Carya glabra Seeds | Pignut Hickory
LATIN NAME: Carya glabra
COMMON NAME: Pignut Hickory
Plant Profile
The fruit is a pear-shaped nut inside a thin husk that splits completely into four valves when ripe, freeing a smooth light-brown shell with a pointed tip; the shell is thick-walled and the kernel small in proportion. The shagbark hickory by contrast holds its husk almost closed and yields a large sweet kernel, and the mockernut carries a thick husk reluctant to open at all. The three sort easily in autumn once the husks have opened, and the difference in the shell is the practical reason pignut hickory never became a commercial nut crop.
Leaves give the second clue. This species carries five, sometimes seven, leaflets smooth on both surfaces, with a leaf stalk that is also smooth, while shagbark and mockernut both have hairy stalks and fuzzy leaf undersides. Bark is equally diagnostic: young trunks are smooth and grey, older ones break into tight interlacing ridges rather than peeling into long strips. The buds are small and yellowish, unlike the large dark buds of shagbark hickory.
Because the kernel is valuable and the shell heavy, the nut is seldom carried far. Squirrels and chipmunks scatter-hoard nuts in shallow caches, and the proportion never recovered is how the species advances into new ground; nuts that are eaten disappear quietly, while buried ones sprout where they lie. The pointed tip is where the root emerges, and it drives downward well before the shoot appears.
The species grows on dry ridges and upland slopes, often on thin gravelly soils over sandstone or shale, and is a characteristic tree of the oak-hickory forest type covering large parts of the eastern United States. It tolerates drought better than shagbark hickory because of its deep taproot and can persist on sites too dry for beech and maple, though on richer, moister ground it is usually replaced by those species. Trees reach twenty-five metres on the better sites, with a narrow crown and a clean straight lower trunk.
Science & Biotechnology
The walnut family is known for naphthoquinones, of which juglone is the best studied, and hickories produce related compounds in their husks and leaves at concentrations far below those of the walnuts; the husks also carry astringent tannins. Hickory litter is therefore less allelopathic than walnut litter, which is why tomatoes and other sensitive plants grow closer to a hickory than to a black walnut. In the kernel, the chemistry is dominated by oil, and the kernels were once pounded into a milky food that early colonial writers recorded under the Algonquian name pawcohiccora.
Hickories are difficult to propagate vegetatively: the wood is dense, a graft calluses slowly, and seedlings have a long taproot that makes lift-and-heel operations risky. Almost all of the genus’s propagation research has been done on pecan, where somatic embryogenesis from immature seed tissue and shoot culture of mature material are established, and where rootstock breeding has a commercial purpose. For pignut hickory, seed remains the practical route.
Uses & Benefits
Hickory wood is heavy, close-grained and unusually resistant to shock, which is why it has been the standard material for axe handles, hammer shafts, pick handles, rake teeth and ladder rungs, and why it went into wheel spokes, wagon parts and early golf club shafts. Its heat value is high and it splits cleanly for fuel. The same dense dry-burning character made it the traditional smoking wood of the American South, where the flavour it gives cured pork became a regional signature.
Growing from Seed
Sow the nuts as soon as they are collected, because drying destroys them. Use a bed or deep container of two parts loam, one part leafmould and one part sharp sand, and set each nut on its side about three centimetres deep with the pointed end slightly downward so the root can leave cleanly. Protect the bed with wire mesh laid flat and pegged down, since mice and squirrels will clear a sowing in a single night. Leave it outside through the winter cold; a nut kept warm and dry will simply sit. Move seedlings on when the shoot has expanded two true leaves, keeping the root ball whole. Plant out at three to four metres for a garden tree and six to eight for timber spacing, and do the work while the tree is small, because a transplanted pignut seldom recovers from a damaged taproot. Water in dry spells for the first two seasons and allow leaf litter to accumulate beneath the tree.
The hickory shuckworm tunnels in the husk and causes nuts to drop or shrivel, and clearing fallen husks reduces the population. Hickory bark beetle attacks trees already weakened by drought or root damage, and hickory decline, a canker disease recorded in the eastern states, has killed stands on dry sites; keeping trees vigorous and thinning crowded woodland is the practical defence. The larvae of the regal moth feed on hickory foliage and are harmless to a large tree, though startling to find.
Our Take
Give this tree deep ground, room for its taproot and no further interference, and it will outlive whoever planted it. I grow it beside the shagbark hickory, which yields the nuts worth gathering, and I keep both well away from the black walnut, whose roots and litter suppress so much of what grows near them. Where the ground is richer and you want a nut crop rather than timber, the pecan is the hickory to plant.
Related Reading
Gardeners who grow Pignut Hickory often pair it with these related subjects: