Able to grow in full sun locations that are plagued by poor soils or tough growing conditions where other trees fail, golden rain trees (Koelreuteria spp.) make excellent choices for shade trees. Overall good in windy sites, trees pruned when they are young ensures they develop with a good structure to diminish any losses during thunderstorm winds. For most luxurious growth and flowering, plant them in moist, well-draining soils in a lawn and mow off young seedlings that sprout.
Three species of golden rain tree are noteworthy. The bouganvillea golden rain tree (Koereuteria bipinnata) notoriously produces thousands of seeds from its branches each fall. Panicle golden rain tree (Koelreuteria paniculata) is the most cold-hardy of the trio. The subtropical species called Chinese rain tree or flamegold (Koelreuteria elegans or Koelreuteria formosana) also yields bumper crops of seeds that germinate readily.
These three species of golden rain tree are native to eastern Asia. The bouganvillea golden rain tree is native to warm temperate areas of China that correspond to U.S. Department of Agriculture hardiness zones 6 through 9. Panicle golden rain trees hail from a much broader native range--China, Korea and Japan--and are hardy in USDA zones 5 through 8. Chinese rain trees are native to Taiwan, to subtropical landscapes in USDA zones 9 through 11.
Golden rain trees are winter deciduous trees that mature roughly to 25 to 35 tall. They bear leaves composed of many dark green leaflets. The bouganvillea golden rain tree's leaves are twice-pinnate, meaning its larger leaves have second tiers of branches that bear leaflets. In late summer, these trees produce millions of tiny yellow flowers on wispy clusters on branch tips to make the tree look like a powdery, airy golden "rain" or mass of lace. Following the flowers, papery seed capsules form, first pale green, then ripening to shades of deep salmon-pink or tan and brown. These three-sided, lantern-like capsules persist into winter and at times look like flowers themselves, adding color and texture to the tree's canopy when viewed from a distance.
Golden rain trees provide fast-growing shade to gardens and add floral color in late summer when other popularly grown landscape trees are green. They striking when in full bloom, and the papery seeds provide ornamentation on the tree, and if cut and dried they make floral arrangement fillers. These trees also demonstrate a remarkable tolerance for less than ideal growing conditions, handling drought, wind, heat and an array of nutrient poor and various pH soil types. They are popular for urban areas needing a tough shade or street tree.
The prolific seed production of golden rain trees potentially causes weediness in landscapes, as seedlings sprout all over. Most worrisome are the bouganvillea golden rain tree and the Chinese rain tree, as they attained noxious or invasive weed status in Australia, Florida and Hawaii. Monitor lawns and edges of native ecosystems to eradicate tree seedlings. Even the panicle golden rain tree has tendency to be weedy in some soils and climates in temperate regions, too.
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