Common prickly ash (Zanthoxylum americanum) in fruit, red-brown capsules split to show shiny black seeds

Photo: A. Barra, CC BY-SA 4.0, cropped · Wikimedia Commons

Common Prickly Ash (Toothache Tree)

Scientific name: Zanthoxylum americanum

Also called northern prickly ash, toothache tree, prickly-ash.

A thorny citrus-family thicket shrub, the giant swallowtail's other native host, with lemon-scented leaves and red capsules of shiny black seed.

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Saplings ship bare-root or in a pot, usually 12 to 18 inches tall, in the dormant season, and their height and age are stated here with the price, once available.

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Wildlife valueDrought tolerantHedge or screenRare

Type: Shrub
Mature height: 10–20 ft
USDA zones: 3–8
Growth rate: Medium
Flowers: April
Fruit: Capsules, June to August
First crop: 3 to 5 years
Mature spread: 15 ft
Sun: Full, Part
Soil moisture: Dry, Average
Grows wild in: Rocky ground, rich moist slopes, stream banks, dry uplands, old fields and edges
Native range: 34 states and the District of Columbia, north and west to North Dakota and south to Florida
List all 35
Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Vermont, Virginia, West Virginia, Wisconsin and the District of Columbia
Also recorded, not native, in Maine. See what is native in your state

Hardiness zones Find your zone by ZIP code

Common prickly ash is a thorny, suckering shrub of the citrus family, and every part smells of lemon peel when crushed. With common hoptree it is one of only two woody citrus-family plants native to the Northeast, so giant swallowtail caterpillars depend on the pair. Almost nobody grows it. Chewing the bark or fruit numbs the mouth, which is why Native Americans used it for toothache. Some years the swallowtail caterpillars strip it; let them. Perfect for a hedgerow, a woodland edge or a rocky slope where a butterfly host and a bird thicket are wanted.

Size, growth and what to expect

Common prickly ash grows wild from southwestern Quebec and eastern North Dakota south to Georgia, Alabama, Oklahoma and eastern Kansas, on bluffs, rocky hillsides, open woods and moist ravines. It grows at a medium pace, roughly a foot and a half a year in its youth on an average site, which is the rate our growth estimator uses for it. It reaches 10 to 20 feet high and 10 to 15 feet across, and it spreads into a colony by suckers. The stems carry sharp prickles as long as half an inch.

Flowers open in April on last season's twigs before the leaves. The fruit is a cluster of reddish-brown capsules that split to show one or two shiny black seeds. Butterflies visit the flowers, and the giant swallowtail lays its eggs on the leaves.

How to grow Common Prickly Ash

Common prickly ash grows in full sun or part shade, in almost any soil, moist or dry, clay, rock or limestone; in shade it lives but may not flower or fruit. It makes a thicket that widens in time, so set it 8 feet from a path or wall and 6 feet apart in a hedgerow.

Plant dormant bare-root or potted plants from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the crown at the soil line, put the native soil back in, and keep the mulch clear of the stems. The seed has a hard coat that keeps it dormant. Sow it in fall the week it is collected, a quarter inch deep in a screened bed outdoors, and the winter does the work; seedlings come up in spring. For spring sowing, hold the cleaned seed cold and damp for 120 days first. Even then only about a quarter of the seed sprouts in tests, and nurseries add an acid soak before the chilling.

Water weekly through the first summer if rain is short; after that it fends for itself. Cage seedlings low for the first two winters against rabbits and deer and keep mulch thin near the stems so voles do not nest there. It needs no pruning. Cut suckers at the ground wherever the thicket is not wanted, in gloves.

Growth is moderate. Only female plants carry the red capsules, so plant three to five seedlings to be sure of a male among the females; bees work the flowers. Nothing serious troubles it. The giant swallowtail caterpillars, which look like bird droppings on the leaves, are the point, and the suckering is the thing to watch.

Heights and zones are typical ranges for the species in cultivation; local conditions and seed source shift them.

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