Gardening Plants & Flowers Trees

How to Grow and Care for Hoptree

This native shrub is the host plant for the giant swallowtail butterfly.

Hoptree shrub branches with dark green ovate leaflets with small greenish-white flowers

The Spruce / Evgeniya Vlasova

Hoptree is a deciduous shrub or small tree that serves as the principal larval host plant for the giant swallowtail, North America’s largest butterfly. It can be grown in nearly any amount of sunlight, from deep shade to full sun, and in most soil types, as long as the soil drains easily. Native to North America, hoptree prefers mild-to-cool climates and average humidity.

Common Names Hoptree, stinking ash, skunk bush, wafer ash
Botanical Name Ptelea trifoliata
Family Rutaceae
Plant Type Tree, shrub
Mature Size 15–20 ft. tall, 10–20 ft. wide
Sun Exposure Partial, shade, full
Soil Type Well-drained
Soil pH Acidic, neutral, alkaline
Bloom Time Spring
Flower Color Brown, yellow, green, white
Hardiness Zones 3-9 (USDA)
Native Area North America

Hoptree Care

Hoptree is a very versatile shrub that adapts to many different growing conditions and doesn’t require much maintenance to keep it healthy. Here are the main care requirements for growing hoptree: 

  • Plant it in a location with partial sun and good drainage.
  • Water until the plant is established. Afterwards, only water during dry spells.
  • Fertilizer is only needed in nutrient-poor soil.
  • Prune minimally during the winter to remove dead, damaged, or diseased wood.
Hoptree shrub growing as a tree with ovate leaves in wooded area

The Spruce / Evgeniya Vlasova

Hoptree shrub branches with ovate leaflets clumped together

The Spruce / Evgeniya Vlasova

Hoptree shrub with large ovate leaves surrounding cluster of light green flowers closeup

The Spruce / Evgeniya Vlasova

Hoptree shrub with light green papery seed pods hanging from branch closeup

The Spruce / Evgeniya Vlasova

Light

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. However, in some locations, hoptree tolerates full sun.

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.

Water

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.

Temperature and Humidity

Hoptree shrubs tolerate the wide range of temperatures within their growing zones quite well. However, frost and unseasonably cold temperatures potentially damage tender new growth in the spring. Humidity typically isn’t an issue. In very high humidity, good airflow around the shrub helps to prevent fungal diseases.

Fertilizer

Hoptree grows best in organically rich soil but can also thrive in average soil. Usually mixing some compost into the soil around the shrub every spring is sufficient. If you think the soil lacks nutrients, perform a soil test before you apply any fertilizer.

Types of Hoptree

There are numerous varieties of hoptree that vary slightly in appearance, including: 

  • P. trifoliata ‘Aurea’: This cultivar features golden leaves that mature to a bright lime green color. 
  • P. trifoliata ‘Glauca’: This shrub has blue-green leaves that turn yellow in the fall.
  • P. trifoliata ‘Fastigiata’: This variety is known for its upright growth habit and is good for narrow spaces. 

Pruning

Hoptree does not need extensive pruning to keep it looking tidy. If necessary, prune your hoptree over the winter while it’s dormant to clean up its shape. Remove any dead, damaged, or diseased portions as they arise. If you wish to promote more branching, cut back the stems by no more than one-third of their full length just above a leaf node. And to prevent unwanted spread, remove suckers (stems growing up from the base of the plant).

Propagating Hoptree

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.

  1. Choose a stem with no buds or flowers. With sharp, clean pruners, cut a 6-inch piece of stem and remove the lower leaves.
  2. 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.
  3. 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 Hoptree From Seed

Propagating hoptree from seed is a lengthier and more involved process than using a softwood cutting:

  1. 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.
  2. In the spring, remove the seeds from the refrigerator and plant them about 1 inch deep in rich potting soil.
  3. Put the container in a warm, sunny location and look for germination in three to four weeks.

Common Pests & Plant Diseases

Hoptree doesn't often have issues with plant diseases, though it might occasionally suffer from rust, leaf spot, and tree hoppers, 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.

How to Get Hoptree to Bloom

Healthy hoptrees will bloom each year, sending out small clusters of somewhat-stinky flowers that attract a variety of pollinators.

Bloom Months

Hoptree blooms in spring or early summer, usually in May or June. Because hoptree grows in such a wide range of locations (USDA hardiness zones 3-9), its blooming time varies.

What Do Hoptree Flowers Look and Smell Like?

Hoptree's small, greenish-yellow flowers aren't particularly showy but are beloved by pollinators. The flowers can be found in clusters, and the blooms ultimately mature into papery, wafer-like fruits with a single seed. Hoptree flowers do emit a unique scent that some consider lemony but others consider musky and unpleasant.

How to Encourage More Blooms

As hoptree thrives in such a wide range of sun exposures, soil types, and locations, this easy-going tree should flower without issue. If your hoptree is struggling to bloom, evaluate the tree for general health issues.

Caring for Hoptree After It Blooms

Hoptree does not require any particular care after blooming. Continue to care for the tree as you have been. Avoid pruning until it goes dormant in winter.

Deadheading Hoptree Flowers

There is no reason to deadhead hoptree flowers. Removing spent flowers will not inspire significant re-blooming.

FAQ
  • Does hoptree smell bad?

    The flowers, foliage, and bark when crushed give off a musky, slightly lemony odor that some people perceive as malodorous, hence its common names stinking ash and skunk bush. Hoptree is in the citrus family and some people appreciate the intense scent reminiscent of orange-blossoms.

  • What is hoptree used for?

    After the flowers fade, tan, flat 1-inch"wafers", which are actually samaras containing a single seed in each, appear on the tree in June or July. They have a bitter taste and in the past, they were used as a substitute for hops in beer brewing.

  • Is hoptree deer-resistant?

    Hoptree is notably deer-resistant due to its bitter taste and strong smell, Its seeds, however, provide food for birds and other wildlife.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Plant of the Week: Wafer Ash (Hop Tree). University of Arkansas Cooperative Extension Service.

  2. Ptelea trifoliata. North Carolina State Extension.