Quercus phellos - Willow Oak

If you have space for just one shade tree, consider an oak! Botanists, foresters, and ecologists tend to rate oaks among the most ecologically important trees in North America - with around 90 species found across 85 percent of the nation's counties. They provide more food and shelter for wildlife than any other group of trees, making them "keystone species." Here in the “Keystone State”, where forests and woodlands are the default, nowhere is this more demonstrably true.

The environmental benefits of oaks don't stop there. Due to their size, habit, and longevity, they’re remarkably effective in managing erosion, buffering the worst effects of wind and storm runoff, and storing carbon. Of course, oaks are fantastic trees for use in gardening and landscaping which is our primary focus here.

Picturesque and attractive in habit and form, oaks make great focal points and specimens. They naturally and effectively anchor our manmade landscapes to the land. When sited properly, they buffer our homes and buildings from harsh winter winds and shade them from brutal summer heat. Most oaks are adaptable and extraordinarily resilient. Some are tolerant of extremes. Here at the nursery, it's rare for them to need warranty replacements.

In Pennsylvania and the Mid-Atlantic region, there are 20 or so native oak species. In nurseries, including ours, you’ll usually find even more, as well as various hybrids and cultivars. Because of this, there's an oak for almost any outdoor space.

Willow oak (Quercus phellos) is a particularly great oak because of its first-rate adaptive nature, attractive habit, and unique small leaves. The leaves, which are narrow and lanced-shaped like a willow's, typically make for easier cleanup. While we try to remind folks that leaves aren't litter, it's undeniable that the leaves of this oak don't take up the same space on lawns and walkways that leaves from other oaks (and most trees!) do.

Willow oak is indigenous to most states and counties throughout the Southeast, with Pennsylvania occupying the northern limit of its native range.  Similar to White oak, within its range, it can be found growing in a variety of habitat ranging from moist lowlands to drier uplands and everywhere in between.  This translates to great versatility when planted in our gardens and landscapes. It will even tolerate moderate flooding and brief droughts (once established). It also transplants easily, seldom going through prolonged periods of “transplant shock ". This tree is often used as a street tree in some areas, with Washington DC hosting many great specimens along its streets and urban centers.

While not garish or gaudy, Willow oak is undeniably a handsome tree. In youth, bark is a smooth, light gray and becomes more darker and more furrowed with age. Fall color rangers with tones in between an attractive yellow and a respectable russet. Oaks are usually one of the last groups of trees to change colors in fall, usually 2-3 weeks after maples do, prolonging autumn color.

Most oaks practice "marcescence" which means young trees don't drop their leaves till new leaves emerge in spring. On older trees, leaves on the bottom of the crown hold till spring while leaves higher up drop in fall. One theory that explains this phenomenon is it helps protect buds from herbivory. Regardless, this phenomenon adds winter interest to the tree by way of texture, color, and the sound of rustling leaves.

Oaks don't produce copious amounts of acorns annually. Instead, they choose to produce large quantities once every 2-5 years (provided they are pollinated by other oaks). Years of heavier acorn production are called "mast years." Oaks usually don't produce significant acorns until they're a couple decades old. While some see acorn production as a nuisance, we encourage you to think of it as providing a valuable resource to the animals and ecology of your yard and neighborhood. It's certainly wise, however, to carefully select a good site for any oak or other large tree. Maybe the middle of the lawn is a wiser spot than above the swimming pool, for example.

For the layman, oaks are generally organized into three categories: red oaks, white oaks, and live oaks. This helps with identification as well as care. Live oaks are typically evergreen that are found further south. All native oaks to Pennsylvania are in the red oak and white oak groups. Willow oak is in the red oak group. Leaves are typically identified by having pointed lobes although Willow oak is a bit of an anomaly in this regard. They drop their acorns in fall and germinate in spring, providing a food source for birds and mammals throughout the winter.

The reason oaks are so well utilized is that while oak tannins are bitter, they aren't highly toxic or lethal. This is evidenced by the 500+ species of caterpillars of butterflies and moths that are supported by oaks. (Remember, if we want pollinators and healthy bird populations, we need caterpillars!). And of course, the acorns are rich in nutrients for mammals and birds. Acorns can be soaked and ground into flour to use in baking as well. Acorns of oaks in the red oak group typically have more tannins than white oak acorns which requires a lengthier soak to remove them.

The wood and branching structure of Willow oak is very strong. Unlike rapid growing trees with brittle wood, such as willow and poplar, this isn't a tree that's prone to rotting, splitting, and falling on homes during windstorms. There is usually a trade off with wood strength and growth rate. Willow oak strikes a good balance with its moderate rate of growth while not being inherently prone to structural deficiencies. That said, we advise planting large trees the radius of a mature crown away from structures. As this species typically matures at 50-60' wide in most landscapes (at least this far north), we suggest planting this tree no less than 25-30 feet from your house. While most native oaks in our region can live for centuries, Willow oaks have shorter lifespans: usually around 100 years. Nevertheless, with the right conditions and care, it's possible your Willow oak can still be around for generations.

Despite being inherently hardy, some oaks in the eastern US have fallen prey to two introduced pathogens in recent decades: oak wilt and bacterial leaf scorch. To reduce the risk of introducing these pathogens into your tree, only prune (if you must at all) during the colder months (November through March). Pruning during the warmer months leaves open wounds that run the chance of attracting insects that might transmit these pathogens into the tree’s vascular system. Oaks in the red oak group are more prone to these pathogens than white oaks so it's imperative to bear this in mind.

Next time you decide to take hike Boyce Park, if you enter from the Boyce Park office off Old Frankstown Rd, you can find a large (but not fully grown) Willow oak planted in a grassy area between the parking lot and the road. You'll also find persimmons and a few other less-common trees.

If deer are a problem for you, we recommend you provide your tree with protection, such as a metal cage, until the tree is large enough to not be severely damaged. Once the tree is tall enough that the cage can be removed, protect the trunk with a trunk protector to prevent damage from buck rub from September through December. Tree guards are usually no longer necessary when the diameter of the trunk at chest height is 5".

Written by Plumline staff and not AI.