Koelreuteria elegans subsp. formosana: Goldenrain Tree
Edward F. Gilman, Dennis G. Watson, Ryan W. Klein, Andrew K. Koeser, Deborah R. Hilbert and Drew C. McLean
Introduction
Goldenrain tree grows 30 to 40 feet tall with an equal spread, in a broad, somewhat irregular globe-shape. Some trees appear vase-shaped. Although it has a reputation for being weak wooded, it is rarely attacked by pests and grows in a wide range of soils, including high pH soils. Goldenrain tree tolerates dryness and casts little shade because of the open growth habit. It makes a good street or parking lot tree, particularly where overhead or soil space is limited, due to its adaptive abilities. The tree grows moderately and bears large panicles of bright yellow flowers in May (USDA hardiness zone 9) to July (USDA hardiness zone 6) when few other trees bloom. It is not as showy as Koelreuteria bipinnata but is much more cold-tolerant. The seed pods look like brown Chinese lanterns and are held on the tree well into the fall.
Figure 1. Full Form - Koelreuteria elegans subsp. formosana: goldenrain tree Credit: UF/IFAS
UF/IFAS Invasive Assessment Status: caution, may be recommended but manage to prevent escape (Central, South); not considered a problem species at this time, may be recommended (North)
Uses: shade; sidewalk cutout (tree pit); street without sidewalk; specimen; parking lot island < 100 sq ft; parking lot island 100-200 sq ft; parking lot island > 200 sq ft; tree lawn 3-4 feet wide; tree lawn 4-6 feet wide; tree lawn > 6 ft wide; urban tolerant; highway median; reclamation; container or planter
Figure 2. Range
Description
Height: 30 to 40 feet
Spread: 30 to 40 feet
Crown uniformity: irregular
Crown shape: round, vase
Crown density: open
Growth rate: moderate
Texture: coarse
Foliage
Leaf arrangement: alternate
Leaf type: even-pinnately compound, odd-pinnately compound; made up of 7 to 15 leaflets
Leaf margin: lobed, incised, serrate
Leaf shape: ovate, oblong
Leaf venation: pinnate
Leaf type and persistence: deciduous
Leaf blade length: 6 to 18 inches; leaflets are 1 to 4 inches
The root system is coarse with only a few but large roots, so transplant when young or from containers. Do not transplant in the fall as success rate is reportedly limited. Considered a city tolerant tree due to tolerance to air pollution and ability to withstand drought, heat, and alkaline soils. It also tolerates some salt spray but requires well-drained soil. It would be hard to find a more adaptive yellow flowering tree for urban planting. It makes a nice patio tree, creating light shade but its brittle wood can break easily in windy weather.
The tree has only a few branches when it is young and some pruning to increase branchiness helps sell the tree. Prune the tree early to space major branches along the trunk to create a strong branch structure and the tree will be longer-lived and require little maintenance. Dead wood is often present in the canopy and should be removed periodically to maintain a neat appearance. Only single-stemmed trees trained in the nursery with well-spaced branches should be planted along streets and parking lots.
One cultivar is listed: 'Fastigiata'—upright growth habit.
Pests
Occasional attacks by scale may be seen. Sprays of horticultural oil control overwinter stages. Boxelder bug can be a menace.
Diseases
Koelreuteria is subject to few diseases. A canker causes dead and sunken areas on the bark. Coral pink fruiting bodies develop on the diseased bark. Prune out infected branches and fertilize to maintain tree health.
Verticillium wilt attacks Koelreuteria. The disease causes wilting and death of leaves on infected branches. Eventually the entire tree may be killed. Fertilize to stimulate growth. There are no chemical controls
References
Koeser, A. K., Hasing, G., Friedman, M. H., and Irving, R. B. 2015. Trees: North & Central Florida. University of Florida Institute of Food and Agricultural Sciences.
Koeser, A.K., Friedman, M.H., Hasing, G., Finley, H., Schelb, J. 2017. Trees: South Florida and the Keys. University of Florida Institute of Food and Agricultural Sciences.
