Common Hoptree (Ptelea trifoliata) is a small deciduous tree that can grow to be 4.5 to 6 m tall. It requires shade and grows best in acidic soil. It is prized for its round canopy winged seeds and dark green leaves that change color in fall. Common Hoptree blooms appear from spring to summer. The seeds of this tree can be used to make beer which is how it got its name.
I. Appearance and Characteristics
Ptelea trifoliata, commonly known as common hoptree, wafer ash, stinking ash, and skunk bush, is a species of flowering plant in the citrus family (Rutaceae). It is native to North America, where it is found in Canada, Mexico, and the United States. It is a deciduous shrub or tree, with alternate, trifoliate leaves.
Ptelea trifoliata is a small tree, or often a shrub of a few spreading stems, growing to around 6–8 m (20–26 ft) tall with a broad crown. The bark is reddish brown to gray brown, with short horizontal lenticels (warty corky ridges), becoming slightly scaly, The plant has an unpleasant odor and bitter taste. Branchlets are dark reddish brown, shining, covered with small excrescences. The twigs are slender to moderately stout, brown with deep U-shaped leaf scars, and with short, light brown, fuzzy buds. It has thick fleshy roots.
- Leaves
Its leaves are alternate and compound with three leaflets, dotted with oil glands. The leaflets are sessile, ovate or oblong, 3–5 in (7.6–12.7 cm) long by 2–3 in (5.1–7.6 cm) broad, pointed at the base, entire or serrate, and gradually pointed at the apex. They are feather-veined, with a prominent midrib and primary veins. They come out of the bud conduplicate and very downy. When fully grown the leaves are dark green and shiny above and paler green beneath. In autumn they turn a rusty yellow. The petioles are stout, 6.3–7.6 cm (2.5–3.0 in) long, with an enlarged base. Stipules are absent. The western and southwestern forms have smaller leaves, 5–11 cm (2.0–4.3 in), than the eastern forms 10–18 cm (3.9–7.1 in), an adaptation to the drier climates in the west.
- Flowers
The flowers are small, 1–2 cm (0.39–0.79 in) across, with 4–5 narrow, greenish white petals. The pedicels are downy. The 4- or 5-part calyx is downy and imbricate in bud. The corolla has four or five petals which are white, downy, spreading, hypogynous, and imbricate in bud. The five stamens alternate with the petals. The pistillate flowers bear rudimentary anthers. The filaments are awl-shaped and more-or-less hairy. The anthers are ovate or cordate, two-celled, with cells opening longitudinally. The ovaries are superior, hairy, abortive in the staminate flowers, two to three-celled. The style is short, the stigma 2- or 3-lobed, with two ovules per cell. Fertile and sterile flowers are produced together in terminal, spreading, compound cymes—the sterile being usually fewer and falling after the anther cells mature.
Flowers are produced in May and June. Some find the odor unpleasant but to others the plant has a delicious scent.
- Fruit
The fruit is a round wafer-like papery samara, 2–2.5 cm (0.79–0.98 in) across, light brown, and two-seeded. The fruit ripens in October, and is held on the tree until high winds shake them loose in the early winter.
- Wood
Its wood is yellow brown; heavy, hard, close-grained, satiny. The specific gravity is 0.8319; weight per cubic foot is 51.84 lb (23.51 kg).
II. How to Grow and Care
Sunlight
As an understory plant, hoptree grows best in sunlight that is diffused by tall trees. It thrives in spots that get partial sunlight. It is tolerant of even shadier conditions as well as of spots that get more sunlight if its moisture needs are met. Harsh afternoon sun can scorch its foliage.
Temperature and Humidity
Hop tree is the hardiest member of the citrus family (Rutaceae) and suitable both for cold and warm climates. It is scattered over a large geographic range, growing as far north as zone 3.
High humidity is usually not a problem as long as there is good air flow around the tree, as trapped moisture can foster the spread of fungal diseases.
Watering
The shadier the conditions, the lower the water needs. Hoptree has some drought tolerance after it is established. The soil around young hoptree shrubs should be kept consistently moist. Apply a 2-inch layer of mulch around the base to prevent the soil from drying out too fast.
