Ocimum × africanum (African Blue Basil)
Ocimum × africanum (African Blue Basil)
Contents
Introduction & History
African Blue basil is a notable sterile hybrid that produces continuously without ever setting viable seed. This unique biology makes it a perennial producer in frost-free climates and eliminates the bolting problem that plagues other basils. Its large, slightly camphoraceous leaves with purple-veined undersides and tall purple flower spikes make it one of the most ornamental and pollinator-friendly basils, with bees visiting its continuously blooming spikes from spring through hard frost.
History & Origin
African Blue basil originated as an accidental hybrid between Ocimum basilicum 'Dark Opal' and O. kilimandscharicum (camphor basil from East Africa) at a US nursery in the late 20th century. The cross is sterile — every African Blue basil plant in the world was vegetatively propagated from the original hybrid or its clones. This sterility is its greatest horticultural advantage.
Botanical Description
African Blue basil is a vigorous, semi-woody perennial growing 60–90 cm tall and 45 cm wide. Leaves are large (5–8 cm), ovate, with a distinctive appearance: green upper surface with pronounced purple veining and purple undersides. Stems are sturdy, square, purple-green. The most striking feature is the continuous production of tall (20–30 cm) purple flower spikes that bloom non-stop because the sterile hybrid cannot set seed.
Stem: Square (quadrangular) — diagnostic for Lamiaceae • Leaves: Opposite, decussate arrangement • Height: 90 cm at maturity • Spread: 45 cm • Foliage: green-purple • Flowers: purple-blue (summer-autumn)
Planting & Cultivation
African Blue basil is ONLY available as transplants or cuttings — it cannot be grown from seed. Purchase plants from herb nurseries or propagate from cuttings. Plant in full sun, spacing 45 cm apart in rich, well-drained soil. It grows much larger than sweet basil and needs more space. In zones 9–11, it can form a substantial sub-shrub over multiple seasons.
| Sun exposure | Full Sun |
| Soil pH | 6.0-7.0 |
| Spacing | 45 cm |
| Seed depth | 3–6 mm (surface-sow if light-dependent germinator) |
| Water needs | Moderate |
| Soil type | Well-drained, humus-rich loam; add perlite or grit for drainage |
Cultivation Details
Lower-maintenance than annual basils because flowering doesn’t diminish leaf quality. However, cutting back by one-third every 4–6 weeks encourages fresh, tender growth. It’s a heavier feeder than sweet basil due to its larger size and continuous growth. Water consistently. In mild climates, it can grow for several years, developing a woody base.
Climate & Hardiness
Frost-tender — damaged below 2°C, killed below -2°C. In USDA zones 9–11, it’s a true perennial. In cold zones (3–7), treat as an annual or bring containers indoors. More cold-sensitive than sweet basil due to tropical African parentage. Thrives in heat and handles humid subtropical conditions well.
USDA zones: 9-11
Minimum temperature: 0°C
Seasonal Care
Spring: In frost-free zones, new growth resumes. Take cuttings. In cold zones, purchase transplants or root saved cuttings. Summer: Continuous flowering and harvesting. Water regularly. Feed every 2–3 weeks. Cut back periodically. Autumn: Take cuttings before frost for indoor overwintering. Winter: Indoor plants need bright light and warmth above 15°C.
Propagation
Vegetative propagation only — no seed exists. Stem cuttings root in 7–10 days — African Blue roots faster than most basils. Each plant can provide dozens of cuttings per season. Layering: pin low stems to soil and they root at nodes in 2–3 weeks.
| Method | Success rate | Time | Notes |
|---|---|---|---|
| Stem cuttings | 70–90% | 2—4 weeks | Softwood in spring, semi-ripe in summer; 8–12 cm |
| Division | 95%+ | Immediate | Split established clumps in spring or autumn |
| Seed | 50–80% | 14–28 days | Some require cold stratification; germination variable |
| Layering | 80–90% | 6–12 weeks | Pin low branch to soil; sever when rooted |
Diseases & Pests
Excellent disease resistance — hybrid vigor provides better resilience than either parent. Fusarium wilt is rare. The continuous flowering attracts beneficial insects that help control aphids naturally. Root rot in waterlogged soil is the main risk. Spider mites can affect indoor overwintering plants.
Culinary Uses
Not a direct substitute for Genovese — the camphor note makes it better in cooked dishes than raw applications. Use in: tomato sauces and stews, grilled vegetable marinades, robust pesto with pine nuts and Parmesan, and herb-rubbed meats. Young leaves are milder and can be used raw in salads.
| Category | Pairing suggestions |
|---|---|
| Poultry | Chicken, turkey, duck |
| Fish | White fish, salmon, prawns |
| Vegetables | Tomatoes, courgettes, aubergine |
| Dairy | Soft cheeses, butter, cream sauces |
Medicinal & Aromatherapy
Essential oil combines linalool (from sweet basil parent) with camphor and 1,8-cineole (from African camphor basil parent). This dual heritage gives it broader antimicrobial activity than sweet basil alone. The camphor component provides mild pain-relieving and decongestant properties.
| Compound | Properties |
|---|---|
| myrcene | herbaceous, earthy |
| linalool | floral |
| geraniol | rose-like |
| citral | lemony |
| apigenin | mild sedative flavonoid |
Container & Companion Growing
Container Growing
Needs a large container — minimum 30 cm diameter. Use rich, well-drained potting mix. Water daily in summer. Feed weekly with dilute fertilizer during active growth. Container plants are easier to move indoors before frost. Prune to 30 cm before bringing inside.
