Indigofera himalayensis 'SILK ROAD' Himalayan indigo
Indigofera
The Indigofera genus includes over 700 species of shrubs and herbs, mostly found in tropical and subtropical regions of Asia, Africa, and the Americas. Its common name refers to the plant’s historical use in producing natural blue dye known as indigo, especially from the African species Indigofera tinctoria. It was cultivated since ancient times in India, Egypt, and China, playing a key role in trade routes between the East and Europe. Indigo was once so valuable it was nicknamed “blue gold,” and the blue colour became a symbol of wealth – seen in textiles, decorative items, and interior design. As with many valuable and precious commodities, it was also associated with exploitation – from slave labour in America to forced farming in colonial India, even leading to mass farmer uprisings.
Indigofera himalayensis is a species found naturally in the Himalayan mountains, especially in Nepal and northern India, at altitudes around 2,000–3,000 meters. It was first described in 1958 by Pakistani botanist Syed Muhammad Ali in the Swedish journal Botaniska Notiser, published in Lund, known for botanical research. Unlike its mostly African relatives, this species is more cold-resistant, allowing it to be grown in temperate climates, and is valued for its decorative growth and its ability to enrich the soil with nitrogen, benefiting nearby plants. It is still rare in cultivation, which makes it a sought-after species for specialist gardens and collectors.
Silk Road is a horticultural cultivar of the Himalayan indigo selected for its particularly decorative appearance and abundant flowering. It’s been on the market since around 2014. It blooms with vivid pink, small pea-like flowers arranged in upright racemes that open from the bottom up, similar to Liatrs. Flowering begins with the first hot days of June and lasts through July, with flowers appearing on new shoots. Unlike Indigofera heterantha, it does not bloom repeatedly through autumn, but its initial flowering is striking. After blooming, it produces interesting seed pods in short, dark red legumes. The leaves are deciduous, pinnate, resembling miniature acacia or robinia foliage – light to medium green, briefly turning yellow in autumn. It grows quickly into an airy, vase-shaped shrub.
It can be grown in three ways:
I – allowed to grow freely into a prostrate shrub,
II - pruned back in spring by removing 70–80% of branch length to promote dense growth from the base,
III - trained into a multi-stemmed form by selecting 2–4 stronger branches to form the framework. With this method, side shoots are removed to the height where the wide crown is desired. Young plants must be grown in containers and brought indoors for a few winters to protect branches from frost. This allows the wood to mature, and in spring the plant continues growing without losing branch length.
Indigo is easy to grow and doesn’t require much maintenance. For maximum effect, plant it in rich, well-drained soil in full sun. It tolerates poorer soils but may not bloom as much. Mild moisture during the season is better than complete dryness. It works well in prairie or steppe-style compositions, combined with drought-tolerant plants like yucca, albizia, caryopteris, perovskia, echinacea, scabiosa, or gaura. It’s hardy down to about -25°C (USDA zone 6), and possibly lower in well-drained soil, although after a severe winter it might need to regrow from the roots in spring. Mulching is recommended to protect it from temperature swings and excess winter dehydration.
Last update 16-01-2014; 04-08-2025
