Willow Oak (Quercus phellos)

Oaks, Willow Oak

Quercus phellos, commonly known as the willow oak, is a deciduous tree native to the eastern and central United States. It is particularly prevalent in the Atlantic Coastal Plain and the lower Mississippi River Valley. The willow oak is valued for its attractive form, dense canopy, and adaptability to urban environments, making it a popular choice for street trees and landscapes. Its narrow, willow-like leaves distinguish it from other oaks, and it is known for its rapid growth and longevity.

I. Appearance and Characteristics 

Quercus phellos, the willow oak, is a North American species of a deciduous tree in the red oak group of oaks. It is native to the south-central and eastern United States.

It is most commonly found growing on lowland floodplains, often along streams, but rarely also in uplands with poor drainage, up to 400 m (1,300 ft) in altitude.

It is a medium-sized tree growing to 20–30 meters (65–100 feet) tall (exceptionally to 39 m, 128 ft), with a trunk up to 1–1.5 m (3+1⁄2–5 ft) in diameter (exceptionally 2 m or 6+1⁄2 ft). It is distinguished from most other oaks by its leaves, which are shaped like willow leaves, 5–12 centimeters (2–4+3⁄4 inches) long and 1–2.5 cm (3⁄8–1 in) broad with an entire (untoothed and unlobed) margin; they are bright green above, paler beneath, usually hairless but sometimes downy beneath. The fruit is an acorn, 8–12 millimeters (5⁄16–15⁄32 in) long, and almost as wide as long, with a shallow cup; it is one of the most prolific producers of acorns. The tree starts acorn production around 15 years of age, earlier than many oak species.

Willow oaks can grow moderately fast (height growth up to 60 cm or 2 ft a year), and tend to be conic to oblong when young, rounding out and gaining girth at maturity (i.e. more than 50 years).

As an oak tree, willow oak can be mildly toxic if ingested. It causes mild to moderate symptoms, especially if eaten in large quantities. This toxicity is attributed to the tannins contained in the young leaves and acorns. These plant parts, if eaten, can cause stomach upset, constipation, diarrhea, bloody stool, and extreme thirst. In extreme cases, the kidneys can also be affected. These trees are popular ornamentals in parks and yards, meaning they’re easily accessed by children who might accidentally pick up and eat the leaves or acorns.

II. How to Grow and Care

Sunlight

Willow oak should be planted in a field with full sun. It gives shade, shady plants can be planted under it.

Temperature

Willow oak grows in a large range of temperatures. It is adaptable in hardiness zones 5-9.It prefers well drained soil with adequate ventilation in the tree canopy. Willow oak will not do well in standing water. Also, leaf molds pose serious threats if the leaves cannot dry out in the wind. So make sure they are not stuck against buildings where rainwater may drain.

Watering

Keep soil moist but well drained. Oaks form a taproot and will draw moisture up from below. So make sure there is humid soil if you dig down a few inches, but do not flood the topsoil. Reducing summer water apply will make willow oak more healthy, they tolerate summer dry spells very well.

Soil

Ideal soils are well-drained loam, sandy-loam, or sandy-clay soils. Some alluvial fan areas and silts harbor good oaks stands. The key in all of these is that the soil is well-drained. Standing water cannot be tolerated by oaks.

Fertilizing

Willow oak can survive and thrive without supplemental fertilization. But if you wish to give them extra nutrients you can add some of 12-6-6 (N-P-K) fertilizer. This has more of a ratio of nitrogen than phosphorus and potassium. Also, consider the natural environment of oaks. They grow where there is lots of forest litter. This forest litter acts as natural mulch that breaks down into organic matter and humus. So one way to give some natural nutrition is to spread mulch by your oak trees. They will love the extra organic matter.

Planting Instructions

It may take a very long time if you want to get a mature oak tree from an acorn. But with patience, planting a small tree is still fun. Be sure to kill weevil larvae by soaking the acorns in 41 ℃ water for 30 minutes, stratify in moist sand in the refrigerator (not freezer), and plant in the springtime.

When planting a willow oak, choose a location with enough space to accommodate its mature size. Dig a hole twice as wide as the root ball and of the same depth. Place the tree in the hole, backfill with soil, and water thoroughly. Mulching around the base can help retain moisture and regulate soil temperature.

Pruning

Branches should be pruned to avoid moist pockets or where heavy branches may fall on people or buildings. Avoid having branches that grow with leaves tight together or pressed against buildings. If rain collects in these pockets then molds and fungi can attack. Willow oak love having their leaves dry out in a well ventilated breeze.

To ensure that no danger occurs from the brittle hardwood branches, make sure that heavy branches do not hang over walking paths or outbuildings. Also, do not let children play near oaks in a thunderstorm as they are susceptible to falling branches and lightning strikes.

Propagation

Propagation of willow oaks is typically done through seed (acorns). Collect acorns in the fall and plant them immediately or stratify them in moist sand or peat moss for sowing in the spring.

Transplanting

The willow oak thrives when transplanted in late winter to early spring (‘S1-S3’) as these conditions foster ideal root growth. Ensure your chosen location allows full sun to part shade exposure for optimal growth. When transplanting, be sure to handle this tree with care due to its sensitive roots.

Pests and Diseases

Willow oaks can be susceptible to pests such as the oak leaf caterpillar (Anisota senatoria) and the gypsy moth (Lymantria dispar). These insects feed on the leaves, potentially causing defoliation. Treatment includes the use of biological controls like Bacillus thuringiensis or chemical insecticides. The tree can also suffer from oak wilt, a fungal disease that can be managed by preventing wounds and promptly removing infected trees. Regular monitoring and proper care can help prevent and mitigate these issues.

III. Uses and Benefits 

Economic uses also are primarily as the wood for pulp and paper production, but also for lumber; it is often marketed as “red oak” wood.

The willow oak is one of the most popular trees for horticultural planting, due to its rapid growth, hardiness, balance between axial and radial dominance, ability to withstand both sun and shade, light green leaf color and full crown. Despite being heavily used in landscaping in the Southern US (in cities such as Washington, D.C., Raleigh, Charlotte, and Atlanta) around malls, along roads,… The trees tend to grow larger than planners expect, which often leads to cracked sidewalks. Azaleas, wood rose, and creeping mahonia will thrive underneath this tree.

Oak trees support over 800 caterpillar species in the United States. They are host plants for over 500 species of butterflies. Birds and mammals, including deer and squirrels, consume the acorns.

Willow Oak (Quercus phellos) Details

Common name Oaks, Willow Oak
Botanical name Quercus phellos
Plant type Native Plant
Hardiness zone 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Fast
Harvest time Fall
Height 40 ft. 0 in. - 75 ft. 0 in.
Width 40 ft. 0 in. - 75 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Gold/Yellow
Leaf color Green