How to Grow Woad
Woad (Isatis tinctoria) leaves create a deep blue dye, that is the typical reason for growing this plant. A biennial or short-lived perennial, woad rises in U.S. Department of Agriculture plant hardiness zones 4 through 8 and grows 3 to 4 feet tall. In many regions of the U.S. woad is an invasive grass, so be careful not to let it spread.
Choosing a Site
Woad is a flexible plant which grows in most soils and amounts of light. It can grow in mud and clay soils and loam, and thrives in rich, well-drained soil. Woad tolerates exceptionally alkaline ground, but rises best in a neutral to mildly alkaline ground. Full-sun sites create the most popular plants, however, woad also tolerates partial shade, such as a west- or east-facing garden bed. Woad seldom grows successfully in the exact same site for more than two years because plants deplete the soil of nutrients.
Growing Woad
Growing plants from seed is the typical method for growing woad. After the final frost date, then sow woad seeds where the crops are to grow. Dig up and eliminate weeds in the planting area, and rake the planting site until the soil surface is nice and crumbly. Gently rake in slow-release 12-4-8 fertilizer granules at a speed of 4 tablespoons each 4 square foot, or put on the fertilizer according to the product label. Draw a hoe throughout the ground to twice the depth of this woad seed in rows 24 inches apart. Sow three seeds every 24 inches along each row, and lightly cover the seeds with soil. Water the rows with a gentle spray from a hose.
Caring for Seedlings
Removing competing weeds and watering often promotes healthy woad plants. Eliminate weeds as they seem by pulling out them without disturbing the woad seedlings, and water that the rows regularly so that the soil is continually moist but never waterlogged. When the seedlings have created their second set of leaves, then remove all but the largest, most firmly growing seedling at every sowing site. Allow a space of about 18 inches between each plant. Spread a 2-inch layer of well-rotted manure or compost involving the plants, avoiding the plant stems. Every 3 months while the crops are actively growing, spread slow-release 12-4-8 fertilizer granules evenly within the planting site. Woad seldom suffers from disease or pest problems.
Removing Flowers
Help prevent woad from self-seeding by removing the flowers. Woad causes difficulties with farmers and in natural areas as it spreads quickly by seed in most conditions. Eliminate woad flowers as they fade and before they develop seed pods. Woad usually flowers in the second year, about 20 months after sowing. Sterilize pruning shears by wiping the blades with a cloth soaked in rubbing alcohol, and also prune flowering woad stems in their bases when the flowers wilt. Place the stems in the trash, and sterilize the pruning shears again.