Photo: A. Barra, CC BY-SA 4.0 · Wikimedia Commons
Common Prickly Ash (Toothache Tree)
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.
Wildlife valueDrought tolerantScreeningRare
- Type
- Shrub
- Mature height
- 10–20 ft
- USDA zones
- 3–7
- Growth rate
- Medium
- Sun
- Full · Part
- Soil moisture
- Average · Dry
210
Common prickly ash is a thorny, suckering shrub of the citrus family, native from Quebec and North Dakota south to Georgia and Oklahoma, in moist ravines, on rocky bluffs and in wood-edge thickets. Every part smells of lemon peel when crushed. Small yellow-green flowers open along last year's twigs in April and May, before the leaves, and bees work them; by late summer the female plants carry clusters of red-brown capsules that split to hang out a single shiny black seed, taken by bobwhite quail, vireos, chipmunks and cottontails. With common hoptree it is one of only two woody citrus-family plants native to the Northeast, so the giant swallowtail depends on the pair for its caterpillars, and it is listed as a possible host of the spicebush swallowtail as well. Perfect for a hedgerow, a woodland edge or a rocky slope where a butterfly host and a bird thicket are wanted.
Almost nobody grows it. Paired prickles up to half an inch long arm the stems, the roots sucker into dense thickets and the Morton Arboretum calls it hard to find in the trade. In Maryland the wild plant is now critically rare, ranked S1 on the state's 2026 rare plant list. Male and female flowers grow on separate plants, so only females fruit. Chewing the bark or fruit numbs the mouth, which is why Native Americans used it for toothache, and some years the swallowtail caterpillars strip it; let them.
How to grow Common Prickly Ash
Common prickly ash grows in full sun or part shade, zones 3 through 7, in almost any soil, moist or dry, clay, rock or limestone; in shade it lives but may not flower or fruit. It stands occasional flooding and drought. Expect 10 to 20 feet tall and 10 to 15 feet wide, and a thicket wider than that 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, crown at the soil line, native soil back in, 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 the Forest Service got only a quarter of it to sprout, 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 both sexes; 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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