How to Grow Indigofera Tinctoria

Indigofera tinctoria is the scientific name of true indigo, a plant best known as the source of the blue pigment used to dye denim. It is a flowering leguminous plant grown mainly as a compost element used to impart nitrogen into the soil following periods of intense farming. The 3- to 6-foot-tall spreading growth habit bears pale gray-green foliage and pink flowers, making it appropriate for ornamental usage in U.S. Department of Agriculture zones 5 to 9. True indigo is easy to grow from seeds, like all legumes, but they must only be sown outdoors when air and soil temperatures reach 70 degrees F.

Things You'll Need

• Coffee filter
• Bowl
• Soil pH test kit
• Rotary tiller
• Compost
• Pelletized lime
• Garden hose with adjustable nozzle
• Kelp emulsion

Instructions

1. Harvest seeds from a vigorous, healthy Indigofera tinctoria shrub in late summer. Select several clean, unblemished seedpods and remove them by hand. Store the seedpods until early spring.

2. Place a coffee filter in a clean bowl. Crack open the seedpods over the bowl and shake the seeds onto the coffee filter. Fill the bowl with hot -- but not boiling -- water and soak the seeds for 24 hours.

3. Prepare the planting bed while the seeds soak. Select a planting site with full sun and good drainage. Test the soil acidity using a soil pH test kit. Soil pH below 6.9 will require amendment to increase the alkalinity.

4. Cultivate the soil to a depth of 10 to 12 inches using a rotary tiller. Remove any stones or large rocks from the bed. Spread an 8-inch layer of compost across the bed. Add pelletized lime to the bed according to the manufacturer's instructions if your soil pH is above 6.9. Run the tiller over the bed several more times to incorporate the amendments. Water to an 8-inch depth to settle the soil.

5. Discard any seeds that are floating on the surface of the water. Gather the top of the coffee filter and lift the remaining seeds from the bowl. Allow them to drain for 15 minutes before planting them.

6. Poke one 1/8-inch-deep hole every 12 inches. Sow one seed into each hole and lightly cover with soil. Water the seeds to a depth of 7 inches every 10 days using a garden hose with an adjustable nozzle set to soak. Seedlings will appear after 30 days.

7. Thin the seedlings to one every 3 feet once they reach 6 inches in height and have a set of true leaves. Replace one monthly watering with 1/2 cup of kelp emulsion diluted in 2 gallons of water to provide a good source of additional nutrients.

Tips & Warnings

• Starting Indigofera tinctoria seeds indoors four weeks before the last frost in spring is possible but not recommended due to the sensitivity of the species' root system.

• Wear gloves and goggles when handling pelletized lime.

References

• "Wild Color: The Complete Guide to Making and Using Natural Dyes"; Jenny Dean; 1999