Soil
Hoptree grows well in a variety of soil types, including sandy, rocky, loamy, and even somewhat slow-draining clay soil. But it prefers loamy soil that is rich in organic matter and has good drainage. Plus, it likes a relatively neutral soil pH.
Fertilizing
If you’ve planted the tree in fertile soil with plenty of organic matter, there is no need to fertilize the tree other than adding a layer of compost or leaf mold around the base every year.
Planting Instructions
It is best planted or transplanted when dormant, either in early spring or late fall. Dig a hole that is at least twice as wide and 6 inches deeper than the tree’s root ball. Position the tree in the planting hole so the top of the root ball is level with the soil. Backfill with the original soil and tamp it down. Water the newly planted tree regularly during the first year after planting—about 1 inch per week in the absence of rain.
Pruning
Dead or broken branches can be removed any time. Pruning to improve the shape of the tree should be done when the plant is dormant. The spreading, multi-stem shape of the tree responds well to hard pruning if you prefer a tidier, more formal look. The tree does tend to sucker, so you may need to remove newly formed stems arising from the ground.
Propagation
Hoptree can be propagated by softwood cuttings or seeds. To take a softwood cutting from the hoptree, wait until early spring when new growth is appearing.
- Choose a stem with no buds or flowers. With sharp, clean pruners, cut a 6-inch piece of stem and remove the lower leaves.
- Dip the cut end into rooting hormone, and plant the cutting 2 inches deep in a pot filled with moist yet well-draining potting soil. Plant more than one cutting in the same pot, as not all of them will survive.
- Keep them indoors or outside in a sheltered area until roots begin to form. When the new plants are strong enough to grow new leaves, plant them in your chosen spot.
How to Grow from Seed
Propagating hoptree from seed is a lengthier and more involved process than using a softwood cutting:
- Allow the seed pods to dry on the tree, then open them up to remove the tiny seeds inside. Place the seeds in a small container with dampened vermiculite and place the container in the refrigerator for three months to cold-stratify the seeds.
- In the spring, remove the seeds from the refrigerator and plant them about 1 inch deep in rich potting soil.
- Put the container in a warm, sunny location and look for germination in three to four weeks.
Overwintering
Hoptree is a native species that is well adapted to winter conditions in its climate range without requiring any protection.
Potting and Repotting
Due to its large size, hoptree is not a good choice for container planting.
Pests and Diseases
Hoptree doesn’t often have issues with plant diseases, though it might occasionally suffer from rust, leaf spot, and treehoppers, unique-looking insects that eat the sap from the tree but rarely do any significant damage.
It’s important to note that the hoptree is home to several types of butterflies, including some quite rare species. The small butterfly caterpillars might munch on the leaves but rarely are there enough of them to do any real damage. Rather than remove them, it’s best to leave them alone and enjoy the butterfly show in the coming months.
III. Types of Hoptree
There are numerous varieties of hoptree that vary slightly in appearance, including:
- Ptelea trifoliata ‘Aurea’: This cultivar features golden leaves that mature to a bright lime green color.
- Ptelea trifoliata ‘Glauca’: This shrub has blue-green leaves that turn yellow in the fall.
- Ptelea trifoliata ‘Fastigiata’: This variety is known for its upright growth habit and is good for narrow spaces.
IV. Uses and Benefits
- Ornamental uses
Hop tree can be planted as part of a natural hedgerow or shelterbelt. Its lustrous leaves, showy seeds, and chestnut brown bark on young stems are attractive enough to warrant a place in a larger shrub bed. It pairs well with showy companions, particularly those with darker foliage, such as purpleleaf sandcherry and chokecherry. In shady locations, you can plant it instead of azalea, rhododendron, ferns, and myrtle.
- Other uses
It has several Native American uses as a seasoning and as an herbal medicine for different ailments.
Numerous cultivars have been developed for ornamental use in parks and gardens. The cultivar ‘Aurea’ with golden leaves has gained the Royal Horticultural Society’s Award of Garden Merit.
German immigrants to Texas in the 19th century used its seeds in place of hops in the beer-making process, lending the species its common name.
