Growing chillies: from seed to harvest

Chillies can be grown successfully in a central European climate – in the garden, in a greenhouse or in a pot on the balcony. This guide takes you from sowing to harvest and seed saving. All figures come from university extension services and scientific studies, linked at the end.

Contents: Sowing · Seedlings · Planting out · Water and feeding · Flowering and fruit · Pests and diseases · Harvest and heat · Overwintering · Seeds · Safety

1. Sowing: February to March

US university extension services recommend sowing 6–10 weeks before planting out (Clemson and Wisconsin 6–8 weeks, Penn State and Utah State 8–10 weeks); the Royal Horticultural Society (RHS) says “late winter to mid-spring”. With planting out in the second half of May (see below), that means sowing from about late February to March in central Europe.

Seeds need warmth: the RHS recommends about 21 °C in a heated propagator, the University of Wisconsin even 27–32 °C on a heat mat. Classic University of California data show how temperature affects emergence:

Soil temperature	Days to emergence
15 °C	25
20 °C	12.5
25 °C	8.4
30 °C	7.6 (fastest)
35 °C	8.8
40 °C	no germination

Below 15 °C seeds hardly germinate. For C. chinense (e.g. habanero), a Turkish study found the best germination at 24–27 °C and none at 9–15 °C.

2. Raising seedlings

• Temperature after emergence: RHS 16–18 °C in a bright spot; University of Wisconsin 21–24 °C by day and 16–17 °C at night; University of New Hampshire 18–21 °C by day and 13–16 °C at night.
• Light: windowsills get little light in February and March; UNH recommends supplementary lighting for about 16 hours a day, with tubes about 15 cm above the plants.
• Pricking out: when the first true leaves appear (UNH) or at 2–3 cm tall (RHS), into individual cells or small pots; when roots show through the drainage holes, move them to pots about 13 cm across.
• Hardening off: before planting out, gradually accustom plants to outdoor conditions – sources say 10 days (Wisconsin, Penn State) to 2–3 weeks (RHS). Start with a few hours outside a day and bring plants in when cold nights threaten.

3. Planting out: after the last frosts

Peppers love warmth. The RHS advises planting out once night temperatures reliably stay above 12 °C (growth is better above 15 °C); Penn State gives soil warmer than 15.6 °C and says growth stalls below 10 °C.

A Czech study (Potopová et al., 2014) found that in the Elbe lowland the risk of a damaging spring frost when planting vegetables is 25% after 3 May and 10% after 15 May. Last spring frosts have been arriving earlier in recent decades, but not everywhere – and May 2026 showed that the traditional “Ice Saints” (12–14 May) are no guarantee: according to the Czech Hydrometeorological Institute, it was still freezing at 55 stations on 17 May. In lowlands, plant out in the second half of May at the earliest; later at higher altitudes.

• Spacing: 38–45 cm between plants, dwarf varieties 30 cm (RHS); Penn State recommends 46 cm with rows at least 61 cm apart.
• Pots: a final pot of at least 22 cm (RHS); for a large plant, around 19 litres (Oregon State).
• Greenhouse: ventilate and shade above 30 °C and damp down the floor for humidity in hot weather (RHS).

4. Water, feeding and mulch

• Water: 25–50 mm a week (Oregon State, Utah State, Penn State). Even watering matters most during fruit set and development (Clemson).
• Feeding: the RHS recommends a high-potassium liquid feed weekly from the start of flowering; US extension services emphasise nitrogen (e.g. calcium nitrate 3–4 weeks after planting) but warn against excess.
• Mulch: helps keep moisture even (Clemson); put organic mulch down only once the soil has warmed (Utah State).
• Blossom-end rot (a dark sunken patch at the tip) is not a disease but a calcium shortage in fast-growing fruit, usually caused by irregular watering. Even moisture, mulch and moderate nitrogen help (University of Florida, RHS).

5. Flowering and fruit set

Pepper flowers have both male and female parts and readily self-pollinate; insects cause some crossing (NMSU). Temperature strongly affects fruit set:

• Nights below 13 °C or days above 32 °C cause flower drop (Utah State).
• Fruit sets best with night temperatures of 16–24 °C (Penn State).
• Above 30 °C fruiting is reduced (RHS); an experiment showed that just 48 hours at 33 °C reduced pollen viability and fruit set.

A myth: a sweet pepper next to a hot one will not turn hot this year. A cross shows up only in the next generation – in plants grown from seed saved from such a fruit. Natural crossing in C. annuum is low; in one study 1.2% of seeds were hybrids.

