Sunday, December 4, 2016

Parking Lot Maples

It’s been a good year for maple trees in terms of fall color, and their widespread use as a parking lot tree has made that very noticeable this year. Some of you might be noticing these trees for the first time, and might be considering one for home use, so let’s talk about what these are.

Twenty to thirty years ago, we saw the widespread use of ornamental pears (Pyrus calleryana ‘Bradford’) in parking lots, professional landscapes and the yards of new homes. Eventually, people realized that those pears were prone to breaking, had smelly flowers, and were even becoming invasive plants. Landscapers searched for replacement trees, especially in parking lots where trees have to tolerate tough conditions.

I’ve written before about the many types of oaks used as parking lot trees, and those are still in use. I’ve seen some very good looking “pin oaks” in new parking lots, but I imagine that acorn drop can be a problem depending on location. A variety of other trees, including red maple cultivars, are being used as an alternative.

Acer rubrum 'October Glory'
Acer rubrum 'October Glory'

Two red maple cultivars seem to be getting the most use. The first one is Acer rubrum ‘October Glory’ which has a typical red maple leaf shape (3 lobes), a well-balanced oval shape, and a deep red fall color that leans a bit more towards crimson-red than orange-red. According to the patent record for this cultivar, it was selected not just for color but for long leaf retention in the fall. That trait was certainly evident this dry fall when leaves have persisted even past the third week of November, often all the way up to the top of the tree.

Based on an informal sampling of parking lots in my area, I would say that ‘October Glory’ is used most of the time (and for good reason if long lasting color is your goal). Occasionally, I find the second cultivar which is actually a hybrid of red maple and silver maple (Acer saccharinum) known as Acer x freemanii ‘Jeffersred’ but sold as Autumn Blaze®.  The Freeman hybrids were developed in 1933 at the U. S. National Arboretum by Oliver Freeman. Both parent species are native to Georgia and the Freeman hybrids have the attractive leaf shape, adaptability, and fast growth rate of the silver maple plus the good fall color and strong wood of the red maple. The shape of this maple is a bit more pyramidal than oval and the color is a strong red-orange. The leaves definitely drop earlier than the other cultivar.

Acer x freemanii
Considerations when using these red maples in the landscape: shallow roots mean they need a good island around them, and plant them in full sun for best color. ‘October Glory’ maples turn a more orange-red when they don’t have sufficient sun.

Parking oaks and maples are a good mix for color
Parking lot trees must be able to handle tough conditions, especially given the small spaces that trees are often forced to occupy. Between the oaks and the maples, our Georgia natives are well represented; I see also river birch (Betula) and holly hybrids (such as Ilex x attenuata). Unfortunately, non-native trees are being spec’ed into the professional landscapes too – non-native elms, pistache, and gingkos are being used more often these days, perhaps even as a reaction to the overuse of oaks and maples.

Expanding tree islands would help provide better conditions for more tree selections – fewer trees but more plant diversity would be the result. Nurserymen could experiment with more natives like hawthorns (Crataegus), American elms (Ulmus), and blackgum (Nyssa). As more and more land is developed into human spaces, using our native trees to landscape them is a small giveback that we can do to help support the insects and critters that live here with us.

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