How to Grow Chillies: From Seed to Harvest, Every Variety and Method

Chilli heat is measured in Scoville Heat Units (SHU). A rough guide:

**No heat / very mild (0–2,500 SHU):** • Sweet peppers / bell peppers: 0 SHU • Banana pepper, Pimento: ~500 SHU • Anaheim, Poblano: 1,000–2,500 SHU — excellent for stuffing, roasting

**Mild-Medium (2,500–30,000 SHU):** • Jalapeño (standard): ~8,000 SHU — the most popular home-grow chilli; productive, versatile • Serrano: ~15,000 SHU — hotter jalapeño with more complex flavour • Mirasol / Guajillo: ~5,000 SHU — essential in Mexican cuisine

**Hot (30,000–350,000 SHU):** • Cayenne: ~50,000 SHU — classic drying variety, very productive • Bird's Eye / Thai chilli: ~100,000 SHU — small but prolific • Scotch Bonnet: ~200,000 SHU — fruity and hot, essential in Caribbean cooking • Habanero: ~200,000 SHU — intense fruity heat, multiple colour forms

**Superhot (350,000+ SHU):** • Ghost pepper (Bhut Jolokia): ~1,000,000 SHU • Carolina Reaper, Trinidad Moruga Scorpion: ~2,000,000 SHU

**Best for beginners:** Jalapeño (reliable, fast, prolific), Cayenne (easy, great for drying), or Lemon Drop (Aji Amarillo — fruity, 30,000 SHU, surprisingly easy). **Best for flavour complexity:** Aji Amarillo, Scotch Bonnet, or any Ancho/Mulato for dried use.

Chillies need a long growing season, so in northern climates (UK, northern Europe) starting seeds indoors in January–February is essential for reliable crops. Southern US, Mediterranean and tropical climates allow later starts.

**What you need:** • Seed compost (lower nutrient than multipurpose — high-nitrogen compost can inhibit germination) • Small seed tray or module tray • A heat source (critical for chillies)

**Temperature requirements:** Chilli seeds require warmth to germinate reliably. Optimal soil temperature: 24–28°C. Without consistent warmth, germination is patchy and slow. Solutions: • **Heated propagator** — most reliable; maintains exact temperature (available from £15–50) • **Airing cupboard** — warm and dark; move seedlings to light immediately after germination • **On top of a radiator** — inconsistent but functional; use a thermometer to check soil temperature • **South-facing windowsill in warm room** — adequate in summer months only

**Sowing method:** 1. Fill modules or small pots with moist seed compost. 2. Sow 1–2 seeds per module, 5mm deep. 3. Label clearly — chilli seedlings are nearly identical across species. 4. Cover with a propagator lid or cling film to retain moisture. 5. Place on heat source. Check daily for germination. 6. Germination: 7–21 days at correct temperature; up to 40+ days if too cold. 7. Once germinated, move to the brightest available spot immediately — etiolation (stretching toward light) weakens seedlings quickly.

**Potting up:** Once seedlings have 2–4 true leaves (beyond the initial seed leaves), pot up into 7.5cm pots using multipurpose compost. When roots fill the pot (~4 weeks), pot up again to a 15–20cm pot. Final container size: minimum 10–15 litres for full-sized plants. Larger containers = larger plants = more fruit.

**Compost and feeding:** Use good-quality multipurpose compost. Once plants begin flowering, switch to a high-potassium liquid fertiliser (tomato feed is ideal — the nutrient balance for fruiting is the same) applied weekly. High nitrogen feeds before flowering promote leaf growth at the expense of fruit.

**Watering:** Chillies prefer consistent moisture — waterlogging causes root rot; extreme drying causes blossom drop (flowers fall before setting fruit). The 'lift test' is reliable: lift the pot — if it feels light, water thoroughly until drainage runs from the bottom.

**Pinching out:** Pinching out the growing tip when the plant is 15–20cm tall encourages bushy growth and more branching = more fruit sites. Pinch just above a leaf node.

**Outdoor vs. greenhouse/polytunnel:** Chillies grown outdoors in the UK need a sheltered, warm, south-facing position. They will produce well in a warm summer. A greenhouse or polytunnel adds 4–6 weeks of productive season on each end and dramatically improves reliability. Heated greenhouse: can grow almost any variety to full maturity in the UK.

**When to harvest:** Most chillies can be harvested green (immature) or allowed to ripen to their final colour (red, yellow, orange, etc.). Ripe chillies are fully coloured and slightly soft to the touch. Flavour is typically more complex when fully ripe; heat level varies by variety — some are hotter when green, some when red.

Regular harvesting encourages continued production. A plant that holds ripe fruit for too long redirects energy away from producing new flowers.

**Drying:** • **String drying (ristra):** Thread ripe chillies through their stems with a needle and string. Hang in a warm, dry, airy spot. Takes 3–6 weeks. Beautiful and functional. • **Oven drying:** Halve chillies and dry at 60–70°C for 4–8 hours with the door slightly ajar. Preserve colour and flavour well. • **Dehydrator:** The most consistent results at 60°C for 6–12 hours depending on size and water content.

**Freezing:** Whole fresh chillies freeze excellently. Freeze on a tray first (blast freeze), then bag. No blanching needed. Texture softens on thawing but heat and flavour are preserved perfectly.

**Fermented hot sauce:** Puree fresh chillies with 2–3% of their weight in salt. Pack into a jar, ferment 5–10 days at room temperature until bubbling with lactic acid bacteria. Blend smooth. The result is a complex, deeply flavoured hot sauce far superior to bottled alternatives.

**Overwintering:** Chilli plants are perennials in their tropical native climate. Cut back by two-thirds in autumn, bring indoors to a frost-free location (5–10°C is fine), water very sparingly over winter. In spring, repot into fresh compost, resume watering, and move back to warmth. Overwintered plants start the following season with a mature root system — producing far more fruit much earlier than a plant raised from seed.