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Basil (Sweet Basil)

Ocimum basilicum

HerbContainer-friendlySummerBeginner Easy

Fast, fragrant, and tender — basil thrives in heat and rewards frequent pinching with bushier growth. Never chill the leaves, keep the soil lean for flavor, and watch for downy mildew.

Growing conditions

Light
Full sun — at least 6 hours of direct light per day, with 8 hours giving the fullest, most flavorful plants
Water
Medium
Soil
Moderately rich, moist, well-drained loam high in organic matter · pH 6.0–6.5 (slightly acidic)
When to sow
Basil is extremely frost-sensitive. Transplant or direct sow only after all danger of frost has passed and night temperatures stay reliably above 10°C (50°F) — typically 1–2 weeks after the last spring frost.
Spacing
20–30 cm (8–12 in) between plants, rows 45 cm (18 in) apart; closer 10 cm (4 in) spacing for cut-leaf harvest
Days to maturity
60–75 days from sowing to first full harvest (cut-leaf baby harvest possible sooner; germination 5–14 days)
Hardiness
Grown as a warm-season annual in all zones (roughly USDA 2–11); a true perennial only in frost-free zones 10–11. Timing keys to your last frost date, not your zone number.

How to grow it

  1. 1

    Start seed warm

    Sow into a moist seed mix and keep it at 21–27°C (70–80°F) to quickly, in about 5–14 days. Basil seedlings hate cold, soggy soil, so give them bright light or a sunny sill once they sprout.

  2. 2

    Harden off and transplant after frost

    Before planting out, off seedlings over 7–10 days by easing them into outdoor sun and wind. only once nights stay above 10°C (50°F) — a single cold night can blacken the leaves. Space plants 20–30 cm (8–12 in) apart so air moves freely between them.

  3. 3

    Thin and feed lightly

    If you direct sowed, thin seedlings to one strong plant every 20–30 cm (8–12 in). Basil is a light feeder: work into the bed at planting and sparingly. Over-feeding with nitrogen grows lush leaves with weaker aroma.

  4. 4

    Water deeply at the base

    Keep the soil evenly moist but never waterlogged; aim for deep water about 2–3 cm (1 in) per week. Water the soil, not the foliage, and water in the morning so leaves dry fast — wet leaves invite downy mildew. A light helps hold moisture and steady soil temperature.

  5. 5

    Pinch and prune for bushiness

    Once a plant has several sets of leaves, out the growing tip just above a leaf pair. The plant branches from below and turns bushy instead of tall and leggy. (harvest) every couple of weeks to keep that cycle going.

  6. 6

    Stop it from bolting

    As summer warms, basil wants to and flower, after which leaf flavor turns bitter. off flower buds the moment you see them to keep the plant making tender leaves. Removing flower spikes this way is the basil version of .

  7. 7

    Succession sow for a long season

    Basil tires by late summer, so start a fresh of plants every 3–4 weeks, or in mid-to-late summer for a fall crop in warm zones. You can also more plants free: a cutting set in water roots in about a week.

Gardener's notes

  • Resistance is the real fix for downy mildew, not spraying — choosing a DMR variety like Prospera up front saves a crop that fungicides rarely rescue once symptoms show.
  • More does not mean more flavor: lean soil and modest feeding concentrate the aromatic oils, while heavy nitrogen grows bland, floppy leaves.
  • Never refrigerate fresh basil — unlike most herbs it's chilling-sensitive and turns black below about 10°C (50°F); keep it at room temperature or freeze it.

Varieties worth knowing

Genovese
The classic large-leaf Italian sweet basil for pesto; benchmark flavor and aroma
Prospera DMR / Prospera Compact DMR (F1)
Genovese-type with strong downy mildew and Fusarium resistance — the most reliable choice where downy mildew strikes; Compact suits containers
Thai (Sweet Thai / 'Queenette')
Anise-clove flavor on purple stems; sturdier in heat and somewhat less prone to downy mildew
Lemon and Lime basil
Citrusy O. basilicum × O. americanum types; noted as less susceptible to downy mildew
Purple basil ('Red Rubin', 'Purple Ruffles')
Ornamental and culinary; red-leaf types show some reduced downy mildew susceptibility
Spicy Globe / Greek (var. minimum)
Tiny-leaved, naturally rounded dwarf — ideal for pots and edging

Common problems & fixes

Basil downy mildew (Peronospora belbahrii)
Sign: Yellowing that spreads from the midrib outward on the upper leaf, with a fuzzy gray-to-purple growth on the underside (look beneath the leaf — it mimics a nutrient deficiency from above)
Fix: Plant resistant varieties such as Prospera DMR or the Rutgers DMR series — the single most effective control. Space widely, water at the soil in the morning, and ensure airflow. Remove and discard infected plants promptly; the spores are wind-borne and spread fast.
Fusarium wilt (Fusarium oxysporum f. sp. basilici)
Sign: Sudden wilting, yellow leaves, and brown streaks in the stem; often one-sided, on plants that were healthy
Fix: Use clean seed and resistant cultivars, and don't replant basil (or rotate it back) into soil where it wilted — the soil-borne fungus persists for years. Remove and destroy affected plants.
Japanese beetles
Sign: Leaves chewed into a lacy, skeletonized pattern, with the beetles feeding in groups on warm days
Fix: Hand-pick beetles in the early morning into soapy water. Avoid lure traps, which tend to attract more beetles than they catch.
Aphids
Sign: Clusters of tiny green or black insects on new growth and leaf undersides, with sticky honeydew and curled tips
Fix: Knock them off with a strong spray of water or treat with insecticidal soap, covering leaf undersides. Encourage ladybugs and other natural predators.
Cold damage / blackening
Sign: Leaves turn black or brown and collapse after a chilly night, even without frost
Fix: This is a disorder, not a disease — basil is injured below about 10°C (50°F). Wait for settled warm weather to plant out, and cover plants if a cold snap threatens.

Companions

Grows well with
TomatoesPeppersOreganoMarigoldLettuceAsparagus
Keep apart from
RueSage (competes for space and prefers drier soil)Fennel

Harvest & storage

Harvest
Begin harvesting once plants are 15–20 cm (6–8 in) tall and well branched, picking from the top down by pinching stems just above a leaf pair to spur regrowth. Harvest in the cool of the morning for the strongest oils, and always before flowering — flavor drops off sharply once a plant bolts. Frequent light harvesting is the best way to keep a plant productive.
Storage
Use fresh for best flavor. To keep a few days, stand stems in a glass of water on the counter (do not refrigerate — basil bruises and blackens in the cold) or wrap loosely in a barely damp towel. For long storage, freeze leaves whole or pureed in oil/water in ice-cube trays, which holds flavor far better than drying; dried basil keeps but loses much of its aroma.

Sources

This guide is curated from authoritative horticulture references — primarily US university Extension services, the USDA, and the RHS.