In short
- Needs full sun, warmth and fertile, moist soil.
- Cold-sensitive — plant out only after mid-May.
- Regularly pinching the shoot tips encourages bushy growth.
- The leaves turn bitter after flowering — remove flower buds.
- Grows well in the company of tomatoes.
- Seeds germinate in 5–10 days at 20–25°C; sow directly outdoors only once the soil has warmed to 15–18°C.
- Drying takes away most of the aroma — surplus leaves are better frozen.
- In a container it needs at least 2–3 litres of growing medium per plant and effective drainage.
Botanical data
- Family
- Lamiaceae (Lamiaceae)
- Height
- 0.2–0.6 m
- Width
- 0.2–0.3 m
- Habit
- Upright
- Growth rate
- Fast
- Position
- Full sun
- Soil
- Humus-rich
- pH reaction
- pH 6–7
- Moisture
- Moderate
- Bloom
- July–September
- Hardiness
- USDA 10a–11b
- Propagation
- From seed, From cuttings
Characteristics
An annual herbaceous plant with a four-angled stem and oval, aromatic leaves. Small lipped flowers are arranged in spike-like inflorescences at the shoot tips. Cultivars differ in leaf colour and aroma profile. It reaches 20–60 cm in height and 20–30 cm in width, and grows fast enough that 6–8 weeks usually pass from sowing to the first harvest. The stem is densely branched and, towards the end of the season, becomes slightly woody at the base. The leaves are borne in opposite pairs, each pair set crosswise to the next; commonly described as oval, they are more precisely ovate to ovate-lanceolate and 2–5 cm long (up to twice that in lettuce-leaf types). The blade is slightly cupped and wavy in Genovese and lettuce-leaf types, whereas in bush and Thai types it is flat. The distinguishing feature is the scent released when the blade is rubbed — it comes from the oil glands visible on the underside as tiny dots. The composition of the oil depends on the chemotype: Genovese cultivars are dominated by linalool and eugenol, Thai basil by methyl chavicol, hence its aniseed note. Within the spike-like inflorescences the flowers are clustered in false whorls; they are two-lipped, white to pale violet, and flowering falls in July–September. The fruit is a schizocarp that breaks apart into four one-seeded nutlets, typical of the mint family (Lamiaceae); the small black seeds swell in water, surrounding themselves with mucilage. The plant requires full sun (at least 6 hours a day), shelter from wind, and humus-rich, well-drained soil with a pH of 6.0–7.0 and even moisture. It is exceptionally cold-sensitive — below 10°C growth practically stops and the blades darken; the first frost ends its cultivation.
Popular cultivars
- ‘Genovese’
- The classic Italian cultivar for pesto: large, slightly cupped, dark green leaves with a sweet, clove-like aroma and no aniseed note. It grows compactly and tolerates regular cutting of the shoot tips well.
- ‘Napoletano’
- A lettuce-leaf type with very large, blistered and crinkled leaves, milder in flavour than Genovese. Convenient where the leaves are served whole — in salads and sandwiches.
- ‘Dark Opal’
- A historic cultivar with dark purple leaves and pink-lavender flowers, valued more for its appearance and for flavouring vinegars than for its yield. Some seedlings tend to revert to green colouring.
- ‘Red Rubin’
- An improvement on the purple types, a selection derived from Dark Opal: the leaf colour is darker and more uniform, the leaves are larger and the plants grow more vigorously. Good for herb borders and mixed containers.
- ‘Minette’
- A bush basil with very small leaves, forming a compact ball about 20 cm tall. The best choice for a windowsill and small containers; its aroma differs from that of the Genovese types — sharper and less sweet.
- ‘Siam Queen’
- A Thai-type cultivar: purple stems and inflorescences, a stiff habit and a distinctly aniseed aroma coming from methyl chavicol. It copes better with heat and turns bitter more slowly after flowering, and is intended for Asian cooking.
Growing and care
Watering
Needs regular watering at the base (not on the leaves), in the morning. Sensitive to drying out and cold — wilts when short of water.
Fertilizing
Moderate; too intensive fertilising weakens the leaf aroma.
Planting
Fertile, well-drained, warm soil in full sun; cold-sensitive — do not plant before mid-May.
