Garden PlannerEvidence-aware. Garden with confidence.
Entire healthy mature basil plant in a real garden bed, showing growth habit and scale.Primary identification image. 30–60 cm tall, 30–30 cm wide at maturity.

Basil

Ocimum basilicum L.

Also called: Sweet basil, Genovese basil

Family
Lamiaceae
Season
Warm-season tender annual
Best grown in
Portland, Oregon

A tender, sun-loving herb that grows on the same schedule as tomatoes and is the most-searched companion in the catalog.

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Life cycle & growth stages

  1. 1. SeedSow indoors 4–6 weeks before last frost.
  2. 2. SeedlingEmerges in 5–10 days; needs warmth.
  3. 3. TransplantSet out when nights exceed 10 °C.
  4. 4. Mid-growthPinch tips for bushiness.
  5. 5. HarvestPick leaves and tips all summer.
  6. 6. FloweringWhite flower spikes attract bees; pinch to prolong leaves.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

Start indoors 4–6 weeks before last frost; transplant 2–4 weeks after last frost; direct sow 2–6 weeks after last frost; 50–70 days to maturity from sowing. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

BasilOcimum basilicum
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
BasilFeb 22–Mar 8 (estimate)Apr 19–May 17 (estimate)—Apr 19–May 3 (estimate)May 17–Jun 8 (estimate)Jun 8–Nov 5 (estimate)
  • Start seeds indoors: Feb 22 – Mar 8
  • Transplant outdoors: Apr 19 – May 3
  • Direct sow: Apr 19 – May 17
  • Tend and monitor: May 17 – Jun 8
  • Harvest: Jun 8 – Nov 5

Spacing & support

In-row 25–30 cm; rows 30–45 cm. Planner footprint: 1 cell of 30 cm.

Side-profile diagram of mature basil: canopy 30–60 cm tall, 30–30 cm wide, medium root zone, support and harvest-access envelope.

Soil & water

Soil
Warm, well-drained loam
pH
6–7
Fertility
moderate
Water
Water at the base when the surface dries; avoid wet leaves at night.
Frost
tender; killed by frost

Support & training

No support structure needed.

Basil mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Plants 15–20 cm tall with 3+ leaf pairs
  • Pinch above a leaf pair
  • Harvest before flowering for best flavour
Basil at harvest readiness, showing the visual cues: plants 15–20 cm tall with 3+ leaf pairs; pinch above a leaf pair.

Common problems

Pests: aphids, slugs, Japanese beetle

Diseases: downy mildew, Fusarium wilt

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy basil leaf or fruit and an example of downy mildew.

Container growing

  • Minimum 5 L (20 cm deep)
  • Use quality potting mix and water more frequently
Mature basil in a correctly sized container (5 L or more) with drainage visible.

Companion overview

4 reviewed relationship records (evidence: medium).

Supported or conditional

Tomato

Avoid or separate

None with evidence

Traditional claims only: Pepper.

Full companion profile

Crop rotation

Avoid planting basil or other mint family crops in the same spot for 1 year. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3LamiaceaeOther familyOther familyback after 1+ years

Shared risks in Lamiaceae: downy mildew (basil), root rot in wet soil.

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing basil

Basil is sown indoors 4–6 weeks before the last frost and set out only when nights stay above 10 °C; it blackens at the first hint of frost. Pinch the growing tips above a pair of leaves every week or two to make a bushy plant and delay flowering.

Basil seed beside a ruler or coin for scale.
Basil seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Basil mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Basil and tomato share a season, a sun requirement and a watering rhythm, which is why the pairing works in practice. The field evidence (Bomford 2009) shows the mixture can use land more efficiently than either crop alone at the right density; it found no flavour effect and no magic. Keep basil 30–45 cm from tomato stems so the tomato canopy does not shade it out.

Two or more mature basil plants with a tape measure showing in-row spacing (25–30 cm).
Basil flower detail or bolting stage.
Immature leaves of basil developing on the plant.

Downy mildew is now the main disease in humid regions; resistant cultivars and airflow help. Slugs and Japanese beetles chew leaves.

Edible parts and safety

Edible: leaves, flowers.

Hands or tool harvesting basil correctly (cut, pull, twist or pick) without damaging the plant.

Pests and diseases

Common pests: aphids, slugs, Japanese beetle. Common diseases: downy mildew, Fusarium wilt. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

aphids on basil, with a wider damage-context view.

Timeline

Season timeline for basil: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Feb 22–Mar 8; Transplant outdoors Apr 19–May 3; Direct sow Apr 19–May 17; Tend and monitor May 17–Jun 8; Harvest Jun 8–Nov 5.

Related plants

See also: Lamiaceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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