Bur Oak (Quercus macrocarpa) is a massive tree from the white oak family. Its acorns are the largest known oak fruits in Colorado and the rest of North America.
While there’s still some debate about whether the bur oak is truly native to Colorado, it has undeniably become a favorite along Denver’s streets. Its strong structure and striking appearance make it a top choice for planting in the city.
Appearance
Mature bur oaks have sturdy trunks and wide canopies. When fully grown, their massive crowns look like a giant green umbrella. This oak’s leaves are big and bold. They grow to be about 6-12 inches long and 3-5 inches wide. The leaves are deeply lobed with rounded edges. They are dark green in the summer and golden brown in the fall.
Young bur oaks have a smooth bark. However, when they get older, it becomes rough and deeply rigid.
Mature bur oaks can reach 60-70 feet in height. However, some giants can grow over 100 feet tall. Their canopies often spread just as wide as they are tall, which means a bur oak can easily cover a 70-foot wide area with shade. Because of their size, bur oaks need a lot of space to grow.
Why Bur Oak Grows Well in Denver
Bur oak has found a comfortable home in Denver because, once established, it is extremely tolerant of drought. Denver’s semi-arid climate doesn’t faze it. The tree’s deep root system allows it to tap into water far below the surface, helping it survive dry summers. Bur oak is also resistant to many pests and diseases.
There is still some debate among botanists about whether the bur oak is native to Colorado. Naturally, its range covers the Midwest and parts of the eastern Great Plains. While it may not have originally grown in large numbers in Colorado, it has been widely planted here for over a century.
Bur oaks can survive in different types of soil. They can grow in clay, loam, sandy soils, and even soils with low fertility. However, these trees perform well in deep and moist soils with a slightly alkaline to neutral pH.
Elevation and Temperatures
Bur oak does better at lower to mid-elevations, so it doesn’t fare well in the high Rocky Mountains. Usually, this tree grows well up to about 5,300 feet in elevation. This covers Denver and some nearby areas. When it comes to higher elevations, the shorter growing seasons become too harsh for bur oak to thrive.
This oak tree is cold-hardy. It can survive winter temperatures as low as -20°F. Coupled with impressive heat tolerance, this ability makes the bur tree perfect for Denver’s weather extremes.
Bur oak loves full sun. It needs at least six hours of direct sunlight every day to grow strong and healthy. That’s why these trees do best in wide-open spaces where the sunlight hits them from all sides.
Interesting Facts
Here are some interesting facts about this beautiful giant:
- Fire-resistant bark: Thanks to its thick, corky bark, bur oak can survive grass fires that would kill many other trees.
- Very long-lived: A healthy bur oak can live for 200 to 400 years. Some exceptional trees have lived even longer.
- Wildlife magnet: Its acorns are a major food source for squirrels, deer, wild turkeys, and other animals.
- Pioneer species: Bur oaks are often among the first trees to grow back after prairies or woodlands are disturbed.
If you’d like to learn more about bur oaks or other trees in Denver, please get in touch with our experienced arborists today.