Pruning
Pinch the shoot tips above a pair of leaves — this encourages bushy growth and delays flowering.
Companion plants
Good companions
A classic culinary companion; some studies suggest that basil may repel thrips and aphids from tomatoes.
Bad companions
Rue releases allelopathic substances that inhibit the growth of basil in its immediate vicinity.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
Yellow or angular (vein-bounded) spots on the upper leaf surface, matched underneath by a grey-violet or brown coating of spores. It differs from powdery mildew, whose white coating sits on the upper surface. It develops in humidity and cool nights and is dangerous to cucumbers, onions and grapevines. The spots are initially light green or yellowing, and their angular, mosaic-like shape arises because the pathogen's spread is halted by the larger leaf veins. The delicate, felt-like coating on the underside (hence the name 'mildew') is the sporulation of the oomycete — best seen in the morning or after a period of high air humidity. Over time the spots turn brown, dry out and merge, the leaf dies prematurely, which weakens the whole plant and lowers the yield. The disease is highly host-specialised: cucumbers and squashes are attacked by Pseudoperonospora cubensis, onion by Peronospora destructor, grapevine by Plasmopara viticola, and lettuce by Bremia lactucae — so infection of one species usually does not spread to unrelated crops.
Grey mouldA grey-brown, fluffy coating of mycelium on flowers, fruit, leaves and shoots, preceded by watery, rotting spots. It attacks weakened and damaged tissue and develops rapidly in humidity and cool conditions and where air circulation is poor. Common on strawberries, begonias, peonies and roses. The coating is characteristically 'mousy' — fluffy and ashy grey, and when the infected tissue is knocked a visible cloud of spores (conidia) puffs up, which is a diagnostic feature of this disease. Infection usually starts in the weakest tissues: fading petals, wounds, hail marks or pest feeding damage, as well as pollen residue settled on the petals. Small, brown, watery spots appear on the flowers and quickly engulf the whole bloom ('flower blight'); from the infected flower the fungus often grows down into the shoot, causing it to constrict and die back. On soft fruit (strawberry, raspberry, grapes, tomato) a watery, browning rot develops, covered with a thick layer of grey, fluffy felt — the berry softens and 'dissolves'. On seedlings and cuttings Botrytis causes basal stem rot and the sudden collapse of plants. In older, dying mycelium and on plant debris hard, black, irregular lumps form — sclerotia (resting bodies), by which the pathogen overwinters in the soil and in plant debris. The disease also shows up after harvest, as a rapidly advancing storage rot of fruit and vegetables.
Root rot (Phytophthora root rot)The disease develops in overly wet, poorly aerated substrate and attacks the roots and the base of the stem. The roots turn brown, rot and lose their bark, which slips off easily, and a dark, watery rot appears at the stem base. The above-ground part wilts, yellows and dies back despite moist soil – a characteristic symptom, because the damaged roots no longer take up water. Especially at risk are houseplants, succulents and cacti (from overwatering), and in the ground conifers, rhododendrons, ericaceous plants and strawberries on waterlogged sites. The process begins inconspicuously at the root hairs and root tips, which darken and disappear, after which the rot advances towards the framework roots and the root collar. Healthy, pale, active roots waste away — what remains is a dark, rusty-brown or blackish, watery mass, and the outer layer of the root bark slips off like a glove, exposing the discoloured central cylinder. In trees and shrubs, infection of the collar and the base of the trunk (stem-base rot) shows as a dark, often streaking patch, sometimes with oozing, and the bark there is moist and sunken; in conifers and rhododendrons, browning and dieback are seen from the bottom or from the centre of the crown while the soil is still moist. Characteristic is the nested (patchy) occurrence of symptoms in the bed — where water and the pathogen accumulate locally. It is worth distinguishing the two causal oomycete genera: Pythium mainly attacks seedlings and fine roots, causing damping-off and root rot in cool, wet substrate, whereas Phytophthora also attacks older, woody plants, framework roots and the collar, more strongly in warmer, water-saturated soil. Key for diagnosis is the contradiction of the symptoms: the plant wilts and looks 'dry', although the substrate is wet — this results from the destruction of the roots, not from a shortage of water.
