bur oak

Photo: Heath Cajandig — CC BY 2.0 · source

Survives zone 3 through 8

Harvest calendar

Best planted in early spring after your last frost, or in fall before the ground freezes, depending on your climate.

Acorns edible only after leaching out bitter tannins in water, then ground into flour or roasted. Bur oak is in the low-tannin white-oak group and among the easiest, sweetest acorns.

Hardiness

Zone 3–8

Habit

Tree

Edible part

Nut

Ripens

Sept–Oct

Mature size

Large tree 20–30 m with a massive spreading crown — not containerable

Light

Full sun — acorn masting needs a sunlit crown

Soil pH

Castanea 4.5–6.5 — ⚠ LIME-INTOLERANT (calcifuge, unlike other nut trees). Quercus/Fagus 5.0–6.5

Environment

Temperate

Native range

Central North America — Saskatchewan east to New Brunswick, south-west to Texas and north to Montana; prairie edge, savanna and bottomland, and the most drought- and fire-tolerant of the group.

Status

Wild

Years to fruit

3–5 yrs grafted

Growth speed

30–60 cm/year — medium, slower in youth while the taproot is built.

Spacing

1400 cm (551 in) apart — about 196 m² (2110 sq ft) per plant

Leaf shape

Alternate and very large, up to 23 cm, with rounded lobes separated by sinuses cutting almost to the midrib — often nearly dividing the leaf in two — dark green above, pale and downy beneath.

Root system

A strong taproot dominates the first three years, driving 60–120 cm down while the top makes only modest growth — which is why oaks resent being moved once established and why nursery stock should be planted young. Mature trees add a wide lateral network.

Fruit description

The largest acorns of any native North American oak, up to 4 cm across, set in a deep cup fringed with a conspicuous mossy burr around the rim that encloses a quarter to over half the nut; sweet and among the best for eating.

Propagation

⚠ White-oak-group acorns germinate in autumn, the moment they drop — they must be sown fresh and cannot be dried or stored like red oak acorns. Sow immediately in deep pots or straight into position, protected from mice; little or no cold stratification is needed.

Pollination

Wind-pollinated, monoecious; masting (heavy crops every 2–4 years) — several trees improve pollination

The edible parts listed above are a starting point, not a field guide. Identify a plant with certainty — ideally against a local authority — before eating any part of it, and read the full disclaimer. Spotted something wrong? Report it.