Highly tolerant of drought, Bur Oak are slow growing oak that has a deep taproot and an extensive lateral root system. These may live past 300 years old and grow taller than 150 feet tall.
Quercus macrocarpa (Bur Oak, Mossycap Oak, Blue Oak, Scrub Oak)
Hardiness Zones: 3-8
Height: rarely to 52 meters (170 feet) tall
Diameter: spreads to 24 meters (80 feet), trunk d.b.h. to 120 centimeters (48 inches) around 100 years old
Growth Rate: slow above ground (around 30 centimeters (12 inches) annually), rapid root growth
Age: Fruit production begins at age 35, peaks around 75-150; trees lives from 200-400 years old.
Root System: enormous taproot and extensive lateral roots
Subspecies: hybridizes with Q. alba (White Oak), Q. gambellii (Gambel Oak), Q. bicolor (Swamp White Oak), Q. lyrata (Overcup Oak), Q. michauxii (Swamp Chestnut Oak), Q. muehlenbergii (Chinpakin Oak), Q. robur (English Oak), Q. stellata (Post Oak), Q. virginiana (Live Oak)
Tolerates: drought, shade (moderate), fire (moderate)
Problems (major): Oak kermes, oak leaf blister, oak skeletonizer, oak lace bugs, redhumped oakworm, chestnut blight, root rot (shoestring, cotton), anthracnose, dieback, cankers, powdery mildew, scale, leaf miner, June beetle, galls, borers, caterpillars, nut weevils, long-term flooding.
Problems (minor): Oak wilt, flooding (short-term)
Poisonous: none known
Soil requirements: prefers dry to moist, well-drained soils
Air requirements: more tolerant than other oaks
Watering requirement: somewhat low to moderate
Sun requirement: full sun required, minimal shade tolerance
Leaves: to 30 centimeters (12 inches) long, alternate, 5-9 lobes, dark green, yellowish-brown in autumn
Flowering structure: inconspicuous male yellow-green catkins to 10 centimeters (4 inches) long, female catkins green with bits of red in single spikes
Flowering frequency: April, emerge after leaves grow
Fruits: acorns to 4 centimeters (1.5 inches) in diameter, warty cap with long margins, mature in one season
Bark: brown/grey, scaly, becomes ridged with age
Form: rounded when young, becomes broad and wide with age
Seeds require stratification: yes
Monoecious or Dioecious: monoecious
Found in limestone bluffs and bottom-lands, these occasionally invade grass praries because of their extraordinary root system.
These are occasionally planted as large shade trees in dry areas.
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