The Himalayan Indigo (Indigofera heterantha) is a shrub/tree that has not found favor in our American gardens, although it seems to be quite popular, and readily available, in England. There it has enjoyed recognition from the Royal Horticulture Society, winning its esteemed Award of Garden Merit.
I am unsure as to where or when I acquired this plant for my garden. Here, I grow it in almost full shade. It gets a little morning and late evening filtered sunshine. If I grew it in full sun, it would be a tight shrub of about 3 feet tall and wide. In my shady disposition, it is an open somewhat weeping small tree of about 6 feet. In the spring, it has loads of upright racemes of pale pink pea-like flowers. (They would be much darker in full sun, I am sure.)
It is known to rebloom throughout the summer into fall but in my harsh spot, it only throws up a very few flower stems the rest of the season, not worth mentioning, really. If I had a sunny spot, I might try it there, where it might be more of a mound. In some areas it could freeze down to the ground, or you might want to renew it with a cutback to the ground in the spring.
This is one tough little tree. Not only does it grow in extreme dark shade for most of the day and year, this is very dry shade under a mature maple and next to the woodland path fronting tall mature azaleas and tree-form red tips (Photinia fraseri). There is a bit of irrigation that comes close to it, but it really doesn’t get any special water and gets some fertilizer when I fertilize the azaleas.
From what I can determine, this shrub will grow in sun, part shade, and full shade in USDA Zones 5-11. I can attest to its drought and heat tolerance once established. It can be anywhere from 3 to 7 feet tall, and as wide, depending on its growing conditions. It blooms on new growth, so a yearly trimming could help with flowering, although I have never set pruners to branch of my little tree, and it blossoms on.
It appears the English gardeners are ahead of us with this little treasure, which is related to our native Black Locust (Robinia pseudoacacia). It is suggested as an alternative to the butterfly bush (Buddleia) that has proved to be so invasive in Washington State. You will probably have to search out a supplier on line, but it might be time to use this somewhat ethereal sturdy little shrub in your garden. It will most likely be the only one in the neighborhood.
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