Those of us with long driveways often fantasize about having a stately planting of matching driveway trees on both sides, forming a shady “tunnel”. This type of planting is called a colonnade. We’ve all seen them; perfect matching ranks of mature trees marching along the lane leading to the house of our dreams. My favorites are down in Bourbon County, Kentucky, mature pin oaks planted more than a hundred years ago.
Choosing and planting heirloom trees like this takes some planning. Not only must the trees match, but they should be planted at the same time in exactly the same way, and carefully trained so that they continue to match as they mature. For many years, our tree of choice for lining driveways has been a variety of ornamental pear called “Cleveland Select”. It is easy to limb up to a high crown when young, forms an attractive high oval or cone-shaped crown, and has an alternating branch structure so it won’t split under ice load like Bradford pear. Cleveland Pears are fast growing, very adaptable to poor soils, drought tolerant and disease resistant. They hold their leaves longer than most trees, have showy red fall color and white blooms in spring. We have thirty-three matching Cleveland pear trees along the highway frontage of our own farm.
Unfortunately, the state of Ohio has classified all ornamental pears, including Cleveland Select, as invasive plants. Nurseries have stopped planting them, and they can only sell their existing stocks for a few more years. As of January 1, 2023, Callery pear will be illegal to sell, grow, or plant in Ohio. You can find details on the Ohio Department of Agriculture regulation restricting invasive plant species, at https://agri.ohio.gov/divisions/plant-health/invasive-pests/invasive-plants.
Tree colonnades are, and will always be, a desirable macro-landscape feature. Now that easy, fast-growing Callery pears are no longer available, we need to find alternative tree varieties to achieve the colonnade effect. Our current favorite is the northern red oak, Quercus rubra, and we’ve planted several red oak colonnades in recent years with good success. Red oak has upward-arching limbs, an important trait because vehicle clearance is key to low-maintenance driveway tree plantings.
Pedigree really matters if you want the trees to match over time. Start out with quality, matching trees so that they will be from the same seed stock. “Limb up” the lower branches so that the bottom limbs on all the trees are at the same height. Driveway trees should be spaced so that when they are fully mature they won’t crowd each other. Spacing should be about 1-1/2 times the mature tree spread; further apart will look skimpy. If you want the trees to form an archway over the drive, they should be the same distance across from each other as their mature spread.
Whichever tree you choose for your colonnade, pay attention to growing conditions along your driveway. Soil fertility and drainage can vary from one side to the other, or along the drive, which will cause trees to grow unevenly over time. If there are obvious, extreme differences in moisture or soil quality along your driveway, we wouldn’t suggest attempting a colonnade of matching trees.
Trees that overhang driveways and streets must be “limbed up” high enough to provide clearance for vehicles. This should be done in stages over several years, particularly if you start with fairly young trees. Spreading trees like Pin Oak and Norway Maple should be avoided because they will eventually block traffic. Upright growers like Gingko, Red oak, Elm, Zelkova or pyramidal hornbeam are better choices since their limbs naturally arch upwards. There are many tree cultivars bred specifically for narrow spaces like city sidewalks. Shade trees like Shademaster honeylocust or sugar maple work well too, but should be spaced further apart and further from the roadway
After years of diligent training we have an impressive line of perfectly matched trees along our frontage, but we’re sorry now that we chose ornamental pears instead of longer-lived, sturdier hardwood trees. Ornamental pears are short-lived, softwood fruit trees. If we had it to do over, we would be more patient. Then our stately colonnade would give our great-great grandchildren something to remember us by.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.