How to Grow Basil
'Classic Italian' (Genovese) from Seed
The definitive pesto basil — large, glossy emerald leaves with the warm, sweet, slightly clove-peppery character that is the flavour foundation of Italian cooking, and equally outstanding fresh on pizza, in salads, or in a caprese
There are many types of basil — lemon, Thai, Greek, purple, cinnamon — but when the word "basil" appears in a Western recipe without qualification, it means Genovese. The large-leafed, sweet, warmly aromatic Italian sweet basil is the foundation of pesto alla Genovese, the essential partner for tomatoes in a Caprese, the finishing leaf on a Margherita pizza, and the herb that more than any other defines the flavour architecture of Italian and Mediterranean cooking. 'Classic Italian' is a Genovese-type selection with the large leaves and balanced sweetness that the type is named for — bred for maximum leaf size and minimum bitterness.
Growing basil from seed is more rewarding than buying supermarket plants — the shop-bought varieties are typically grown fast and crowded, stressed before purchase, and prone to rapid collapse. Seed-grown plants have their own properly-developed root systems, grow to a more productive size, and last significantly longer. The keys to success are well understood: warmth for germination (20–25°C), light reaching the seeds (surface sow — do not bury), the pinching technique applied at the right moment, water at the base in the morning only, and protection from cold. Follow these and you can grow outstanding basil from seed on a sunny windowsill year-round or outdoors from June to September.
Quick Facts at a Glance
Plant Type
Tender Annual (H1c)
Sowing Time
Mar–May indoors; year-round on windowsill
Harvest
8–10 weeks from sowing
Position
Warm, sunny; min 15°C at all times
Height
30–45cm when established
Difficulty Rating
2 out of 5 — Easy with the right technique
Understanding the Plant
Ocimum basilicum 'Classic Italian' (Genovese type) is the large-leafed Italian sweet basil selected specifically for the combination of leaf size, sweetness and balanced aromatic character that defines the variety. The flavour compounds responsible for the characteristic basil aroma are primarily linalool (floral, sweet), eugenol (clove-like), and various other monoterpenes — a complex combination that produces the warm, multi-layered sweetness that simple descriptions like "peppery" or "clove-like" never fully capture. Fresh leaves at room temperature release these compounds continuously; torn or bruised leaves release them intensely; heated leaves change their character somewhat, which is why pesto is made cold and basil is added to pizza after baking.
Basil is a frost-tender tropical plant that evolved in warm, humid conditions. In the UK it is grown as a tender annual — it cannot tolerate temperatures below 10°C, and temperatures below 12°C for any sustained period will cause leaf blackening and death. This cold sensitivity is the most important characteristic to understand for UK growing — outdoors only from June, and never in an unheated position.
⚠️ Critical Germination Rule — Light Required
Basil seed is photoblastic — it needs light to trigger germination. Surface sow onto moist compost and cover with only the thinnest possible dusting of fine vermiculite (the seed should still be visible). Burying seed under compost prevents germination. This is the opposite requirement from calendula or bupleurum. With light access and warmth (20–25°C), basil germinates in 7–14 days.
⚠️ Cold is Fatal — Never Below 10°C
Basil cannot survive temperatures below 10°C and is damaged by sustained cold above this threshold. In the UK, this means indoor growing from March to May, planting out only in June when nights are reliably warm, and bringing pot-grown plants back indoors at the first warning of an autumn chill. Do not place on a cold windowsill in winter or leave outdoors after late September. Cold-damaged basil turns black and is not recoverable.
Sowing & Germination
-
Sow indoors from March to May at 20–25°C. Fill small pots or modules with good-quality seed compost. Water thoroughly and allow to drain. Surface scatter seeds — three to five per 7cm pot — and cover with only the finest dusting of vermiculite. Seeds should still be visible. Place on a warm windowsill or heated propagator.
-
Germination in 7–14 days at the right temperature. Move seedlings immediately to a bright, warm position once they sprout. Bright light prevents etiolation (drawn, leggy seedlings). Thin to the strongest one or two seedlings per pot once they have their first true leaves.
-
The Pinch — apply when seedlings have three sets of leaves. This is the most important care step. Pinch out the central growing tip (the very top of the plant's main stem) between finger and thumb. The plant responds by diverting energy to the lower leaf pairs, producing two or more side shoots in place of the single main stem. Repeat this process on each side shoot as they develop to produce a bushy, multi-stemmed plant rather than a single upright stalk. A pinched plant produces significantly more leaf than an unpinched one across its lifetime.
-
Plant out in June only. After hardening off for two weeks, plant outdoors in a warm, sheltered, sunny position once all frost risk has passed and nights are reliably above 12°C. Space 20–25cm apart. In most of the UK this means late May at the absolute earliest, June for confidence. Container-grown plants can be moved to a south-facing outdoor position in June and brought back indoors in September.
Windowsill Growing Year-Round
On a south or west-facing kitchen windowsill with temperatures consistently above 15°C, basil can be grown year-round. Sow a small pot every six to eight weeks for a continuous supply rather than growing one large plant that eventually runs to seed. Winter windowsill growing requires a heated room — conservatories and unheated sunrooms are generally too cold in winter for reliable basil production.
