Hills Oak is often found on dry, acidic soils with low nutrient content. The glossy green leaves have deep sinuses, and the tree tends to hang on to lower branches. A good choice for reliable fall color in tough, droughty sites, but will struggle in heavy clay soils. May also be known as Scrub Oak or Northern Hills Oak.
Wisconsin Native: Yes
USDA Hardiness Zone: to zone 4
Mature Height: 60 feet
Mature Spread: 45 feet
Growth Rate: Slow
Growth Form: Tree, oval
Light Requirements: Full Sun
Site Requirements: Tolerates drought, requires well drained soil
Flower: Monoecious, insignificant male and female flowers emerge in spring with leaves
Bloom Period: April-June; variable
Foliage: Glossy Dark Green
Fall Color: Red
Urban Approved: No
Fruit Notes: Acorn, small with black stripes
Waukesha, Milwaukee, Racine and Portage Counties, WI
Hills Oak should be sited only where soils are sandy and well drained. It is an excellent choice where fall color is desired but moisture is limited. This oak is a good alternative to Sugar Maple or Red Oak when soils are excessively well drained.
Although its acorns aren’t as sweet as those in the White Oak Group, Hills Oak does provide value to wildlife for mast and habitat. Gray squirrel, deer, blue jays, wood ducks, and king birds all benefit from this tree as a food source.
The endangered Kirkland’s Warbler likes to nest in the trunk cavities.
All oaks are susceptible to Two-Lined Chestnut Borer during the establishment period after planting. Apply a systemic insecticide containing imidacloprid when planting to protect the tree from this insect.
Do not prune Hills Oak during the growing season. Doing so will allow infection by Oak Wilt, which is always fatal. Prune only during the dormant season when there are no insects present.
The thin bark make it susceptible to deer and mechanical damage. Maintain a mulch ring around the base of the tree to avoid accidentally wounding the bark when mowing. Apply a trunk wrap in fall to protect the trunk during the dormant season.
We invite you to check out the Arborist For Hire lookup at the Wisconsin Arborist Association website to find an ISA Certified Arborist near you.
Hills Oak is the most susceptible to Oak Wilt of all our native oaks. As such, it is imperative you do not prune or damage the tree during the growing season and only prune during winter. Oak Wilt is always fatal, and has been observed to kill Hills Oak in one season after infection.
Quercus ellipsoidalis is an early successional species and does not compartmentalize well. This means it is more prone to decay and structural damage than the sturdier Red Oak or Bur Oak. However, it still provides value as a faster growing forest margin species and its tolerance of dry, barren sites is useful where other trees may not succeed.
Maintaining tree vigor is the best practice for avoiding insect and disease damage. When stressed, Hills Oak is susceptible to a variety of fungal and insect pathogens. During periods of drought take care to provide enough moisture and use a mulch ring to protect the roots.
When grown naturally, Oaks develop a coarse, deep root system with a taproot. This has made them historically difficult to transplant as balled-and-burlapped (B&B) trees because much of the root system is lost in the harvesting process. Our trees are unique because they are root pruned from the start to develop more fibrous fine roots. When harvested, our B&B oaks contain more fibrous roots, making them tougher and easier to transplant than oaks not given our unique treatment process.
Hills Oak is adapted to fire, like Bur Oak, but does not possess the same corky bark. Instead, the tree survives a disturbance by resprouting from its trunk. Its deep, extensive root system allows it to thrive in exceedingly dry conditions and is a component of Pine Barrens. In Wisconsin, Hills Oak can be seen on forest margins in the central sands country. Wherever found, it’s a good sign that the soil beneath is low in fertility and moisture.
Hills Oak should be paired with other species that tolerate dry, acidic soils. Consider using American Filbert, White Pine, Goldenrod, or Wild Lupine.