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The Honolulu Advertiser
Posted on: Friday, June 30, 2006

City's rainbow shower trees a kaleidoscope of floral colors

By Duane Choy

The city adopted the rainbow shower tree as its official tree in 1965. One attraction: It doesn't leave a pile of messy seed pods to clean up.

Advertiser library photo

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During the city and county's centennial celebration, what better subject to discuss than the official city tree, the rainbow shower?

Under Mayor Neal S. Blaisdell, Honolulu adopted the rainbow shower tree as its official tree in 1965.

The city got this one right.

From April to November, walk, jog, run, bike, skate, drive or take TheBus through urban Honolulu and you will be enraptured by the trees' floral explosions, billowing sherbet oranges, reds, creams and yellows.

You can witness this hypnotic visual experience on King Street by McKinley High School, along Kalaniana'ole Highway, the Kapi'olani Community College parking lot and along H-1 Freeway near Moanalua. My favorite shower tree spot is Kapi'olani Park. I have seen countless tourists and locals, young and old, enthralled by the trees. I love when the wind swirls the fallen blossoms into twirling floral waltzes.

The rainbow shower tree (Cassia x nealiae) is a hybrid cross between the golden shower (C. fistula) and the pink and white shower (C. javanica). Because of the genetics involved, no two trees are alike.

There are three named cultivars for the rainbow shower, and Honolulu's "official" rainbow shower is the Wilhelmina Tenney. The tree started life in 1920 as a seedling on Lunalilo Street in Makiki, at the neighbors of the Tenney family. After the tree was propagated, a Tenney daughter, Wilhelmina (1891-1951) gave material to Foster Garden.

The shower tree makes an excellent accent for the home garden (away from the house). It has moderately rapid growth and can reach 40 feet in height. The tree has good drought tolerance and moderate wind tolerance, but can't tolerate salts at all. It will thrive in any well-drained soil and doesn't require heavy pruning. Prune in the fall or winter and remove any dead wood. Tree healer is not usually necessary on the pruned branches. Fertilize at least once a year with KK or B fertilizer. Best of all, because it's a sterile hybrid, it doesn't leave a pile of messy, stinky seed pods to clean up. Air layering is the way to propagate, with branches best at about 1 inch in diameter.

The rainbow shower is designated in the subfamily Caesalpinioideae. Our native legumes, kakalaioa (Caesalpinia bonduc) and the endemic uhiuhi (C. kavaiensis) are in the Caesalpinioideae.

The rainbow shower tree does the city of Honolulu proud as its official arboreal "shaka."

Duane Choy is a consultant for nonprofit organizations involved primarily with environmental missions, and is a Hawai'i native-plant specialist. Reach him at hanahou@ecologyfund.net.

Correction: A photo in a previous version of this story showed a Queen's Hospital white shower tree, not the Wilhelmina Tenney rainbow shower tree described in the caption.