Fruit Cycle of an English Walnut Tree

English walnut trees are grown for their appearance and their timber, as well as their nuts.

The English walnut (Juglans regia) originated in central Asia--not England--and is also known, less commonly if more accurately, as the Persian walnut. In addition to producing a highly prized hardwood timber, these beautiful trees are famously grown for their edible nuts. The nuts are the largest in the Juglandaceae family, which also includes pecans and hickories. Walnuts have been promoted as a health food since the turn of the 20th century.

Identification

The dense foliage of walnuts consists of compound leaves.

Juglans regia is a deciduous tree that can reach 60 feet at maturity; it grows rapidly, up to 25 feet in 20 years. Its dense foliage boasts compound leaves, consisting of seven to nine smooth-edged, oval-shaped leaves with pointed tips.

Bloom

The catkins are the male flowers of the walnut tree.

Walnuts are monoecious, meaning they have both male and female reproductive organs on the same tree. The drooping flower clusters, known as catkins, are the male--staminate--blossoms; they grow on one-year wood. The female, or pistillate, flowers, on the other hand, grow in pairs or trios on new wood. Walnuts bloom in mid-spring, though the catkins are by far the most observable blooms.

Fertilization

Your walnuts are more likely to be fertile if you have more than one close enough together to be wind-pollinated.

Although this reproductive structure makes walnuts potentially self-fertile, they are also dichogamous, which means that "The time of pollen shedding does not always overlap well with the time of female flower receptivity to pollen," explains University of Georgia botany professor Mark Rieger. Therefore, a second plant is usually required. Walnuts are wind-pollinated; the pollen blows from stamens among the catkins onto the pistils of the smaller flowers, where they develop into ovules.

Fruiting

Before splitting to reveal the familiar nuts, the walnut fruit is fleshy and green.

The fertilized flowers develop into hard, green fruit singly or in small groups of two or three, starting in summer. The fruit develop until autumn; when they are mature, the green flesh splits to reveal wrinkled brown nuts, roughly circular or ovoid in shape and about 1/2 to 2 inches in diameter.

Seeding

Naturally dispersed walnuts can grow to productive trees in 20 years.

Cultivated walnuts are frequently propagated by grafting or budding, but the natural cycle results in the seeds--the nuts themselves--being dispersed to take root as seedlings. Dispersal is typically by the animals who eat them, such as birds and squirrels. To flourish, walnut seedlings require full sun and fine- or medium-textured soil. It will take a seedling approximately 20 years to produce a large crop. In the meantime, the parent tree will continue the cycle, producing new pistillate blooms on each year's new shoots.

References

• University of Georgia: Mark Rieger's Fruit Crop Homepage: Walnuts--Juglans regia
• WalnutsWeb.com: How to Grow English Walnuts
• USDA: Conservation Plant Characteristics for Jugland regia L.
• Missouri Botanical Garden Kemper Center for Home Gardening: Juglans regia

Resources

• Purdue University: Horticulture and Landscape Architecture: Senior Study: Fruits & Nuts
• American Journal of Botany: Genetic Variation in Walnuts..., March 18, 2010