• Minimum pot size: 20–25 cm Ø, 5 L+
• Shallow roots; frequent watering needed
• Use free-draining potting compost with 20–30% perlite or grit
• Ensure drainage holes; stand on pot feet to prevent waterlogging
• Feed with dilute liquid fertiliser (half-strength) every 2–3 weeks in growing season
Companion Planting
One of the best pollinator plants in the herb garden — non-stop flowering provides continuous nectar from spring through frost. Plant near any crop that benefits from pollination. Its large size makes it a good backdrop plant. Avoid planting next to low, shade-sensitive herbs.
| ✓ Good companions | Tomatoes, Peppers, Strawberries, Carrots |
| ✗ Avoid planting with | Fennel, Rue |
Common Mistakes to Avoid
1. Trying to grow from seed — African Blue basil is sterile. 2. Growing in a small pot — it reaches 90 cm. 3. Expecting sweet basil flavor. 4. Discarding plants without taking cuttings — you can’t replace from seed. 5. Not utilizing the flowers — they’re edible and attract pollinators.
Harvesting & Preservation
Harvest stem tips and individual leaves throughout the growing season. The flavor is basil-forward with camphoraceous undertones — more robust than sweet basil. Young tip growth has the best flavor. Use fresh in robust dishes. Freezing preserves the flavor well. The flowers are edible and make attractive garnish.
• Time of day: Early morning, after dew has evaporated but before intense midday heat volatilises essential oils
• Growth stage: Just before flowering, when essential oil concentration peaks. Once flowers open, the plant redirects energy from leaf production
• Season: Summer-Autumn
• Part harvested: Leaves
• Harvest rule: Never remove more than ⅓ of the plant at once; this ensures continued vigorous regrowth
• Technique: Cut stems cleanly above a leaf node with sharp scissors or secateurs. Tearing damages tissue and invites disease
| Method | Process | Shelf life | Best for |
|---|---|---|---|
| Air drying | Tie bundles, hang upside down in warm, dark, airy space | 6–12 months | Most herbs |
| Oven / dehydrator | Spread on trays, 35–45°C until crisp | 6–12 months | Fleshy-leaved herbs |
| Freezing (whole) | Blanch 5s, ice bath, pat dry, freeze flat on tray | 6 months | Basil, chives, parsley |
| Freezing (oil cubes) | Chop fine, pack into ice cube tray, cover with olive oil | 6 months | Any culinary herb |
| Herb salt | Layer herb and coarse salt 1:4, dry and grind | 12+ months | Rosemary, thyme, sage |
| Infused vinegar | Pack jar, cover with warm vinegar, steep 2–4 weeks | 6 months | Tarragon, dill, basil |
| Infused oil | Fill jar with dried herb, cover with oil, steep 4–6 weeks | 3–6 months | Rosemary, thyme, chilli |
Frequently Asked Questions
Why can’t I find African Blue basil seeds?
African Blue basil is a sterile interspecific hybrid — it produces abundant flowers but zero viable seeds. Every plant in existence was propagated vegetatively from the original cross.
Is African Blue basil good for pesto?
It makes a distinctive, more robust pesto with camphor-basil notes. Use young tip leaves for the mildest flavor. The resulting pesto pairs well with grilled meats and roasted vegetables.
How do I keep it alive through winter?
Take 10–15 cm tip cuttings in late summer, root them in water (roots in 7–10 days), then pot up. Keep on the brightest windowsill in a warm room above 15°C.
Seasonal Care Calendar
🌱 Spring (Mar–May)
Water: Moderate
Feeding: Regular feeding
Resumes growth in frost-free zones. Take cuttings. Plant out after frost.
☀️ Summer (Jun–Aug)
Water: Heavy
Feeding: Heavy feeding
Continuous flowering and harvest. Feed every 2–3 weeks. Cut back periodically.
🍂 Autumn (Sep–Nov)
Water: Moderate
Feeding: Light feeding
Take cuttings before frost for indoor overwintering.
❄️ Winter (Dec–Feb)
Water: Light
Feeding: No feeding
Indoor cuttings on bright windowsill. Water sparingly. Growth slows but continues.
African Blue basil is a vigorous sterile hybrid that flowers continuously without setting seed, making it a non-stop producer and exceptional pollinator plant. Available only from cuttings, it grows to 90 cm with ornamental purple-veined leaves. Camphoraceous basil flavor suits robust cooked dishes.
Quick Reference: Ocimum × africanum
Key Principles: Right location, well-drained soil, regular harvesting to promote growth, and appropriate winter protection for tender species.