Hickory Nuts
Shagbark hickory is a large (to 39 m), slow-growing, long-lived deciduous hardwood tree that is native to North America. It produces edible nuts that are consumed by humans and wildlife, and excellent fuel and wood products. C. ovata is distinguished from all other Carya species by the presence of dense tufts of hairs at the tips of the serrations of leaves. Winter buds of C. ovata have conspicuous and persistent dark outer bud scales over the tan, teardrop shaped bud.
Shoots are stout with prominent lenticels and are bulged at the bud scar marking the current season’s growth. Buds are accresant, and swell greatly as growth begins in the spring. The fruit of C. ovata is prominently 4-angled, with the sutures of the husk occurring at the corners of the angles. Shucks are smooth, thick (5-8 mm) and turn rich brown before dehiscing. Nuts are 4-angled, cream colored, thick shelled and have sweet kernels. The bark of young trees is light gray and smooth, but exfoliates in long loose plates on mature trees, giving the tree its common name.
There are three noteworthy varieties of Carya ovata: the autonym var. ovata, var. carolinae-septentrionalis (Ashe) Reveal, and var. mexicana (Manning). Carya ovata var. carolinae-septentrionalis (= C. ovata var. australis (Ashe) Little) has more slender shoots and darker outer bud scales than var. ovata. Hardin and Stone (1984) observed small round scales in var. ovata which were absent from var.
carolinae-septentrionalis and considered that the best leaf characteristic for differentiating the two. C. ovata var. mexicana was described in detail by Manning (1949) who noted that the “Mexican trees are difficult to separate even as a variety”. In general, the shell or internal partitions of the shell are thick, the shell is often only slightly angled, and the husk may be thinner than typical C. ovata, distinguishing the Mexican shagbark hickory as a geographical variety. Some authors also recognize C. ovata variety pubescens, on the basis of extremely dense pubescence on lower leaf surface and twigs, giving the tree the appearance of C. tomentosa. Close observation of the tips of the serrations will reveal tufts of hairs characteristic of C. ovata. There has been at least one named cultivar of this form; ‘Kentucky’.
There are over 130 named cultivars of C. ovata, more than for any other hickory except pecan. Most of the shagbark “cultivars” have not been propagated and may not be worthy of propagation, but are given names in recognition of their selection for nut production. Most of the named cultivars have originated in Iowa, New York, or Ohio, although 22 states and Cana da are represented. Among the most popular current cultivars are ‘Yoder’, ‘Porter’, and ‘Wilcox’.
The diploid shagbark hickory hybridizes with the diploid shellbark hickory [Carya laciniosa (F. Michx.) Loudon] to produce C. X dunbarii Sarg. Several cultivars of this hybrid have been named, including ‘Abundance’ and ‘Weiker’. Carya ovata hybridizes with the diploid bitternut [Carya cordiformis (Wangenh.) K. Koch] to cultivar tests may produce up to 75 lbs. of nuts on 25 year-old trees. Nut weight varies from about 3 g to over 12 g per nut (150 nuts/lb. to 38 nuts/lb.).
The majority of the nut weight is in shell, with the kernel typically accounting for less than 30% of the weight. Outstanding trees have been selected with up to 47% kernel (‘Porter’). Internal shell configuration varies greatly, with kernels on some trees being bound by internal convolutions of the shell, while others produce kernels that easily separate from the shell (‘Wilcox’). As with most hickory species, early nut maturation is attended by severe animal depredation. Seeds have embryo dormancy that is overcome naturally by over-wintering in moist, cool leaf litter or in underground caches of squirrels. Commercially, seed is stratified in moist medium at about 3C (37 F) for 90 to 120 days.
Seed collected from the northern portion of the range requires longer stratification for optimum germination than seed collected from more southerly sources. Germination rates of 50 to 75% are typical. Germination is hypogeal, with initial growth being concentrated in the production of a long taproot. As a result of the excellent anchorage afforded by the taproot, shagbark hickory is rated as wind resistant on most sites.
Shagbark hickory produces prolific sprouts from cut or fire-killed stands with diameters up to 20 to 24 cm. As stump diameters increase stump sprouting decreases and root sprouting increases. The thin bark of young to medium aged trees makes them especially susceptible to damage by fire. Short fire intervals tend to reduce shagbark and favor oak. Hickory wood in general is quite dense, contributing to its value as a fuelwood. Hickory wood furnishes about 25 million BTUs per cord.
The wood of shagbark hickory is among the most dense in the genus, with an average specific gravity of 0.72. Pignut hickory (C. glabra), pecan (C. illinoinensis), and nutmeg hickory (C. myristiciformis) have average specific gravity of 0.75, 0.66, and 0.60, respectively. The sapwood (often sold as ‘white hickory’) is cream to white in color and is preferred over the heartwood, which is pink or red to brown (known in commerce as ‘red hickory’. The wood has high toughness, bending, stiffness, and crushing strengths, and has exceptional shock resistance. It submits well to steam bending, is generally difficult to machine, and has a moderate blunting effect on tools.
Although difficult to glue, it stains and polishes very well. The wood is considered non-durable, with sapwood being liable to attack by the powder post beetle and heartwood being moderately resistant to preservation treatment. Hickory wood is ideal for handles of striking tools such as hammers, picks and axes. It is used for chairs and as ladder rungs. Hickory wood is used extensively for sports equipment such as golf clubs, lacrosse sticks, baseball bats, longbows, and for laminae in racquets and skis. The wood is used for plywood faces and is sliced for decorative veneers. Strips of inner hickory bark are pliable when green, and can be woven to make chair seats.
