Green Alder

Size, growth and what to expect

Green alder grows at a medium pace, about a foot and a half a year in our growth estimator. It makes a spreading, many-stemmed shrub 3 to 14 feet tall, and it can form dense thickets. Its leaves stay green until they drop in fall. Its roots fix 18 to 55 pounds of nitrogen an acre a year.

Slender male catkins hang from the twig tips in May and June, as the leaves unfold, beside small, upright red female catkins. The female catkins turn into small woody cones that ripen from September to November, and the winged seed blows away on the wind. Moose, hares and beavers browse it. Many birds eat its seeds, buds and catkins, and its thickets shelter nesting birds.

It grows wild across the far North of the world. In North America it ranges from Alaska and Greenland south to New England, New York, Pennsylvania and the upper Great Lakes. An outpost grows on Roan Mountain, on the North Carolina and Tennessee line. In the West its Sitka alder form grows south to California, Idaho, Montana and Wyoming.

How to grow Green Alder

Green alder grows in full sun or part shade, but not under a dense canopy. It wants a moist, acid soil, sandy, gravelly or rocky, near some source of water. Set plants 6 feet apart and keep them 8 feet from a wall. At its size it can go within 15 feet of overhead wires.

Saplings ship bare-root or potted. Plant dormant saplings in fall or early spring, in a hole wider than the roots and no deeper, and put the native soil back in. It needs no fertilizer, since its roots fix nitrogen. Much of the seed is often empty or dead, so sow it thickly. Chill it damp in the refrigerator for one to two months, then sow it in spring an eighth of an inch deep and keep it moist. Seed can also go outdoors in fall on moist, bare soil.

Water it weekly through the first summer unless the ground stays moist. It needs no pruning, and a clump cut back in winter or spring sprouts again from the base.

It carries male and female catkins on the same shrub, and the wind carries the pollen. Green alder sets some seed with its own pollen, but most of its seed comes from another plant's pollen, so plant two seedlings from different parents for seed. Like other alders, it can get leaf spots, cankers and powdery mildew.