Herb Garden Plants: Basil

Botanical Name: Ocimum basilicum (OH-sih-mum bass-IL-ih-kum) 

Family: Lamiaceae (lay-mee-AY-see-ee); mint

History and Etymology: Sweet basil is native to tropical Asia and Africa and has been widely cultivated for thousands of years. In India, basil is sacred in Hindu customs and used in ceremonies and temples. The scientific name, Ocimum basilicum, comes from the Greek name for an aromatic herb (okimom) considered to have royal properties (basilicum). It was first brought to England from India in the 16th century and to colonial America by early colonists. Its folklore is a complex mix of legends and symbols of love, eternal life, and burial rituals. 

Description: Basil varies in size, leaf and flower color, form, and aroma. Leaves are opposite, ovate, green to purple, entire, and 2 inches long. Two-lipped white flowers, ½ inch long, grow on spikes in terminal racemes. Stems are square. Fruits are dark brown nutlets. The essential oil contains methyl chavicol (estragole) and linalool, imparting a sweet taste and floral scent.  

Cultivars:  

• Sweet flavored, large leaf - culinary use:  'Italian Large Leaf', 'Genovese', 'Napoletano', 'Lettuce Leaf', 'Mammoth', 'Nufar'
• Small leaf or dwarf – decorative, culinary use: 'Minette', 'Minimum', 'Spicy Globe', 'Spicy Bush'
• Thai-style basil - Southeast Asian Cuisine: 'Cardinal', 'Queenette', 'Siam Queen'
• Purple Leaf - vinegars, landscape: 'Amethyst', 'Corsican', 'Dark Opal', 'Red Genovese', 'Red Rubin', 'Osmin'  

Plant Type and Hardiness: Annual; hardy only in warmer climates.  

Height and Width: Height is 12 to 24 inches; width is 12 to 24 inches.   

Bloom Color and Time: White, may be pinkish or purple in Thai or purple basil; July to August. 

Light and Soil: Full sun and well-drained soil.

Cultivation: Basil needs warmth to grow well. Sow seed ¼ inch deep outdoors in late spring to early summer after the risk of frost has passed, or start seeds indoors using a heat mat, 6 weeks before planting outside. Seeds germinate in 1 to 2 weeks. Move seedlings outside when night temperatures are above 60°F and daytime temperatures are in the 80's. Space 12 to 18 inches apart for good airflow. Keep plants well-watered. Susceptible to cold and frost, drought, and water stress. Leaf flavor declines after bloom. Pinch out growing tips to retard flowering and to promote branching and leafy growth. Can be grown in containers, both outdoors and indoors under lights.

Companion Planting: Masks tomatoes from thrips and tomato hornworms. Deters egg-laying behavior from some adult pests, including moths and yellow-striped armyworms.

Pollinators: Nectar-bearing flowers attract bees, butterflies, and other pollinators. 'African Blue' basil blooms from summer to fall and has a camphor odor that is attractive to bees and beneficial wasps. 

Some varieties ('African Blue', 'Cardinal', 'Siam Queen', 'Queenette') have ornamental blooms that are very attractive to pollinators. With these varieties, let the flowers develop to benefit these beneficial insects.

Pests and Diseases: Japanese beetles, fungal root rot, fusarium wilt, and downy mildew (DM). To prevent disease, use healthy seeds and resistant varieties, provide air circulation between plants, practice crop rotation and good sanitation, and avoid overhead watering. Discard infested plants promptly; do not add to compost piles. Disease symptoms can appear even on disease-resistant varieties when environmental conditions are favorable and disease pressure is high. Basil is both deer and rabbit-tolerant.

Basil downy mildew (DM), a new destructive disease present in the United States since 2007, is caused by the oomycete Peronaspora. It appears as yellowing leaves and downy sporulation on the underside of leaves. Spores cannot overwinter. DM can return by infected seed, transplants, or wind-dispersed spores. Prior to breeding studies, most sweet basil varieties were very susceptible to DM, red-leaf and lemon basil had moderate disease levels, and spice types were not susceptible.

Resistant (DMR) cultivars (since 2018): O. basilicum Rutgers 'Devotion', 'Obsession', 'Passion', 'Thunderstruck'; Prospera® (Israel); 'Aroma', 'Everleaf'; Amazel Basil® and PestoBesto™ (Proven Winners).  

Fusarium wilt-resistant (FWR) cultivars: O. basilicum 'Nufar', Rutgers 'Obsession' DMR, Prospera®. 

Propagation:  

• Easy to grow from seeds.
• Cuttings are easily rooted in water. Sterile cultivars are from stem cuttings or purchased as transplants.

Harvesting: Harvest the leaves and stems throughout the growing season, before flowers bloom, preferably in the morning. Spread in a shady, dry, well-ventilated place, or on a wire-mesh tray for quick drying. Do not hang in bundles, as leaves dry too slowly and can mold. Leaves deteriorate when temperatures are below 50°F. Store cut basil stems for a few days in a glass of water at room temperature or up to a week in the refrigerator in a plastic bag wrapped in a paper towel. Do not oven-dry as leaves scorch. Chop leaves and freeze in ice cube trays. 

Herbal Uses: Aromatic, cosmetic, culinary, decorative, and landscape. Basil is used for its fragrance in potpourris and sachets, soaps, perfumes, and aromatherapy. It is best used fresh in cooking. It flavors Italian, Mediterranean, and Asian dishes, as well as tomato and pesto sauces, vegetables, meats, fish, poultry, pasta, rice, tomatoes, and eggs. To maintain its fresh taste, add it toward the end of cooking. Basil adds a delicious flavor to salad greens and in teas, cheese, butter, and vinegar. Its various leaf colors and forms make great accents, edging, and borders in the herb or vegetable garden. 

Garden Notes:  

Other species and hybrids: 

• Ocimum x citriodorum, lemon basil: 'Lemon Mrs. Burns'; variegated, non-flowering 'Pesto Perpetuo' and 'Lesbos' (syn. 'Greek Columnar').
• Ocimum americanum, spice basil: 'Blue Spice', 'Spice', 'Lime'.
• Ocimum tenuiflorum, holy basil, is used in India in religious ceremonies and Ayurvedic medicine.
• 'African Blue' basil, non-seeding hybrid ('Dark Opal' x O. kilmandscharicum), has large purple flower spikes with a camphor scent, very attractive to bees, and excellent for bouquets.