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Sweet basil

English
  • Vegetables and herbs
Ocimum basilicum
Photo: Jardin botanique de Montréal (Josée Bouthot)
Ocimum basilicum
  • Ocimum basilicum
  • Ocimum basilicum 'Cinnamon'
  • Ocimum basilicum 'Italian Large Leaf'
  • Ocimum basilicum 'Nuphar'
  • Ocimum basilicum 'Purple Ruffles'
  • Ocimum basilicum 'Purple Ruffles'
  • Ocimum basilicum.

Onglets

Botany

Origin and description

Sweet basil is a herbaceous plant native to the tropics. Its leaves grow opposite each other on square stems. The small white, irregular flowers are usually grouped in dense spikes at the tips of the stems. This species, which has been cultivated and selected for thousands of years, includes various taxa that can vary considerably in appearance and flavour. The leaves of lettuce-leaf types can be up to 10 cm long, while those of dwarf basils are often less than 2 cm long. Leaf colours range from pale to dark green, while some cultivars have blue-, purple- or burgundy-tinged foliage. Mature plants can range in height from 15 to 30 cm for dwarf basils to over 90 cm for some cultivars.

The chemical constituents in the essential oil of sweet basil are complex and variable. On the one hand, climate, soil and even harvesting time affect the amount and composition of the oil and hence the leaf flavour. On the other hand, there are a number of chemotypes that are very similar in appearance but have distinctive chemical constituents in their essential oils, and this is reflected in their aromas.

Species, cultivars and related plants

Main cultivars

Sweet basil cultivars have been classified into six categories according to their traditional uses.

Genovese-type basil

This category includes a number of robust plants with a flavour that is a pleasant blend of lemon, mint, cinnamon and liquorice flavour. These are the best types of basil for making pesto.

'Ararat' – Leaves with purple markings; typical flavour with an anise overtone
'Aroma' – Classic form; resistant to fusarium wilt
'Compatto' – Compact plant; grows well in pots
'Envigor' – Large, highly scented leaves; resistant to several viruses
'Fino Verde' – Erect plant; smaller leaves than the type; mildly spicy typical aroma
'Genovese' – Classic form; typical Genovese-type basil aroma
'Gecofure' – Fairly compact plant; resistant to fusarium wilt
'Medinette' – Compact plant; smaller leaves than the type; slow to flower
'Nufar' – Classic form; resistant to fusarium wilt

Lettuce-leaf type basil (“Foglia de Lattuga” type)

This group includes mild-tasting, large-leafed basils well suited to sandwiches and salads. The flavour of these basils has a hint of mint, anise and lemon.

'Grand Vert' – Classic large-leafed form
'Lettuce Leaf' – Very large leaves
'Mammouth' – Very large leaves; resistant to fusarium wilt
'Napolitano' – Large, flavourful, puckered leaves

Spicy basil

These cultivars are often called Thai basil, and have a characteristic anise scent. Spicy basils are used in Thai and Vietnamese cuisine. These attractive plants make a good addition to flower borders.

'Oriental Breeze' – Compact plant; flavourful; lavender flowers surrounded by mauve bracts
'Queenette' – Olive green leaves with a purplish tinge; reddish stems; purple flowers; anise flavour
'Siam Queen' – Compact plant; purple cone-shaped inflorescence
'Spicy Globe' – Compact plant with small leaves; flavourful; plants grown from seed may not be true to type

Lemon basil

This group includes strongly lemon-flavoured basils. They are used in salad dressings for vegetables and seafood. They are also used to flavour beverages and desserts. Many authors consider them to be cultivars of an interspecies hybrid (Ocimum x citriodorum).

'Lesbos' – Erect, compact plant; dark green leaves; bears few flowers
'Mrs. Burns' – Shiny green, highly scented leaves; 50 to 60 cm tall
'Sweet Dani' – Robust and prolific plant; olive green leaves; 75 to 80 cm tall

Dwarf basil

This category includes dwarf cultivars. These are compact plants with small leaves. They can be grown in containers and as a formal element at the front of borders. They are increasingly considered cultivars of an entirely different species (O. minimum).

'Marseilles' – Compact plant (30 cm); leaves slightly larger than the type
'Picollo' – Spicy mint-flavoured leaves with a hint of anise
'Pistou' – Small plant (20 cm); rounded habit; leaves uniformly sized
'Spicy Bush' – Small plant (20 to 30 cm); rounded habit; spicy flavour

Decorative basil

Most of these basils are grown more for their ornamental value than their flavour. Those with coloured leaves are an attractive addition to oils and salads.

