Growing Chillies in Scotland: The Complete Guide

Capsicum annuum, C. frutescens or C. chinense (species varies by variety)

Chillies need heat and sunshine to fruit well, and a greenhouse, polytunnel or sunny conservatory is the reliable route to a crop in Scotland. Outdoors, they need a sheltered, sun-baked spot.

Chillies ask for the same conditions as sweet peppers: heat, humidity and lots of sun. What chillies add on top is a wide spread of heat levels between varieties, from 5,000 to 1 million Scoville units among the AGMThe RHS's Award of Garden Merit: a UK-wide trials award for reliable performance, not a Scotland-specific recommendation. Full definition → picks.

Preparing the ground

If growing in the ground, use well-drained, fertile, moisture-retentive soil, working in a few bucketfuls of garden compost or well-rotted manure if it's poor or heavy, or mulchingA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition → the surface for a no-digA growing method that avoids turning the soil over, building fertility instead by adding organic matter on the surface. Full definition → bed. In containers, use a pot at least 22cm wide for one plant, or three plants to a standard growing bag, in peat-freeCompost made without peat, which is harvested from a slow-forming, carbon-storing wetland habitat that peat extraction damages. Full definition → multi-purpose compost. Whichever route you choose, this is a crop best grown under cover here, so it's worth preparing the greenhouse border or bags properly rather than treating them as a temporary stopgap.

Sowing

Sow indoors from late winter to mid-spring, with a heated propagator for the earliest sowings. Seed needs about 21°C to germinateA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition →; an early start gives an earlier and longer harvest. Move seedlings to 16-18°C in bright light once through, potting onMoving a plant into a larger pot as its roots fill the current one, giving it more room and fresh compost before it becomes pot-bound. Full definition → progressively, ending in a 13cm pot before planting out.

Plant Pot Sizes: Litres to CM Conversion → has the full table if you're working from litre sizes rather than centimetres at any stage of potting on.

Planting

Plant out once night-time temperatures are reliably at least 12°C, usually late May or early June, after hardening offGradually getting young plants raised indoors used to outdoor conditions over 7–14 days before planting out, so cold, wind and direct sun don't shock or damage them. Full definition → for two to three weeks. Space plants 38-45cm apart, or 30cm for dwarf varieties; a slightly wider 45cm with 60cm between rows is given in Gardener's World for the same crop. Position in the sunniest spot in the greenhouse for the best flavour.

Varieties

All three varieties below carry the RHS Award of Garden Merit, a UK-wide award rather than a Scottish one.

RHS also lists 'Apache' (fills the heat gap between Loco and Prairie Fire), 'Hot Thai' (up to 200 fruits per plant, the highest stated yield of the six), and 'Prairie Fire' (max 30cm height, windowsill-viable, and the hottest by far), all AGM.

Also worth considering

Best Chilli Pepper Varieties for Scotland → compares all named chilli pepper varieties head-to-head, with the practical detail that doesn't fit in a summary card.

Care

Keep temperatures above 12°C, ideally above 15°C: fruiting is reduced above 30°C, so shade and ventilate on the hottest days. Raise humidity by damping down the greenhouse floor daily, which also helps deter red spider mite. Water little and often, keeping compost evenly moist; the deliberate dry-out described below is a different goal. Feed weekly with an organic high-potash liquid fertiliser once flowering starts. Support larger varieties with a cane, since the stems are brittle and snap easily under a heavy crop.

If maximum heat matters more to you than yield, there is a trade-off: letting plants dry out completely between waterings stresses them into producing more capsaicin, but this weakens the plant and reduces its overall harvest. Choose one goal or the other rather than expecting both.

Harvesting

Ready from mid-summer into autumn under cover. Pick green for a milder flavour, or leave fruit to ripen, usually to red, for more heat and sweetness; picking early keeps more fruit developing behind it. Cut with a knife or secateurs to leave a clean wound rather than tearing the plant. Chillies can be dried, frozen or pickled: store dried chillies in an airtight jar somewhere cool and dark.

Common problems

• Aphids target shoot tips and the undersides of leaves.
• Glasshouse whitefly feeds on sap and leaves sticky honeydew behind.
• Blossom end rot follows inconsistent watering, showing as dark blotches at the base of the fruit.

Common questions

Sources