Photo: Agnieszka Kwiecień, Nova, CC BY-SA 4.0 · Wikimedia Commons
Common Hoptree (Wafer Ash)
Ptelea trifoliata
Also called wafer ash, hop tree, stinking ash, shrubby trefoil.
A small citrus-family tree for shade or dry rock, one of only two native giant swallowtail hosts in the Northeast; papery wafer fruit hangs all winter.
Wildlife valueTolerates shadeDrought tolerantRare
- Type
- Small tree
- Mature height
- 10–20 ft
- USDA zones
- 4–9
- Growth rate
- Slow
- Sun
- Part · Full · Shade
- Soil moisture
- Average · Dry
210
Common hoptree is a shrub or small tree of the citrus family, native from New York and Ontario west to Kansas and south to Florida and Texas, and here a scattered plant of river bluffs, limestone slopes and sandy thickets. The three-part leaves are glossy and smell strong when crushed; in May and June the branch tips carry clusters of small greenish-white flowers, sweet to some noses and rank to others, that flies, wasps and solitary bees work. An Iowa study counted 109 kinds of visitors. By late summer the female flowers have become flat papery wafers an inch across, one seed inside, brown and hanging on through winter. With prickly ash it is one of only two woody citrus-family plants native to the Northeast, so the giant swallowtail depends on it north of the citrus belt; the tiger swallowtail is listed on it too. Perfect for a dry limestone slope, a woodland edge or the shade under tall trees where a butterfly host is wanted.
It is plain in every season but early summer, which is why it is so seldom grown; even in the Midwest a recent study called it rarely promoted for gardens. Most plants are male or female, the wild ratio about three males to two, so a lone plant may never fruit. It is deer-resistant, an open understory tree in deep shade and a dense bush in sun, and rare enough in Canada, where it clings to Lake Erie beaches, to have been studied as a rare species.
How to grow Common Hoptree
Common hoptree grows in part shade, full sun or deep shade under tall trees, zones 4 through 9, on any well-drained soil from dry rock and sand to moist loam, limestone included. Sun makes it a dense bush, shade an open small tree. It grows 10 to 20 feet tall and about as wide, so set it 8 to 10 feet from a wall or walk, and that far apart in a hedge.
Plant dormant saplings 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 stem. Seed comes in the wafer: pick the clusters in fall when they turn tan and sow whole wafers a quarter inch deep in a screened, mulched bed; winter rots the wing and chills the seed, and seedlings come up in spring. For spring sowing, break the seed out of the wafer, which blocks germination in a refrigerator, and stratify it damp and cold three months. Sow shallow; seed buried an inch and a half down mostly never came up.
Water weekly the first summer if rain is short; after that it takes drought. Deer leave it alone, but cage the base low for two winters against rabbits and keep mulch thin so voles do not nest at the stem. Prune in late winter only to shape it; cut hard in sun, it regrows as a thick bush.
Growth is slow to medium. Most plants are male or female, and males outnumber females, so plant three to five seedlings if you want the wafers, which follow the flowers the same summer and hang until spring. Flies, wasps and small bees pollinate it, not wind. Expect leaf spots in a wet year, nothing worse.
Heights and zones are typical ranges for the species in cultivation; local conditions and seed source shift them.
- Multistem or single stem? Sometimes the trunk is hiding the answer
- Leaf litter, not wood chips, under the canopy
- Native trees and shrubs for butterflies and moths: host plants first, nectar second
- Native trees and shrubs for birds: caterpillars, fruit, mast, nests and winter cover, month by month
- Ten planting mistakes that quietly kill trees
More like this