'Amethyst Improved' – Dark purple Genovese-type leaves
'Magical Michael' – Compact plant; shiny, olive green leaves; lavender flowers surrounded by burgundy bracts; fruity flavour
'Osmin' – Slightly spicy red leaves fading (turning bronze) during hot spells
'Purple Ruffles' – Robust plant; large, wavy, purple leaves fading (turning bronze) during hot spells
'Cinnamon' – Glossy leaves; mauve flower buds; lavender flowers; delicate fragrance with a hint of cinnamon

Related species and cultivars

Hoary basil, American basil
Ocimum americanum (Synonym: O. canum)

Hoary basil is an erect, bushy plant that grows to 60 cm tall. The stems and leaves are hairy. Spikes of white flowers appear at the stem tips. This plant has a spicy taste, and some chemotypes have a fairly strong camphor scent. It is used to flavour dishes and in traditional medicine.  

Least basil, Peruvian basil
Ocimum campechianum (Synonym: O. micranthum)

Peruvian basil, native to Central America, is an annual plant that grows to over 50 cm tall. Its spicy leaves are used to flavour local dishes. It is also used in traditional medicine.

Holy basil, sacred basil, tulsi
Ocimum tenuiflorum (Synonym: O. sanctum)

Holy basil is a plant with downy stems. Its narrow leaves have hairy petioles. They are green to purple, depending on the cultivar. They are highly aromatic, with a stronger camphor, musky scent than Genovese basils. The small pink flowers surrounded by purple bracts are borne in terminal spikes. This basil is well known in India, where it is used in recipes and traditional medicine.

Blue Spice basil
Ocimum americanum x O. basilicum

This interspecies hybrid has dark green leaves with a metallic sheen. It is used like Genovese style basil for its mild aroma with a hint of anise. The light purple flowers appear late in the season.

Red Rubin basil
Ocimum basilicum x O. forskolei 'Red Rubin'

This interspecies hybrid has attractive cinnamon-flavoured red leaves that retain their colour during hot spells. Compact plant growing 45 cm tall.

Common name

Sweet basil

Latin name (genus)

Ocimum basilicum

English common name

French common name

Botanical family

  • Lamiaceae
Horticulture

Growing conditions

Basil is sensitive to cold. Plant it outdoors after all risk of spring frost is past. Leave 25 to 30 cm between plants.

Basil requires heat and full sun. It does best in slightly acidic soil (pH between 6 and 7) with plenty of organic matter. This genus requires well-drained soil and regular watering, because it does not tolerate over-watering or being allowed to dry out thoroughly. Basil gives good yields in fertile soil. Spread the equivalent of 5 kg/m2 of aged compost at planting time.  

Remove the inflorescences as soon as they appear, as the plant will produce many fewer leaves when in flower. To delay flowering and encourage the growth of new leafy shoots, remove the first two or three pairs of leaves under the inflorescence.

It is best to plant basil in a new site every year to avoid fusarium wilt, a fungal disease that survives in the soil and causes these plants to wilt and die. Avoid poorly drained sites and ideally choose plants that are resistant to the disease or certified fusarium wilt-free.

Propagation

Basil is mainly propagated from seed.

Sow indoors six weeks before the last frost. It is best to sow purple-leaved cultivars 10 to 15 days earlier, because most of them are slow growers. Transplant the seedlings into pots 7 to 10 cm in diameter. The pots may be sown directly in the ground, without removing the seedlings. To encourage bushy growth, remove the terminal shoot once the plant has formed three pairs of leaves. Remove all flowers. Seeds germinate in 5 to 8 days at 22-24oC and remain viable for 8 years.

Use

Culinary uses: “Genovese” and “Foglia de Lattuga” type sweet basils go well with most types of food, especially tomatoes and tomato-based products. Spicy basils are used in Asian cuisine. Lemon-scented ones are used in salad dressings, beverages and desserts. As a general rule, cultivars with coloured leaves are less flavourful, but make good ornamentals and are useful in vinegars and salads.

Harvesting: Young shoots are usually harvested as needed. To avoid premature die-back, keep at least four or five rows of leaves on each stem. It is best to harvest the entire plant at once in fall when temperatures below 5oC are forecast. Handle the leaves carefully, as damaged leaves turn black readily.

Storage: Dried basil loses its flavour quickly, so it is best to use it fresh or frozen.

  • Fresh: Basil keeps for several days in an airtight container stored in the refrigerator vegetable drawer.
  • Frozen: Blanch leaves and freeze them in ice cubes.
  • Dried: Strip the leaves from the stem and spread them out to dry in a warm, dark, well-ventilated location. Once dry, store the leaves in an opaque, airtight container.

See also

Pests and diseases

Fusarium wilt

Root rot and damping off

Impatiens necrotic spot virus

Physiological disorders

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