A.K.A. mossy-overcup oak, mossycup oak, white oak, blue oak and scrub oak.
- The second part of the scientific name or specific epithet, macrocarpa means large seed or fruit and the bur oak produces the largest acorns (up to 2 inches in diameter) of all the oaks found in North America.
- Fully mature trees can grow massive 8 – 10′ diameter trunks with a huge open crown, that can be as wide as the tree is tall.
- Reaches heights of 70 – 100′ and occasionally more.
- They are slow growing trees, although, when they are young they can grow more than 12 inches a year in height and grow long tap roots very quickly.
- Lifespan is approximately 400 years.
- Simple leaves are broad and 6 – 10 inches in length with lobed margin.
- Bur oak is monoecious.
- Flowers – Catkins are 4 – 6 inches in length.
- Fruit – produces acorns every 2-3 years.
- It is drought and fire resistant.
- Bur oaks fair well in urban environments.
- Some damaging insects include oak webworm, oak skeletonizer, oakleaf caterpillar, oak lacebug, redhumped oakworm and June beetles.
- Common problems include: susceptible to (fungi) Strumella canker, cotton root rot and Oak wilt – sometimes through rare root graphs with red oaks.
- Plant Hardiness Zones 3 – 8
Photographs of the oldest bur oak in Boulder, Colorado.