Zanthoxylum americanum (northern prickly ash)

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Zanthoxylum, Genus, spp., Multiple species,

Genus
Multiple species

Prickly ashes

Rutaceae

Temperate and subtropical North America, Asia, Africa, and Australasia

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant Fragrant (moderate)

SunFull Sun – Part Shade

WaterMedium · drought-tolerant

HardinessZones 3–10

Overview

Zanthoxylum is a genus of about 225 aromatic, prickly trees and shrubs in the citrus family, Rutaceae, found across temperate and subtropical regions of North America, East Asia, Africa, and Australia. Plants range from suckering shrubs a few feet tall to trees near 50 feet (15 m), armed with paired or scattered prickles on the stems and leaf stalks. The pinnately compound leaves release a citrus-and-pepper scent when crushed. Plants are dioecious, carrying small yellow-green male and female flowers on separate individuals in spring. Several East Asian species, including Z. piperitum and Z. bungeanum, supply Sichuan pepper, the dried fruit husk whose compound hydroxy-alpha-sanshool produces a tingling numbness on the tongue. North American Z. americanum, prickly-ash, is hardy to USDA zone 3 and serves as a larval host for giant swallowtail butterflies. The sharp prickles and the need for both sexes to set fruit are the main constraints for garden use.

Native Range

Native across temperate and subtropical North America, East Asia, Africa, and Australasia, with the greatest number of species in Asia. Z. americanum and Z. clava-herculis are the widespread North American members.

Suggested Uses

Planted as a spiny barrier or hedgerow, in wildlife and butterfly gardens as a swallowtail host, and along woodland edges. Pepper-producing species are grown for their dried fruit husks used as a culinary spice.

How to Identify

Zanthoxylum shows pinnately compound leaves that smell of citrus and pepper when bruised, set on stems guarded by paired spines at the nodes or by scattered prickles along the rachis. Spring flowers are small, yellow-green, and clustered, with male and female on separate plants. Fruits are small dry follicles that split open to reveal one or two shiny black seeds, and the husks of pepper species are reddish-brown and pungent.

Appearance

Size & Dimensions

Height3' - 50'

Width/Spread6' - 30'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~3 weeks

Flowers: April–June

Spring

Small yellow-green flowers open in spring, from about April to June, in axillary or terminal clusters that appear with or just before the leaves. Because plants are dioecious, fruit forms only where male and female individuals grow near one another. Pollinating insects work the modest flowers over roughly three weeks.

Detailed Descriptions

Foliage Description

green, aromatic, yellow in autumn in deciduous species

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5 (Acidic to alkaline)

3579

Soil Types

loam sand clay

Drainagewell drained

Water & Climate

Water Needs

Medium

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Zanthoxylum grows in full sun to light shade in average, well-drained soil and tolerates poor, dry, or rocky ground once established. Cold hardiness ranges widely across the genus, from Z. americanum at USDA zone 3 (-40°F / -40°C) to tropical species held to zone 10. Plants need little feeding and shrug off most pests, aided by their aromatic, spiny growth. Many species sucker from the roots and can form thickets where the shoots are left in place. Watering helps mainly while plants are young, after which most species carry through dry spells.

Pruning

Pruning is done in late winter while plants are dormant, shaping the canopy and clearing crossing or damaged wood. Root suckers can be taken out to hold a single-stemmed form or left to build a thicket. The prickles make heavy pruning slow work.