Shagbark hickory nuts are a valuable food for wildlife. They are a preferred food of squirrels and constitute 5 to 10% of the diet of eastern chipmunks. In addition, raccoons, black bears, gray and red foxes, rabbits, and white-footed mice eat them. Bird species such as mallards, wood ducks, turkeys, and bobwhites also consume shagbark nuts. Humans prefer the nuts of shagbark hickory to most hickory nuts (except pecan). Shagbark is listed in several references as first being cultivated in 1911. However, in 1792 William Bartram reported “ancient cultivated fields” of hickory west of Augusta, Georgia;
“Though these are natives of the forest, yet they thrive better, and are more fruitful, in cultivated plantations, and the fruit is in great estimation with the present generation of Indians, particularly juglans exaltata, commonly called shell­barked hiccory*. The Creeks store up the last in their towns. I have seen above an hundred bushels of these nuts belonging to one family.
They pound them to pieces, and then cast them into boiling water, which, after passing through fine strainers, preserves the most oily part of the liquid; this they call by a name which signifies hiccory milk; it is as sweet and rich as fresh cream, and is an ingredient is most of their cookery, especially homony and corn cakes” Sargent suggested that Juglans exaltata is a synonym of C. alba Nutt. (=C. ovata (Mill.) K. Koch). “Shellbark hickory” was used for C. ovata (Mill.) K. Koch during Bartram’s time, rather than for C. laciniosa as is current. C. ovata is more widely distributed in northern Georgia than is C. laciniosa. It is probable that Bartram was referring to C. ovata.
Bringhurst (1983) outlined 4 steps usually followed in the development of improved fruit crops from wild species. First, superior phenotypes are identified in natural populations. Second, the best selections are propagated in an agricultural setting. Third cultural practices are developed that enhance performance of selected cultivars. Finally, the best selections are crossed pollinated, followed by selection of superior offspring (which are used as parents for further crosses).
Despite their long history of utilization, the shagbark hickory is still at an early stage of crop development. Many “superior phenotypes” have been found in native populations, with nut characteristics being the primary basis of evaluation. The characteristics and performance of these “cultivars” following asexual propagation has been the focus of much attention in the horticultural literature. Unfortunately, such horticultural observations are often based on one tree of a cultivar, often with a rootstock of another species and growing on mediocre sites. We need to integrate nut selection with selection for improved wood production (requiring insect and disease resistance for both), within the context of geographically and edaphically adapted populations grown under realistic cultural systems.
Shagbark Hickory:
The Shagbark Hickory tree, Carya ovata, has a distinctive, shaggy bark, conspicuous on tall straight trees, which gives this species its name. It grows well in both wet and dry areas, but prefers well-drained soils. Shellbark hickory trees are also called shagbark hickory, bigleaf shagbark hickory, kingnut, big shellbark, bottom shellbark, thick shellbark, and western shellbark, which attest to some of its characteristics. It is a slow-growing long-lived tree. The nuts, largest of all hickory nuts, are sweet and edible. Wildlife and people harvest most of them; those remaining produce seedling trees readily. The wood is hard, heavy, strong, and very flexible, making it a favored wood for tool handles. The wood also makes excellent firewood, and often is used in smoking meat. As with other edible nuts, squirrels compete with humans for this fruit. Its bold-textured, jagged branch structure and thick twigs give it a striking appearance in winter. This deciduous shade tree has a yellow fall colour.
Shellbark Hickory:
The Shellbark Hickory tree, Carya laciniosa, is also know as bigleaf shagbark, kingnut, big shellbark, bottom shellbark, thick shellbark and western shellbark). This deciduous tree is similar to that of the Shagbark Hickory, but often not quite as shaggy. The fruit is larger than other hickories. This is a big tree and it prefers wet, fertile bottomland. It is less common than either the Shagbark or Bitternut Hickories. The wood is similar to that of the Shagbark Hickory and is used in much the same way. Its sweet, huge nuts are relished by squirrels and give it an alternative common name of King Nut Hickory, due to their being the largest of the hickories. Like other hickories, it is very tolerant of summer drought. The nuts of shellbark hickory are utilized by wildlife (ducks, quail, wild turkeys, squirrels, chipmunks, deer, foxes, raccoons, and white-footed mice) and man. This tall shade tree displays a yellow fall colour.
Pignut Hickory:
The Pignut Hickory tree, Carya glabra, has medium green broad, flat leaves and firm, gray bark. The bark may be marked in a sort of diamond pattern by shallow furrows and narrow ridges. This tree grows well in fairly rich, well drained to dry soils. It occurs with other hickories and with oaks, characteristically on hillsides and ridges. Pignut Hickory trees, as with other hickories, has wood that is tough and strong. The nuts of this particular hickory, unlike some of the others, are bitter and scarcely edible. The nuts they are an important food for squirrels and chipmunks and other wildlife. This shade tree turns a bright yellow for great fall colour.
Bitternut Hickory:
The Bittenut Hickory, Carya cordiformis, is also known as the Yellow-bud Hickory tree. The yellow bud makes it difficult to mistake for another species and combined with the alternate compound leaves and relatively large nuts, it is very distinctive. The nuts are reported to be bitter, as one of the common names suggests. The lighter colored shallow cracks in the younger bark are roughly similar to those of young Shagbark Hickory, but the mature bark of Yellow-bud Hickory does not split so deeply. This deciduous tree is found on moist, fertile soils in the east and central U. S. and is intolerant of shade. Bitternut Hickory trees are known for their hard wood. The wood is used for pulpwood and furniture. This deciduous species displays a leaf color of medium green to dark green. The fall colour is often green to chartruese, but sometimes is a brilliant golden-yellow in excellent seasons. It is a fast growing, adaptable tree.
Author:
LJ Grauke , Research Horticulturist and Curator
