Quercus macrocarpa, commonly known as the Bur Oak or Mossycup Oak, is a member of the Quercus genus within the Fagaceae family. It belongs to the white oak group, recognized by its leaves with rounded lobes and acorns that mature in one season. The species name “macrocarpa” refers to the large size of its acorns, which are indeed among the largest of any oak species.
The Bur Oak is indigenous to North America, with a broad native range that extends from the southern regions of Ontario, Canada, south through the eastern Great Plains into Texas, and eastward to Pennsylvania. It’s known for its ability to thrive in a variety of habitats, from prairies and savannas to riverbanks and mixed hardwood forests, showing a particular resilience in both dry, well-drained uplands and moist, fertile lowlands.
Bur Oak has a deep historical connection with the landscapes it inhabits. Native American tribes utilized the Bur Oak for its durable wood, which was perfect for constructing canoes and tools, and for its acorns, which were a significant food source. European settlers also valued its timber for building, especially where other species were not as readily available in the prairies. The tree’s longevity, with some specimens living over 300 years, has allowed it to become a part of the historical fabric of North America, often marking significant natural or cultural landmarks. Its large, distinctive acorns are also culturally noted, giving the tree its common name “Mossycup” due to the hairy cap that partially encloses the acorn.
Quercus macrocarpa is well-suited to USDA Hardiness Zones 3 through 8. This wide adaptability means it can grow in a range of climates, from the harsh winters of the northern plains to the milder, yet still seasonally cold, conditions of the Midwest and South. It tolerates both drought and occasional flooding, making it versatile for landscaping and reforestation efforts across its native range and beyond. The tree’s preference for deep, loamy soils is well-known, but it also shows adaptability to various soil types, including clays and sands, provided there is adequate drainage. Its use in urban and rural settings has increased due to its resilience and aesthetic qualities, contributing to its popularity in parks, along streets, and in conservation projects.
Bur Oak (Quercus macrocarpa): Characteristics
Growth Habit
Quercus macrocarpa has a distinctive growth habit, often developing a broad, spreading crown with large, heavy branches that can sweep to the ground in open areas. In contrast, when grown in dense forests, it tends to have a more upright, narrower form. The tree’s silhouette is rugged and majestic, with a sturdiness that reflects its ability to endure harsh conditions.
Size
Bur Oaks can grow to substantial sizes, reaching heights of 70 to 80 feet, with some trees exceeding 100 feet. Their spread can be equally impressive, especially in open landscapes, where the crown can extend to or beyond the tree’s height, offering significant shade coverage.
Growth Rate
The growth rate of Bur Oak is considered moderate to slow. Young trees might grow about 1 to 2 feet per year, though this slows as the tree matures. Its growth can be particularly slow in its first few years, emphasizing the need for patience in cultivation.
Leaves
The leaves of Quercus macrocarpa are simple, alternate, and notably variable in shape, often obovate to nearly round with 5 to 9 rounded lobes. They can be 6 to 12 inches long, with a dark green, lustrous upper surface and a paler, sometimes slightly hairy underside. In autumn, the leaves turn yellow or brown rather than bright colors, often remaining on the tree well into winter.
Lifespan
Bur Oaks are among the longest-lived oaks, with some individuals reaching over 400 years. Their longevity, combined with their resilience in extreme weather conditions, makes them enduring features of landscapes.
Bark
Young Bur Oaks have smooth, gray bark that becomes deeply furrowed with age, creating a rough, dark, and scaly texture. The bark’s appearance adds to the tree’s rugged aesthetic and provides habitat for numerous species.
Roots
The root system is robust, with a deep taproot in youth for anchorage, transitioning to a wide-spreading network of lateral roots as it matures. These roots are strong and extensive, which can pose challenges in urban settings due to their potential to disrupt sidewalks or foundations but also contribute to the tree’s stability and drought resistance.
Additional Characteristics:
- Acorns: Bur Oak produces some of the largest acorns among oaks, often 1 to 2 inches long, with a distinctive mossy cap that covers much of the nut. These acorns are an important food source for wildlife.
- Wood: The wood is hard, heavy, and durable, making it valuable for furniture, flooring, and construction where strength is needed. However, it’s not as commonly used for barrels due to its high tannin content.
- Tolerance: This species exhibits remarkable adaptability, tolerating both drought and occasional flooding, which makes it suitable for a wide range of environmental conditions.
- Ecological Value: Bur Oaks are keystone species in their ecosystems, supporting a vast array of life from insects to large mammals, contributing to biodiversity and soil conservation.
Cultivation
Site Selection
When choosing a site for Bur Oak, consider its mature size and growth habit. It prefers full sun for optimal growth but can tolerate some shade, especially when young. The tree is adaptable to a variety of soil types but thrives best in deep, well-drained loamy soils, though it can grow in clays or sands if the drainage is adequate. Given its tolerance to both drought and flooding, it’s suitable for sites that might experience variable moisture conditions.
Planting
- Timing: Plant during the dormant season, from late fall to early spring, to reduce stress on the tree.
- Planting Hole: Dig a hole twice as wide as the root ball but no deeper, ensuring the root flare is level with or slightly above ground level to prevent water accumulation around the trunk.
- Process: If from a container, gently remove the tree, tease out any circling roots, and place in the hole. For balled and burlapped trees, remove burlap from the top and sides, but keep the root ball intact. Backfill with native soil, firming gently to remove air pockets.
Watering
Water deeply after planting. Young Bur Oaks need regular watering to establish their root system, particularly during dry spells. Once established, they are drought-resistant but benefit from supplemental watering during extended dry periods. Reduce watering in the fall to help the tree prepare for dormancy.
Mulching
Apply a 2-3 inch layer of mulch around the base of the tree to conserve soil moisture, suppress weeds, and regulate soil temperature. Keep mulch away from direct contact with the trunk to prevent rot.
Fertilization
Bur Oaks typically don’t require regular fertilization if planted in good soil. If a soil test reveals deficiencies, a balanced, slow-release fertilizer can be applied in early spring, but avoid high-nitrogen fertilizers that encourage leafy growth over root development.
Pruning
- Formative Pruning: In the early years, prune to shape the tree, establishing one strong central leader if desired, and remove any competing or inward-growing branches.
- Maintenance Pruning: After establishment, limit pruning to removing dead, diseased, or crossing branches. Bur Oaks do not respond well to heavy pruning, so keep cuts minimal. Prune in late winter to early spring before new growth begins.
- Storm Damage: Only remove broken branches after storms; the tree will naturally shed unnecessary limbs over time.
Pest and Disease Management
Bur Oaks can be susceptible to oak wilt, especially in areas where this disease is common. Monitor for signs like leaf discoloration and wilting, managing through proper pruning practices and possibly fungicides. Other pests might include scale insects or galls, managed through integrated pest management focusing on natural controls when possible.
Long-term Care
- Support: Young trees might need staking in windy areas, but this should be temporary to allow trunk movement.
- Protection: Protect from deer and other browsers, especially in the early years, using tree guards or fencing.
- Urban Considerations: Plant with an awareness of its mature size; its expansive root system can impact nearby structures or utilities.