Quercus macrocarpa Seeds | Bur Oak
LATIN NAME: Quercus macrocarpa
COMMON NAME: Bur Oak
Plant Profile
Quercus macrocarpa carries the largest acorn of any North American oak, and the cup that holds it is fringed with a mossy scale that gives the tree its other name. The acorn can be four centimetres across and is often half the length of the nut. The leaves are large, deeply lobed and widest above the middle, with a distinctive notch that cuts almost to the midrib.
The species grows from the Atlantic states to the Great Plains, on prairie edges, in river bottoms and on dry uplands, and it is the oak of the transition zone between forest and grassland. Old trees are broad and open, with a thick, deeply furrowed bark that resists fire, and they can live for three hundred years.
Science & Biotechnology
Bur oak is the most drought- and fire-tolerant of the eastern oaks, and it manages both with the same strategy: a deep taproot that reaches water and a thick bark that insulates the cambium. A seedling spends its first years building the root rather than the shoot, which is why the tree is hard to transplant and why it survives on sites where other oaks fail.
The acorn crop varies wildly between years, a habit called masting. In a heavy year the trees produce far more acorns than the animals can eat, which guarantees that some survive; in a light year almost none do. The mechanism is not fully understood, but it involves weather, stored reserves and pollination, and it is why a good acorn year is followed by two or three poor ones.
Uses & Benefits
The wood is hard, heavy and strong, and it is used for flooring, for barrels, for railway sleepers and for furniture, though the tree is slow and the timber is not as prized as white oak. The acorns are edible after leaching the tannins, and they were a food for several peoples of the plains, ground into flour.
The tree is planted as a shade tree and in shelterbelts on the prairies, where it is one of the few large trees that will grow. It is also used in restoration plantings on dry sites, and in parks for the shape of the crown and the size of the acorn.
Growing from Seed
Acorns should be sown in autumn, in deep pots, since the radicle emerges within weeks and the taproot grows fast. Do not let them dry out. Germination is in spring, and the seedling should be grown in a deep container for two years before planting out, because the taproot is easily broken.
The tree wants full sun and a deep, well-drained soil, and it tolerates drought, clay and prairie wind. It is hardy to about minus thirty-five. Plant it small, protect it from deer and from mowers, and expect it to spend its first years underground; a bur oak grows slowly above the surface and quickly below it.
Our Take
A long-term tree for dry ground and big acorns, and one that rewards patience rather than watering. Plant it small and then leave it alone.
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