Fraxinus americana

White ash
Oleaceae
Deciduous, Trees

FRAXINUS

Fairly fast-growing trees, most of which tolerate hot summers, cold winters, and many kinds of soil, including alkaline sorts. Chiefly used as street, shade, lawn, and patio shelter trees. In most cases, leaves are divided into leaflets. Male and female flowers (generally inconspicuous, in clusters) grow on separate trees in some species, on the same tree in ­others. In the latter case, flowers are often followed by clusters of single-seeded, winged fruit, often in such abundance that they can be a litter problem. When flowers are on separate trees, you’ll get fruit on female tree only if a male tree grows nearby.

Ash trees are prone to borers. In some parts of California, ash whitefly is a problem; these chalky white, 1/8-in.-long insects colonize in patches on leaf undersides. Outbreaks are usually controlled by natural enemies; avoid spraying with broad-spectrum insecticides, which are likely to wipe out these beneficial predators.

Fraxinus americana

Native to eastern U.S. Grows to 80 ft. or taller; straight trunk and oval-shaped crown to 50 ft. wide. Leaves up to 15 in. long have five to nine dark green, ovalleaflets, paler beneath; turn purplish in fall. Leaf edges burn in hot, windy areas. Regular water.

Male and female flowers are on separate trees, but plants sold are generally seedlings, so you don’t know what you’re getting. If you end up with both male and female trees, you will get a heavy crop of seed; both litter and seedlings can be a problem. Seedless selections include ‘Autumn Applause’, ‘Autumn Purple’, and ‘Royal Purple’, all with exceptionally good, long-lasting purple fall color; ‘Rosehill’, with bronzy red fall color; and ‘Skyline’, an upright, somewhat narrow oval with brown and purple fall color.