Grow Thai chillies in pots: from seed, pot size, flowering, and why flowers drop

Thai bird’s eye chillies grow well in pots if they get three things: at least 6 hours of sun, a big enough pot, and steady water. Germinate the seed somewhere warm, about 25-28°C, and it comes up in around 8 days. Move the seedlings into pots at 4-5 weeks, and roughly 70-85 days later you start picking ripe chillies. This lesson goes step by step and ends with the question chilli growers ask most: why are the flowers dropping?

Chillies grown in Thailand

Thai chillies fall broadly into bird’s eye types, the longer Bang Chang types, and the mild Yuak types. An FAO report notes that most Thai chillies have no standard cultivars; growers save their own seed. A packet of seed or seed from a fully ripe fruit both work. Hot chillies cope with heat better than sweet peppers, but they still have limits, as the section on flower drop shows.

Germination: temperature is everything

Figures from the World Vegetable Center’s chilli guide, developed in the Taiwan lowlands:

Soil temperature	Time to germinate
25-28 °C	About 8 days
20 °C	About 13 days
15 °C	About 25 days
Below 15 °C or above 35 °C	May not germinate at all

Use a clean, free-draining seed mix, sow one seed per cell about 1 cm deep, and water every morning with a fine rose: not too wet, not too dry. Setting the tray under insect netting gives some shade and shields it from heavy rain and from aphids, which carry viruses.

In the hot season, a tray in full sun can heat past 35°C. Keep it in bright shade until the seedlings are up.

Moving seedlings into pots

Seedlings are ready at 4-5 weeks after sowing, with 4-5 true leaves, stocky, disease-free and not yet flowering. If they grew in shade, harden them off over 4-5 days: 3-4 hours of direct sun on day one, more each day, full sun by day four.

Transplant in the late afternoon or on a cloudy day, set the plant as deep as its seed leaves or first true leaves, and water straight away.

Pot size. Sources differ. University of Maryland Extension recommends at least 5 gallons (about 19 litres) per pepper plant. Its container guidance puts large vegetables such as peppers at 8-10 gallons (about 30-38 litres) of mix, 30-40 cm deep, and dwarf peppers at 4-6 gallons (about 15-23 litres). The simple rule: one chilli plant per pot, no less than about 19 litres, and bigger if you have the room. The pot needs drainage holes; dark colours can heat the soil enough to harm young roots, and a layer of gravel in the bottom does not improve drainage.

Chilli roots are shallow and tolerate neither drought nor waterlogging well. Plants left standing in water for more than 48 hours usually wilt and die. A pot sitting in a full saucer during the rainy season is the most common trap.

Care until flowering

• Sun: at least 6 hours a day, 8-10 is better.
• Water: aim for evenly moist soil. Dry soil causes flower drop, small fruit and blossom end rot. Water at the base and do not soak the leaves in the evening; leaves that stay wet overnight invite disease.
• Mulch: straw or dry grass keeps moisture in and the roots cooler.
• Stake: give each plant a stake before it flowers. Chilli branches are brittle and snap under a heavy crop.
• Remove the first flowers: the guide recommends removing flowers and fruit that set at the first fork, along with leaves and shoots below that fork. The plant grows stronger and foliar disease spreads less.
• Feed: compost at planting and again after the first fruit sets. See Make compost from kitchen scraps.

Worked example: counting from seed to ripe chilli

Using the guide’s figures - 4-5 weeks for seedlings, and most hot peppers ripening about 70-85 days after transplanting - say you sow on 1 November.

1. Seedlings for 5 weeks = 35 days, so you transplant around 6 December.
2. Count 70 days on: 25 days left in December, 31 in January makes 56, plus 14 in February - about 14 February.
3. Count 85 days: 15 more days; February has 28 days, so about 1 March.
4. The first ripe chillies arrive between mid-February and early March.

The advantage of starting then is that the plants flower in the cool season, when nights are cooler, so flowers set fruit more easily than during a run of warm nights.

Why flowers and small fruit drop

When nearly all the flowers or tiny fruit fall, the cause is usually one of the weather or care problems below. Work down the list.

Cause	What to look for	What to do
Nights too warm	Night temperature above about 24 °C for several nights	Wait for cooler weather; healthy plants start setting again
Very hot days	Days above about 32-35 °C for long spells	Give late-afternoon shade; mist the leaves in hot, dry spells
Nights too cool	Nights below about 15 °C	Rare in the Thai lowlands; wait for warmer weather
Soil long dry or soggy	Bone-dry soil, or a pot standing in water	Water evenly; fix drainage
Too much shade	Less than 6 hours of sun	Move the pot somewhere sunnier
Too much nitrogen	Dark leaves, lots of shoots, few flowers	Stop the leafy fertiliser
Hot, dry wind	Leaves and flowers wilt in the afternoon	Add a windbreak, mulch
Fruit not picked	Lots of ripe fruit left on the plant	Pick regularly

The temperatures come from two sources. The World Vegetable Center says chilli sets fruit poorly when nights exceed 24°C, and growth drops when temperatures stay above 32°C for long periods. University of Maryland Extension says nights below 60°F (about 15.5°C) or above 75°F (about 24°C), or days above 95°F (35°C), can make flowers and small fruit drop, and that healthy plants resume fruiting once it cools.

Diseases that come with rain

Anthracnose shows as water-soaked, sunken spots on mature fruit that spread fast. It appears wherever fruit gets wet from rain or overhead watering, and it can be carried on seed and in plant debris. Reduce it by using seed from disease-free fruit, picking often (or picking green), and removing spotted fruit.

Do not plant chillies in soil that just grew tomatoes or eggplant; these related crops share many soil-borne diseases. In pots, use fresh soil.

Common mistakes

• A pot that is too small. Stunted plants, soil that dries fast, flowers that drop.
• Saucers full of water in the rainy season. Roots drown and the plant collapses.
• Pushing nitrogen. You get leaves, not chillies.
• Transplanting seedlings that are already flowering. Overgrown seedlings often stall for a long time.
• Cutting chillies or removing seeds bare-handed. Wear gloves and keep your hands away from your eyes.

The next lesson keeps leafy greens such as Chinese kale, choy sum and lettuce going in Thai heat, and lesson eight covers tomatoes, which drop their flowers in the heat much as chillies do.

Sources

• Suggested Cultural Practices for Chili Pepper — World Vegetable Center
• Growing Peppers in a Home Garden — University of Maryland Extension
• Poor Blossom and Fruit Set of Vegetables — University of Maryland Extension
• Types of Containers for Growing Vegetables — University of Maryland Extension
• The vegetable sector in Thailand: Chilli — FAO