Plant profile: Psoralea pinnata, the Kool Aid bush

Today we have another wonderful article by P. Garden supporter and Potrero Hill resident Josh - click his name to see all his articles. Enjoy!
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Plant Profile: Psoralea pinnata, the Kool Aid bush
Fabaceae Family

A few years ago, I was on a garden tour in San Francisco. As a group of us plant geeks walked down a street, hunting for the address of the next garden, we passed a small tree, or large shrub, covered in a haze of blue flowers. From a distance, it appeared to be a Ceanothus, but as we got closer, we realized that it was a large Psoralea pinnata, the South African shrub pea, or fountain bush. It was definitely popular with the local bees and other pollinators, and was practically buzzing with their activity.


Psoralea pinnata has been grown in gardens since the late 1600’s, when it was introduced to English gardens from seeds brought back from South Africa. Like many South African plants, it thrives in the milder parts of California, where it is safe from frost. The name fountain bush refers to its habit of growing along streams and in wet places in the wild. In cultivation, it does best in well-drained soil, and needs little water once established. It can be pruned after blooming to limit its size, or it can be allowed to grow into a small, elegant tree up to 12 feet tall. The flowers are not very large, but they blanket the ends of the branches in a cloud of color ranging from blue to purple. They look almost like blue moths; in fact, the flower structure is described as ‘papillonaceous’, or butterfly-like, by our botanist friends. When in bloom, the amazing fragrance is similar to grape drink, leading to another common name: the Kool Aid bush.

The Latin name for this plant comes from the Greek word ‘psoraleos’, meaning warty. This refers to the dots that cover the leaves. The species name, ‘pinnata’, refers to the pinnate form of the leaves.

Psoralea pinnata is easy to grow from seed. While small, make sure it gets regular waterings. Once it is larger and planted in the ground, it can do with occasional watering during the dry season. Flowering is best in full sun, although the plant can tolerate some shade. Seedlings can often be found growing near an older plant, and are easily dug up and given to lucky friends.

There is a small kool aid bush in the Pennsylvania Garden, near the bench. It hasn’t bloomed yet, but hopefully this summer we will all be enjoying the scent of grape Kool Aid and watching the bees dancing around this plant.

Update: Photos above show our plant flowering away!

UPDATE December 2015:
After 7 years in the ground and 4 years of drought, this plant grew to 15' tall but very sadly succumbed to the drought in the end and died after years of beautiful flowers and an excellent, evergreen form. I would love to replace it, even though it could not handle extreme drought.