer and has a deeper green foliage for a striking contrast with its two-toned flowers.

"Little Lamb" is a cultivar that is marketed as a "compact" shrub.  That may be just a bit deceiving.  Little Lamb can grow to six feet tall, but generally stays within about four feet spread.  What is compact about it is the flower clusters.  Each flower is smaller, making for a much denser and more compact appearing umbel.

"Quick Fire" is a nice addition because it blooms a full month earlier than most of the other paniculatas and then blooms right through fall with white flowers that turn to a deep rose as they age.    "Invincibelle Spirit" blooms all season long with a large, deep pink blossom.  "Incrediball" is similar to Annabelle in growth but sports even larger blossoms.

One relatively new variety I tried last year is "Vanilla Strawberry" which is supposed to produce three colored blossoms of white, pink and rose through much of the summer.  The jury is still out on this one.  In spite of adequate moisture and protection from hot afternoon sun, I'd come home to find it severely wilted just about everyday.  I'm going to give it a chance to clean up its act this year, but if it doesn't do better, I think it will not be a long term addition to Wiese Acres. 

There are many other cultivars of h. paniculata and most of them are worth a try in your garden, if you have space.

Thursday, I'll discuss care of hydrangeas to give you the best results in your northern gardens.