Ptelea crenulata is a small tree in the citrus family (Rutaceae), endemic to California and native to foothill woodlands, chaparral margins, and riparian corridors of the Sierra Nevada, southern Cascades, and Coast Ranges. It typically reaches 15–25 feet with trifoliate, aromatic leaves and flat, papery samaras that develop through summer and persist into fall. It fits naturally into drought-adapted foothill and woodland gardens without the management demands of non-native trees.
Given its natural habitat at woodland edges, it performs best with afternoon shade on hot inland sites; in coastal conditions it tolerates fuller sun. Water deeply once a week through the first summer to establish roots, then scale back to little or no supplemental irrigation. Minimal pruning suffices-remove crossing or damaged stems in late winter before new growth. It associates well with oaks, coffeeberry, and native ceanothus without crowding them. A layer of coarse organic mulch helps retain soil moisture through dry summers and supports the root system as it extends.
The common name hoptree reflects the historical use of dried Ptelea samaras as a substitute for hops in ale brewing; the fruits share bitter aromatic compounds with true hops. Ptelea species also serve as larval host plants for the giant swallowtail butterfly (Papilio cresphontes), one of the largest butterflies in North America, giving this tree outsized value in a California wildlife garden.
Ecoregions:Northwestern Forested MountainsMediterranean California
These dates are for Zone 6b. Enter your ZIP to time every job to your own frost dates.
- plant · Any time in fallPlant container-grown trees in fall while soil is still warm and autumn rains can support early root establishment.
- watch · Any time in fallCollect mature samaras in late summer to early fall for seed propagation; allow to dry fully before storing in a cool, dry location.
- sow · Any time in winterCold-stratify collected samaras in a moist medium in the refrigerator for 60–90 days before sowing in spring.
- cut · Any time in winterRemove crossing, damaged, or poorly angled branches in late winter before new growth begins.
- sow · Any time in springWater newly planted trees deeply once per week through the first growing season to encourage deep root development.
- watch · Any time in summerInspect foliage in late spring and early summer for giant swallowtail caterpillars; leave them unless numbers are unsustainably high.
- watch · Any time in summerCheck foliage during warm, dry periods for powdery mildew; improve air circulation with selective pruning if it recurs.
- sow · Oct 2 - Nov 13Sow freshly collected seed outdoors in a protected nursery bed or deep pots and leave it to cold stratify naturally; cover with hardware cloth to keep rodents off.
Problems & troubleshooting
Common problems
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Armillaria Root Rot
Thinning, yellowing canopy with progressive dieback; white, fan-shaped mycelial mats visible beneath bark at or just below the soil line; honey-colored mushroom clusters appearing at the trunk base or on surface roots in autumn.
No chemical cure exists. Improve drainage and avoid any injury to roots or trunk. Remove severely infected trees along with as much root material as possible. Do not replant susceptible species in the same spot.