Juglans microcarpa Seeds | Texas Black Walnut

Small, round, thick-shelled little walnuts clustered on a slender twig — Texas Black Walnut (*Juglans microcarpa*): Juglandaceae, streams and ravines of Texas, New Mexico and northern Mexico.

LATIN NAME: Juglans microcarpa

COMMON NAME: Texas Black Walnut

Plant Profile

Little walnut is the smallest of the American walnuts, a rounded tree or large shrub of five to ten metres with slender, drooping branchlets and fine pinnate leaves that turn clear yellow in autumn. It grows along streams and in rocky ravines from Texas through New Mexico into northern Mexico, where heat, drought and alkaline ground are the ordinary conditions of life. The nuts are small, thick-shelled and sweet, and the tree is far more important as a rootstock and a breeding parent than as a crop. Its crown is open enough to cast a light, dappled shade rather than a dense one. The leaves are glossy and narrow, with five to nine leaflets, and they hang on slender stalks that move in the wind.

Science & Biotechnology

Juglans microcarpa has been studied mainly for what it can give other walnuts. It carries resistance to several soil-borne problems and tolerates drought, heat, salinity and high pH, and it has been used in breeding programmes seeking rootstocks for the common walnut in irrigated desert orchards. Molecular work confirms it as a distinct diploid species in the black walnut section, closely allied to J. major. Its small genome and short generation time have made it a convenient subject for studies of walnut genetics, and it is one of the parents of several clonal rootstock lines now planted in California. Its nuts are also small enough to be swallowed whole by birds, which is one reason the species moves along watercourses faster than its size suggests.

Uses & Benefits

Its nuts are sweet and well flavoured but too small to be worth cracking in quantity, and the wildlife take most of them anyway. The tree’s practical value is as a rootstock in dry, alkaline country, and as a parent in breeding for stress tolerance. In the garden it is a good small shade tree for a hot, dry site, with fine autumn colour and a graceful, weeping habit, and it holds banks and stream edges where little else will. The wood is dark and hard, but the trees are too small to cut for anything but fuel. The species is also used as a shade tree in pecan orchards on thin soil, where its small size keeps it out of the way.

Growing from Seed

Sow fresh nuts in autumn, or stratify for twelve to sixteen weeks and sow in spring, two to three centimetres deep. Germination is usually reliable and the seedlings are fast for a walnut. Give the young plant full sun and sharp drainage, and water it through the first two summers while the taproot reaches down. It resents waterlogging far more than drought, and it should never be planted in a hollow where winter water stands. Allow five metres for the crown, and prune only to remove dead wood. Mulch around the base to hold moisture, but keep the mulch clear of the trunk itself.

Our Take

A tough little walnut for hot, thin ground, best valued as a rootstock and a parent rather than a nut crop. It will grow where the common walnut sulks.

Tree Seeds