Care Through the Season
Warmth and Sun Essential
Basil needs warmth as much as it needs light — a minimum of six hours of direct sun per day, and temperatures consistently above 15°C. In a poor UK summer, a south-facing greenhouse or conservatory produces significantly better basil than an outdoor position. On a warm windowsill with supplementary grow-light, excellent basil can be produced year-round.
Water at the Base in the Morning
Water deeply at the base of the plant in the morning only — never overhead, and never in the evening. Wet foliage in cool night temperatures creates ideal conditions for downy mildew, the most common basil disease. Allow the top cm of compost to dry slightly between waterings. Over-watering causes root rot; under-watering causes wilting and leaf loss.
Harvest from the Top Downward
Always harvest by removing the top two to four leaves from each stem, cutting just above a pair of leaves. This harvest point encourages two new branches to develop below the cut, maintaining the bushy habit. Never strip a stem bare — always leave two sets of leaves to photosynthesise and fuel recovery. Regular harvesting delays bolting.
Delay Flowering as Long as Possible
When basil produces flower spikes, the leaves become smaller, the plant stops producing new leaf growth, and the flavour of existing leaves diminishes. Remove flower buds as soon as they appear by pinching them off. A well-pinched plant in a warm, sunny position can be kept productive for two to three months before bolting becomes inevitable.
Feeding
Feed container-grown basil with a half-strength balanced liquid fertiliser every two weeks from six weeks after sowing. Over-feeding with a high-nitrogen fertiliser produces lush but diluted-flavour leaves. A balanced feed at half the recommended rate produces the best combination of productivity and flavour intensity.
Pesto — Use Immediately
Genovese basil produces the finest pesto when leaves are harvested at their largest and most aromatic — typically mid-summer. Process immediately after picking; basil oxidises rapidly and turns black on contact with air and heat (which is why pesto is made cold, with olive oil sealing the surface). Store homemade pesto with a layer of olive oil on top to exclude air.
Harvesting & Using
Getting the Most from Your Basil Harvest
When to harvest: Begin harvesting once the plant has at least six sets of leaves. Always cut from the top, just above a leaf pair, leaving at least two sets of leaves below each cut. For pesto, harvest the largest leaves from the centre and outer stems simultaneously to maximise quantity.
Time of day: Morning harvesting, after the dew has dried but before the heat of afternoon, produces the most aromatic leaves. The aromatic oils are most concentrated in cool morning conditions and dissipate slightly in high heat.
Storage: Basil wilts and blackens quickly when refrigerated. Store fresh-cut stems like flowers — in a small jar of water on the kitchen worktop at room temperature. Do not refrigerate. Use within three to five days.
Freezing: Basil can be frozen, but whole frozen leaves turn black. The best approach is to process with olive oil in a food processor first and freeze as ice cubes — retaining flavour without the blackening.
Culinary uses: Fresh leaves torn over pizza after baking; mixed into pasta with olive oil, garlic and Parmesan; blended with pine nuts, garlic, Parmesan and olive oil for pesto; layered with tomato and mozzarella for Caprese; added to salads, sandwiches and soups at the last moment. Always add basil fresh at the end of cooking — prolonged heat destroys the aromatic compounds.
Common Problems & How to Fix Them
| Problem | Likely Cause | What to Do |
|---|---|---|
| Seedlings leggy and pale | Insufficient light or seeds buried too deep | Surface sow — basil needs light to germinate and to develop properly. Move to the brightest available windowsill. Supplement with a small grow light in winter or early spring when natural light is limited. Leggy seedlings are usually unsaveable — sow afresh in better conditions. |
| Black leaves or stem base blackening | Cold damage or downy mildew | Temperatures below 10°C cause irreversible blackening — check the plant's growing environment. Downy mildew (caused by Peronospora belbahrii) causes similar symptoms with a grey fuzz on leaf undersides. Improve airflow, water at the base only, never overhead. Remove affected leaves. Downy mildew-affected plants are generally not recoverable. |
| Wilting despite moist compost | Root rot from overwatering | Allow compost to dry slightly between waterings. Basil roots need air as well as moisture — consistently soggy compost causes root rot. Repot into fresh compost if root rot is suspected, removing affected roots. Ensure pots have drainage holes. |
| Plant bolts to flower quickly | Heat stress, drought, or insufficient pinching | Pinch out flower buds as they appear. Water more consistently. A single prolonged drought or heat event can trigger bolting — once the plant has committed to flowering, leaf production stops. Sow fresh seed every six to eight weeks for continuous supply rather than relying on a single plant. |
| Aphids on growing tips | Common on basil indoors | Inspect growing tips regularly. Knock off with a jet of water or remove by hand. Avoid chemical treatments on a herb you intend to eat. Good airflow and not crowding plants reduces aphid pressure. Introducing a ladybird to an indoor pot occasionally provides effective biological control. |
Plant Specifications
The herb that more than any other defines Italian cooking
Fresh Genovese basil from your own plant — harvested minutes before using, at room temperature, with its aromatic oils fully intact — is so far superior to the supermarket product that the comparison barely makes sense. Surface sow into warmth, pinch at the right moment, water at the base in the morning, keep it in the warmest position you have, and grow a succession of plants every six to eight weeks for a continuous supply through the season. This is kitchen herb growing at its most direct and most rewarding.
Shop Basil Classic Italian Seeds →