While holy basil is a close relative of culinary basil, its leaves tend to have a purple cast, its flowers are not as large, and it is shorter-lived. This erect multistemmed subshrub grows rapidly to a height of 3 feet and easily propagates itself by seed. Generally, it has a spicier flavor than culinary basil, and is considered a sacred herb to Hindus. Start indoors six weeks prior to the last predicted frost date and cover the seeds lightly with soil because they require light for germination, or direct sow after frost.