When Does the Aspen Tree Leaf in the Spring?

Leaf Description

• Aspens get their name from their deep green, glossy leaves that rustle and rattle with the slightest breeze. The fluttering is enabled by their thin, flat stalks. The leaves, shaped like a rounded-triangle, sometimes nearly round, may vary from tree to tree and turn golden yellow in autumn.

Leaf Arrival

• Slim, drooping cylinders of flowers that do not have petals, called catkins, must mature before aspen leaves begin growing. Aspens are dioecious, meaning trees yield either male and female flowers, not both. The flower catkins take four to six weeks to mature before leaves begin to show. The first leaves will typically appear from early May to June. The growth of flower catkins and the subsequent appearance of leaves depends on the sex of the tree and where you live. Female trees flower and grow leaves before male trees. Flowering is triggered by sustained temperatures above 54 degrees Fahrenheit, so climate is a factor. The appearance of catkins followed by leaves occurs in mid-March to April in New England and from May to June in the central Rocky Mountains. At high elevations, aspens may grow flower catkins before the snow melts. The arrival of leaves may also vary between individual stands of aspen, called clones, that grow in the same climate.

Leaf Development

• In their first year of growth, aspen seedlings are lanceolate, a botanical term meaning they are long and slender. The leaf petioles, or stems, are round, not flat. During their second year of growth, aspen leaves widen into their typical rounded-triangle shape and their stems flatten, leading to their characteristic quaking in the breeze.

Leaf Difference

• Quaking aspens form stands or groves called clones that are connected by a single system of shallow roots. All trees in an aspen clone are either male or female and are connected to a single parent. Short-lived aspen clones east of the Rocky Mountains cover no more than a few acres. Aspen clones in the Great Lakes live 50 to 60 years, although a Minnesota clone is 8,000 years old. Clones in the west are larger and live up to 150 years. Pando, a male clone in Utah’s Wasatch Mountains, includes 40,000 trees covering more than 106 acres and is estimated to be 1 million years old, according to the U.S. Forest Service. Weighing an estimated 13 million pounds, Pando is thought to be the largest single living organism in the world. Not only does the arrival of leaves vary between clones, trees in different parts of a single clone may vary slightly, including the size and shape of their leaves.