AphidsSmall (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | None | — |
| Dogs | None | — |
| Cats | None | — |
History and origin
Basil originates from tropical Asia, where it has long held culinary, medicinal and religious significance (in India the holy basil tulsi). It reached Europe via the Middle East in antiquity, becoming a cornerstone of Mediterranean cuisine. The natural range of the species covers tropical Asia and Africa; India is regarded as the main centre of domestication and cultivar selection, and from there the plant spread along trade routes to the Middle East, Egypt and the Mediterranean basin. The religious cult in India, however, concerns a separate though related species — holy basil (Ocimum tenuiflorum, syn. O. sanctum), known as tulsi; it is neither a cultivar nor a form of common basil. The Greeks and Romans knew common basil as a herbal raw material and described it in treatises on medicinal plants. In the Middle Ages and the Renaissance it was grown in monastery and apothecary gardens across Europe — first as a medicine and only later as a seasoning. In the Orthodox countries of the Balkans it has retained a ceremonial role: bunches of basil are used for sprinkling holy water. The culinary career of the species in Western Europe is linked with Liguria, where the Genoese recipe for pesto was written down in the 19th century. In Poland basil was known in herbalism for centuries, but gained mass popularity only after 1989, together with the availability of imported products and the fashion for Italian cuisine.
Uses
For growing in the vegetable and herb garden, in pots on the balcony, windowsill and terrace. The leaves are used fresh as a seasoning; the plant repels some insects. The evidence for this repellent action is, however, inconclusive: the research indications concern above all a reduction in the numbers of thrips and aphids in the vicinity of tomatoes, not the protection of an entire crop. Seed is sown for transplants in March and April, shallowly (about 1 cm), at 20–25°C; seedlings emerge after 5–10 days. Transplants are planted out after mid-May, at a spacing of 20–30 cm; sowing directly outdoors only makes sense once the soil has warmed to 15–18°C. The site should be warm and sheltered — a spot against a south-facing wall or in a tunnel next to tomatoes, with which basil is traditionally combined, works well. Do not plant it in the immediate vicinity of common rue (Ruta graveolens). In containers allow at least 2–3 litres of growing medium per plant and effective drainage, and water at the base, in the morning. Harvesting means cutting whole shoot tips above a pair of leaves once the plant reaches 15–20 cm; no more than one third of the leaf mass is taken at a time. Fresh leaves are added at the end of cooking, because high temperature destroys the essential oil, and any surplus is better frozen than dried. A few plants left to flower provide forage for bees.
Trivia
- The name derives from the Greek “basilikón” — royal.
- Basil is the key ingredient of the Italian pesto alla genovese.
- Basil seeds soaked in water surround themselves with a transparent mucilage — in Indian and Thai cuisine (as sabja or tukmaria) they are added to drinks and desserts.
- Basil from Liguria is protected by an EU designation of origin (Basilico Genovese PDO, registered in 2005) — it covers a defined growing area and method of harvesting.
Frequently asked questions
Why does basil wilt despite watering?
Common causes are cold (basil is sensitive to temperatures below 10°C), overwatering with root rot, or conversely drying out. It needs warmth, sun and even moisture.
How do you harvest basil so it grows more lushly?
Pinch the shoot tips above a pair of leaves rather than pulling off individual leaves from the bottom. This prompts the plant to branch and yields more leaves.
Why does potted basil bought in a shop die quickly?
Shop basil is often many seedlings crowded into a single pot, competing for water and light. It is worth transplanting them apart or growing from seed with proper spacing from the start.
Can basil be propagated from cuttings?
Yes. Shoot tips 8–10 cm long, with the lower leaves removed, root in a glass of water within 1–2 weeks, or straight away in a moist, well-drained growing medium. This is the quickest way to multiply a successful plant, as well as cultivars whose seed is not on sale.
How do you tell leaf blackening caused by cold apart from disease?
Even darkening and a glassy look across the whole blade is cold damage — the most common cause, the same one responsible for wilting despite watering (a cold night on the balcony, storing cut shoots in the fridge). Downy mildew looks different: yellowing bounded by the veins, in angular patches, with a greyish-violet sporulation coating on the underside of the leaf. In that case you need to thin the plants, improve air movement and water only at the base.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- RHS — BasilInstitution / botanical garden
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