Of the twenty or so species of hickory as yet recognised about half are in cultivation in the British Isles. They are all, save one, natives of eastern N. America. From its two allies, Juglans and Pterocarya, the genus is distinguished by its pith being solid, and not, as in the others, divided into thin transverse plates; and from Juglans in particular by the branched male inflorescences and four-valved fruit. The hickories are large, deciduous trees with pinnate leaves; the leaflets rather wide apart on a common stalk, themselves nearly or quite stalkless. Male flowers mostly in three-branched, slender catkins, produced either at the end of the previous year’s shoots or at the base of the young ones of the current year; whilst the few-flowered, female inflorescence terminates the young shoot. Nut surrounded by a husk, which often thickens and becomes hard by the time the seed is ripe.
Considering their great beauty of foliage and stately habit – and there is scarcely any tree more striking than a well-grown young hickory – this genus is strangely uncommon in gardens. The reason appears to be their dislike of disturbance at the root, which makes them unsuited to ordinary nursery conditions. The frequent transplanting which is practised by good nurserymen to ensure success at the final removal of their stock is, in my experience, worse than useless with hickories. It induces a stunted, ultimately diseased condition, from which, at the best, it takes them long to recover. The great secret with hickories is to get them in their permanent places early. To anyone desirous of trying these fine trees I would recommend the following procedure. The best species to experiment with are C. ovata, cordiformis, glabra, and tomentosa. Nuts of these should be obtained in autumn from a reliable American seedsman as early as possible after they are ripe. During the winter they should be kept in a box of moist earth, either inside or out-of-doors. In spring the nuts may be placed singly in 6. in. pots, in a slightly heated frame or greenhouse. After they have germinated, all that is necessary is to protect them from frost until they are planted out about the end of May, if sufficient progress has been made. Caryas need a deep, loamy soil if they are to thrive permanently. Previous to planting the seedlings out, the ground should be well worked, and it is wise to put a couple together to anticipate failures; afterwards the weaker one can be removed. To avoid accidents each plant or plants should be enclosed by small-meshed wire-netting.
The object of all this trouble is to avoid the destruction of the tap-root, which is inevitable if ordinary nursery treatment be adopted. A young tree in deep loam, undisturbed, and with its tap-root preserved, will be a better tree in ten years than another treated in the ordinary way will be in twenty. This method, although the best, may not always be practicable. If perforce the seedlings have to be grown on for several years before planting in their final positions they should be grown in light soil and transplanted every year or two to induce a fibrous root system. Such trees will be more difficult to establish than they would have been if planted out in their first year of life, but at least are preferable to ones which have not received this attention.