Growing chillies indoors in the UK
Updated: 21 October 2026
You have a windowsill, a greenhouse, or both, and you need to know which of these packets can live there. Growing chillies indoors in the UK works when the plant is compact, the glass faces south, and you do not move anything outside while nights are still under 12°C. A tall packet will not become a sill plant because the room is warm. The twelve listings are in the [Chili seeds comparison](/hub/herb-seeds/chili-seeds). Peter F. used the RHS, Which?, and Sea Spring’s windowsill notes, plus the habit words on these packets. He did not measure a plant. A qualifying purchase can earn a commission at no extra cost to you.
You have a windowsill, a greenhouse, or both, and you need to know which of these packets can live there.
You have a windowsill, a greenhouse, or both, and you need to know which of these packets can live there. Growing chillies indoors in the UK works when the plant is compact, the glass faces south, and you do not move anything outside while nights are still under 12°C. A tall packet will not become a sill plant because the room is warm. The twelve listings are in the Chili seeds comparison. Peter F. used the RHS, Which?, and Sea Spring’s windowsill notes, plus the habit words on these packets. He did not measure a plant. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Plant habit | Listed Scoville | Seeds in packet | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  PRIMERASEMILLAS.COM Piri Piri | Very tall, slender | Over 100,000 | 10 | 7.4 | about £3.45 | View offer |
| Alternative |  PRIMERASEMILLAS.COM Bolivian Rainbow | Compact dwarf | 30,000–50,000 | 10 | 6.4 | about £3.45 | View offer |
| Alternative |  PRIMERASEMILLAS.COM Basket of Fire | Compact dwarf | About 80,000 | 10 | 2.7 | about £3.95 | View offer |
On this page
Windowsill, greenhouse, or outdoors
The RHS says the best crop is under glass: a greenhouse, polytunnel, or sunny conservatory. A windowsill is for a compact plant only. Outdoors waits until nights are reliably at least 12°C, usually late May or early June, after hardening off. Frost kills an early move, which Which? also says. About 20–30 cm is the RHS general height for a compact windowsill variety, inside a wider span of about 20–60 cm or more. Neither figure measures Bolivian Rainbow or Basket of Fire. An unheated greenhouse in early May can still fall below 12°C at night.
What these packets say about size
Bolivian Rainbow, £3.45 for 10 seeds, is described as a compact dwarf bush, 30,000–50,000, fruit from purple to red, 4.0 from 7 reviews. One written review says it did not grow. Basket of Fire, £3.95, uses the same dwarf wording and about 80,000, with no stars stored. It does not say F1, so a 0.1–0.5 m band from other pages stays off it. Thai Dragon, Piri Piri, and Tabasco are the tall listings. Piri Piri is 4.5 from 16 and the title also names Tabasco. The Scorpions, Reapers, Scotch Bonnet Red, and Jamaican Red are medium bushes, with no centimetres. The jalapeño habit is blank. Which? saw a different Scotch Bonnet Red, not ASIN B0FH6Q855X, lose its shape in a 5 litre pot. Do not copy that litre onto this packet.
Light, water, and fruit set indoors
Sea Spring’s workable window faces south. East or west is a struggle, and north wastes the season. Several listings ask for six hours of direct sun, which a February back room will not give. Water a sill pot less than a greenhouse pot, and do not leave it standing in water. Above 30°C, ventilate, because the RHS says fruiting can drop. Shake flowers in still air, especially on Capsicum chinense. One jalapeño review from a flat reported two small harvests and blamed pollination. Shaking does not turn a north window into a south one, or fit a tall Tabasco in the frame.
The outdoor temperature line
Chillies cope at about 12°C at night and grow better above 15°C, on the RHS account. Move them out only after two to three weeks of hardening off, when nights stay at 12°C, usually late May or early June. H2 means the Reaper does not survive freezing. Several sellers print outdoors only above 15°C. Piri Piri and Tabasco print above 12°C. Follow the RHS line. Kew still has frost into late May or June. If the greenhouse cannot hold 12°C overnight, keep the plants indoors. No height in this article measures these twelve packets.
Common questions
Can I grow chilli seeds on a windowsill in the UK?
Yes, if the window is bright, ideally south-facing, and the variety is compact. In this set that wording is Bolivian Rainbow and Basket of Fire, and neither listing gives a height in centimetres. A north window is a poor place for the season. You still germinate them warm, at about the RHS 21°C, which is a sowing step rather than a property of the sill.
Which packets in this set are described as compact?
Bolivian Rainbow and Basket of Fire are described as small compact dwarf bushes. Thai Dragon, Piri Piri, and Tabasco are described as tall. The Scorpions, Reapers, Scotch Bonnet Red, and Jamaican Red are medium bushes, with no centimetre height stored. The jalapeño listing does not state a habit.
Is a greenhouse better than a windowsill?
The RHS says the best crop is under glass: a greenhouse, polytunnel, or sunny conservatory. A sill is for a compact plant when that is the space you have. An unheated greenhouse can still be too cold at night in May, so glass is better only when you can hold nights around 12°C or keep the plants indoors until you can.
How much light does a sill plant need?
Sea Spring treats a south-facing window as the workable one, east or west as a struggle, and north as a waste. Several of these listings ask for at least six hours of direct sun. A February sill will not match a July one. Give the seedlings the brightest glass you have, and do not expect a back room to finish the fruit.
When can the pot go outside?
When nights are reliably at least 12°C, usually late May or early June, after two to three weeks of hardening off. They grow better above 15°C. Do not use a single warm afternoon, and do not ignore frost that can last into late May or June. Seller lines of 12°C or 15°C do not replace that RHS rule.
What night temperature should a greenhouse hold?
About 12°C is the RHS coping temperature at night, with better growth above 15°C. Above 30°C, ventilate, because fruiting can drop. If the house cannot stay at 12°C overnight, leave the plants in a warm room. The plant is frost-tender. H2 does not mean hardy outdoors.
Will a tall chilli fit indoors?
Not on a small sill. Piri Piri and Tabasco are described as very tall and slender, and Thai Dragon as a tall bush. A greenhouse can take a larger plant if you have the height and the night temperature. Still air may not set fruit, so shake the flowers, especially on a chinense type. No centimetre height is printed for those three packets, so tall is the listing's word, not a measured clearance.
Related pages
Sources
Public UK sources named below. amazon.co.uk prices, stars and review counts on these twelve listings were read on 19 October 2026. Page updated 21 October 2026.
- RHS: grow your own chilli pepper (retrieved 19 October 2026)
- RHS: Capsicum chinense Carolina Reaper (retrieved 19 October 2026)
- Kew: chillies (retrieved 19 October 2026)
- Which?: how to grow chillies (retrieved 19 October 2026)
- GOV.UK: plants that need a plant passport in Great Britain (retrieved 19 October 2026)
- GOV.UK: issuing plant passports in Great Britain (retrieved 19 October 2026)
- The Seed Marketing Regulations 2011, Schedule 3 (retrieved 19 October 2026)
- Guinness World Records archive: hottest chilli, 2017 (retrieved 19 October 2026)