Summer of trees at the Arboretum: Red Oak

Red oak (Quercus rubra), or northern red oak, is a fast-growing shade tree that is native from Nova Scotia to Iowa and Minnesota. Younger trees begin with a rounded form, but the top of the canopy plateaus with age.

With a negligible tap root, it transplants easily, adapting to shallow soils with good drainage. Red oaks have become popular as street trees, as they can also tolerate air pollution. Performing best in slightly acidic sites, the leaves suffer from iron chlorosis when planted in high pH soils.

Red oak properties

• Deciduous; brown leaves may persist through winter, then pushed off by new spring growth
• Height: typically 60 to 75 feet, 100 feet in the wild
• Width: 60 to 75 feet
• Habit: round, with the top flattening with age
• Acorns: alone or in pairs, ¾ to 1 inch long
• Bark: on old trees, deeply furrowed with wide, flat ridges
• Leaves: pointed tips, compared to white oaks; excellent color changes throughout the growing season

Best growing conditions

In landscapes, the red oak is a remarkable shade tree if given room to grow. Reaching up to 75 feet high and wide, its symmetrical form is admired from any angle. Requiring full sun, foliage color is excellent throughout the growing season. Leaves emerge with pink and red shades, become dark green during the summer, and turn brick red or bright red in the fall. Foliage turns brown and hangs on through winter.

• Hardiness zone: 3 to 7
• Full sun
• Recommended soil properties:
  • Soil pH: 6.5 is best, iron chlorosis in soils at or above 7.5
  • Best in moist, sandy loam soils
  • Needs well-drained soil, some drought tolerance
  • Some tolerance to air pollution and salt
  • Before planting, have your soil tested by the U of M Soil Testing Lab.

Useful to so many

Acorns from the red oak are favored by birds and squirrels. Edwards’ Hairstreak butterflies use young red oaks for egg overwintering and larval feeding. Banded Hairstreaks also use them for the caterpillar life stage.

An important food source for indigenous people, acorns were boiled and processed to remove tannins before consumption. The bark of the red oak was also used for astringent, to reduce fever, and to relieve pain. During the Civil War, red oak was used for medicinal purposes as conventional medicines became scarce.

Oaks in the southern and western parts of the United States are declining due to pest issues, climate change, fire and fire suppression, economical development, and agricultural use of land. However, conservationists believe red oaks will continue to thrive due to their adaptability and dominance in their native communities.

Common problems

Though they are robust trees, red oaks share many problems with their white oak relatives. Both are susceptible to cankers, leaf spots, wood decay, and rusts. Two-lined chestnut borers typically attack stressed trees. Reduce stress by providing adequate water in times of drought.

In Minnesota, the main concern is oak wilt, a fungal disease spread by insects or root grafts between trees close to each other. Death can occur the same year they are infected, with symptoms beginning as branch death at the top of the tree. Visit Oak wilt in Minnesota for more information.

For other common oak problems in Minnesota, visit What’s wrong with my plant? - Oaks.

Buying red oak

Red oak (Quercus rubra) is listed in the Plant Information Online database, which offers plant and seed sources throughout North America. We recommend buying from local nurseries, as Minnesota-grown plants are already adapted to our climate and soils, require less transportation and fuel costs, and are unlikely to introduce or spread invasive species from other parts of the country.

Our favorite red oak at the Arb

This beauty sits at the edge of our Annual Garden, so it gets a lot of attention from our visitors. It used to have iron chlorosis because of the limestone under its roots. The Arb hired a local tree care company to inject iron into the base of the tree, and the leaves emerged a deep green the next year. We will repeat the iron treatments as needed to ensure this tree’s health in less-than-optimum soil conditions.

Red oak is on our Interactive Tree Trek map. To find one, click the layers icon in the top right, and add Tree Trek. The map will show you where to go, and give you a little info to take with you!