6. Pests and diseases

• Aphids: besides sucking sap, they spread viruses such as potato virus Y (PVY), transmitting it during brief probing before they settle to feed (UC IPM).
• Red spider mite: pale mottling on leaves, worst in hot, dry greenhouses; biological control with the predatory mite Phytoseiulus persimilis (RHS).
• Whitefly: honeydew and sooty mould; biological control with the parasitic wasp Encarsia formosa; yellow sticky traps are mainly for monitoring (RHS).
• Thrips: silvery patches with black specks of excrement, can spread viruses; control with predatory bugs Orius or mites Amblyseius, blue sticky traps (RHS).
• Tobacco and tomato mosaic viruses (TMV, ToMV): spread by seed and handling, not by insects. No chemical control exists – use resistant varieties (genes L1–L4), clean hands and tools, and remove infected plants (UC IPM).
• Damping-off: fungal diseases (Pythium, Rhizoctonia and others); prevent with fresh compost, thin sowing, mains water, ventilation and clean trays (RHS).

7. Harvest and heat

Mature green fruit is ready 35–50 days after flowering (NMSU), fully coloured 35–45 days after flowering (Utah State); outdoors in a cool climate allow an extra 15–20 days (Oregon State). Red colour develops best at 18–24 °C and stops below 13 °C (Wisconsin). Regularly picking green fruit increases the total crop (RHS).

Can you influence the heat? Capsaicinoids increase as fruit ripens – in habanero they peak about 45–50 days after fruit set, then decline slightly. Water stress increased heat in most cultivars. But variety matters far more: in a 2012 study it explained 74% of the differences in pungency, the environment only 6%. If you want hotter chillies, choose a hotter variety rather than stressing the plant.

What to do with the harvest? Chillies can be dried, pickled or fermented into sauce – fermentation is also how Sakay sauces are made.

8. Overwintering

Peppers are actually perennials grown as annuals. There are two ways to overwinter them:

• Warm and bright (RHS): cut the plant back and keep it on a warm, bright windowsill or in a conservatory, watering sparingly.
• Dormant (Oregon State): at 4–13 °C, cut back, under a grow light – for example in a garage. No fruit will ripen over winter.

9. Saving your own seed

Take seed from fully ripe fruit; ripe seeds are ivory or yellowish. Dry them for 2–3 days in shade on a hard surface (NMSU, World Vegetable Center). To keep a variety pure, the World Vegetable Center recommends 20 m isolation, Californian master gardeners 30 m; bagging or netting the flowers is more reliable. Store dry and cool (below 10–15 °C) in an airtight container; seed stays viable for at least 3–5 years.

10. Safety

Capsaicin irritates the eyes, mucous membranes and skin. Most of it sits in the white membrane (placenta) around the seeds; the seeds only pick it up by contact. Wear rubber, latex or nitrile gloves when cutting hot chillies, don’t touch your face, and wash your hands afterwards. If capsaicin gets into your eye, rinse with lukewarm water for 15 minutes; on skin, vegetable oil or diluted vinegar can help. Difficulty breathing or chest pain needs medical help – contact your local poison centre or emergency services.

Sources

1. Royal Horticultural Society: Chilli peppers; Sweet peppers; red spider mite; whitefly; thrips; damping-off
2. Clemson HGIC: Pepper
3. University of Wisconsin A3687: Growing tomatoes, peppers and eggplants
4. Penn State Extension: Growing peppers; Can you make them hotter?; Preserving the heat
5. Utah State University: Peppers in the garden
6. UC ANR: Seed germination temperature and timing (after Harrington 1954); UC IPM: tobamoviruses, potyviruses
7. University of New Hampshire: Starting plants from seed
8. Oregon State University: Grow your own peppers; Overwintering
9. UF/IFAS: Blossom-end rot
10. NMSU: H-230; H-262 Saving chile seed
11. World Vegetable Center (AVRDC, 2006): Saving your own pepper seed
12. Potopová V. et al. (2014). Natural Hazards 71: 1–19. doi:10.1007/s11069-013-0894-5
13. Zahradníček P. et al. (2024). Theoretical and Applied Climatology 155: 965–984. doi:10.1007/s00704-023-04671-2
14. Czech Hydrometeorological Institute (11 Jun 2026): Minimální teploty v květnu 2026
15. Gökpınar, Balkaya, Şahin (2021). doi:10.21597/jist.1027991
16. Erickson A. N., Markhart A. H. (2002). Plant, Cell & Environment 25: 123–130. doi:10.1046/j.0016-8025.2001.00807.x
17. Justino et al. (2018). Genetics and Molecular Research 17(1). doi:10.4238/gmr16039887
18. Contreras-Padilla M., Yahia E. M. (1998). J. Agric. Food Chem. 46: 2075–2079. doi:10.1021/jf970972z
19. Phimchan P. et al. (2012). HortScience 47: 1204–1209. doi:10.21273/HORTSCI.47.9.1204
20. Gurung T. et al. (2012). Euphytica 187: 11–18. doi:10.1007/s10681-012-0672-6
21. National Capital Poison Center: Capsaicin: when the chili is too hot
22. VFN Praha: press release on the Czech Toxicological Information Centre