In the dog days of summer, the Arboretum’s Living Collection appears as a verdant sea of foliage. The flowers of spring and early summer are gone and the predominant color in the landscape is green. But there are a few trees producing colorful blossoms right now, one of the most interesting of which is silk tree (Albizia julibrissin). This small to medium sized tree in the pea family (Fabaceae) has a wide native distribution in Asia, ranging from Japan west to the Caspian Sea region. It is hardy to USDA Zone 6 (average annual minimum temperature -10 to 0 degrees F) and many specimens can be seen growing around Boston. Silk tree starts blooming in early July and continues to produce flowers for a good two months. The fragrant flowers feature powderpuff-like domes composed of bright pink, threadlike stamens. Visit the Arboretum to see a number of specimens of the species plus a specimen of the cultivar ‘Ernest Wilson’ [pdf] (it’s slightly hardier than the species) that is blooming on the slope southwest of the Hunnewell Visitor Center.