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On gardening: Oakleaf hydrangea tops for long lasting fall color

December 15, 2014

The large fiery leaves of the oakleaf hydrangea are the perfect complement for the fine textured needle-like foliage of the spreading yew.

The past couple of weeks one of my LinkedIn groups has been discussing the best shrubs for fall color. In our garden it was no contest-the oakleaf hydrangeas won this challenge in blazing fashion.

Whether it is trees or shrubs we look at fall color scientifically. Words like carotenoids, pigments and chlorophyll enter into the discussion, as does auxin, gibberellins, other growth hormones and enzymes. It is enough to get the heart racing!

To simplify, conditions to make great fall colors boil down to cool night temperatures and warm, sunny days. Climatic conditions have the greatest effect on the production of anthocyanin pigments that intensify the red and scarlet colors. Conditions that most favor these colors are sunny days and nighttime temperatures between 45 degrees and freezing. Even though we have had a couple of record lows in Savannah this fall has-been just about perfect.

Though chlorophyll in leaves decline in the fall, it is still important for photosynthesis to take place. If an abundance of cloudy weather prevents photosynthesis from occurring, leaf color will be mediocre even if temperatures are ideal. This also can weaken the leaf, making it easy for a northern wind to blow it off.

Cool night temperatures limit the movement of sugar from the leaves. It also reduces the rate of respiration in the leaf, so some sugars are converted to carbon dioxide. Those retained are converted to colorful anthocyanin pigments. So in addition to our oakleaf hydrangeas showing great fall color so did our Chinese pistache, Oliverís Taiwanese maple, Florida maple, and sawtooth oak.

The oakleaf hydrangea is native from the Gulf Coast as far north as the Tennessee/Kentucky border, but donít be disturbed. It is recommended for zones 5-9, meaning that even parts of Michigan and Maine can relish in both the glistening white blossoms as well as the burgundy red foliage.

To grow yours select a site in partial shade. Keep in mind that these are large shrubs reaching 6 to 8 feet in height with an equal spread. Our oldest ones are approaching 10 feet.

Prepare a bed for your hydrangeas and companion plants by incorporating 3 to 4 inches of organic matter and 2 pounds of a 5-10-5 fertilizer per 100 square feet of planting area, tilling deeply. Dig the planting hole two to three times as wide as the rootball but no deeper. The wide hole allows for the quickest root-expansion and acclimation into your garden.

When it comes to fall color the oakleaf hydrangea is superior for another important trait and that is the length of leaf retention. In other words the leaves donít just turn red and then fall off a week later. They last and last often persisting well into winter.

The oakleaf hydrangea screams to be planted in a woodland border where it can be combined with ferns, hostas, and colorful French or mophead type hydrangeas. In the south they should be combined with late blooming azaleas like those from the Satsuki group which bloom in May. When choosing fall companions however, this takes a little extra thought.

My favorite combination planting in our garden features the large colorful burgundy leaves with the fine textured needle-like foliage of the spreading yew. This is terrific complementary partnership playing off the contrast both in texture and color.

There will be several oakleaf hydrangea varieties at your garden center next spring. Snow Queen may be the most famous for its upright habit and large blooms that hold up well after rain. Look also for the US National Arboretum released Ruby Slippers that is somewhat shorter and more compact. The flowers start off white, age to pink and finish to a deep rose. Its fall leaf color is considered to be superior.

Fall color is something most often relegated to tree selection but shrubs like the native oakleaf hydrangea can add their own fiery blast as well.

 

 


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