The common name of butterfly pea comes from the resemblance the flower has to the insect. However, as beautiful as the flower is, it does not attract butterflies. Though it may not be the best pollinator plant, it is beneficial to have in the garden as a nitrogen-fixer. This means the bacteria associated with the plant has the ability to grab nitrogen gas from the atmosphere. It then converts it to ammonium which plants can uptake for green, leafy growth.
Originating from Southeast Asia and Africa, butterfly pea is commonly used in Thailand, Malaysia, and Vietnam. The colorful flowers, deep lavender blue to violet, are often dried and used as a food dye. Most commonly, butterfly pea dye is used to tint rice both in savory and dessert dishes. The flowers are steeped to color an after-dinner caffeine-free tea blue, made with honey and lemon. The acidity of the lemon enhances the color even further, by creating a deep purple hue. Combined with the edible flower, roselle hibiscus (Hibiscus sabdariffa), the tea turns bright red. The flower dye seems to take on different hues depending on the pH of the additive.
Varying colors of dyes made from butterfly pea. Left to right - unaltered, addition of an acid, addition of hibiscus, addition of a base. Photo credit: Mandy L. Smith
The secret behind the color are the phenolic pigments, anthocyanins. These pigments are responsible for red, orange, blue, purple, and pink colors in plants, and often associated with antioxidant properties. Delphinidin is the key anthocyanin that makes the butterfly pea dye fun to experiment with in the home kitchen or while dining out. In 2021, the FDA approved the commercial use of butterfly pea as a color additive. It is exceptionally heat stable and can be used in a wide range of food and beverage products including sports drinks, ice cream, chewing gum, and yogurt. The plant has become increasingly popular in the nightlife industry, inspiring brilliantly colored signature co*cktails. A green dye can be made from the leaves for more experimentation.
Butterfly pea can be grown as an annual in Pennsylvania. As with other pea family seeds, the butterfly pea has a thick seed coat and needs to soak in warm water for 24 hours. Start indoors six to eight weeks prior to the last frost date of your USDA growing zone. Seeds can be sown directly outdoors after frost, 6 to 8 inches apart. Butterfly pea germinates within 14 to 21 days. It prefers drier conditions, which includes well-drained soil. Select a site that has full sun, at least six to eight hours per day. Ensure that the site has clean soil, away from busy streets, driveways, or other paths where exhaust is used. The vining plants can grow to 3-4 ft. long, therefore a trellis can keep it tidy and avoid any aggressive tendencies. The 2-inch lavender-blue to violet flowers bloom June through August with ovate or lanceolate leaflets on pinnately compound leaves. Pick flowers to use as your own natural food coloring early in the morning after dew has dried.
Grow butterfly pea in your flower garden this year to enhance your soil and to experiment with its colorful, natural dye properties.
