How to Grow Thai Chili Peppers

Thai chili peppers are among the easiest hot peppers to grow: compact, bushy plants about 1 to 2 feet tall that cover themselves in small, upright pods ripening from green to bright red. Start seeds indoors 8 to 10 weeks before your last frost at a warm 80 to 85°F soil temperature, transplant outside once nights stay above 55°F, give them full sun and steady moisture, and pick often to keep the plant setting new fruit. Because a Thai pepper plant is a perennial in frost-free climates, you can also bring it indoors in fall and keep it producing for years. Here is the full process, outdoors and indoors.

Part of our Vegetable Gardening & Raised Beds guide →

In this guide

1. About the Thai Chili Pepper Plant
2. Choosing a Variety
3. Starting Thai Peppers From Seed
4. Hardening Off and Transplanting
5. Watering and Feeding
6. Keeping Thai Pepper Plants Producing
7. Growing Thai Chili Peppers Indoors
8. Overwintering a Thai Pepper Plant
9. Harvesting and Using Thai Chilies
10. Common Problems
11. Frequently Asked Questions

About the Thai Chili Pepper Plant

“Thai chili” covers several small, very hot peppers used in Southeast Asian cooking, often sold as Thai Hot, Thai Dragon or bird’s eye chilies. Most seed varieties sold in the US are Capsicum annuum, with some bird’s eye types classed as C. frutescens. The pods are typically 1 to 2 inches long, thin-walled and pointed, and commonly rated somewhere around 50,000 to 100,000 Scoville heat units, depending on variety and growing conditions. That is several times hotter than a jalapeño but well below habanero heat.

The plants themselves are ornamental: dense, small-leaved bushes with fruit held upright above the foliage, often in red, orange and green all at once. They mature in roughly 80 to 100 days from transplanting, so most of the US has enough season for a good crop, and the compact size makes them one of the best hot peppers for patios and windowsills. For the general principles that apply to all peppers, see our guide on how to grow peppers.

Choosing a Variety

Seed catalogs list several Thai-type peppers, and the names overlap. The differences are mostly plant size, pod shape and how the fruit is held.

• Thai Hot: the classic compact plant, often under about 18 inches, with masses of tiny upright pods. A good choice for containers and windowsills.
• Thai Dragon: a taller, more productive type with slightly longer pods, better suited to garden beds where it has room to spread.
• Bird’s eye types: very small, often rounder or bullet-shaped pods with intense heat; some are slower to germinate and mature, especially C. frutescens selections.
• Ornamental Thai-style peppers: bred for colorful, upright fruit on tidy plants. They are edible, but flavor and heat vary, so read the description if you plan to cook with them.

Whichever you choose, buy fresh seed from a reputable supplier and note the days to maturity listed on the packet. In short-season northern gardens, pick the earliest variety available and start seeds on the early side of the recommended window. In long, hot southern summers, nearly any Thai type will produce until frost, with a pause during the hottest weeks.

Starting Thai Peppers From Seed

Few nurseries carry Thai pepper transplants, so most gardeners start from seed. Hot pepper seed germinates slowly and needs warmth, which is where most first attempts go wrong.

1. Timing: sow 8 to 10 weeks before your average last frost date. In much of zone 6, that means late February to early March.
2. Sowing: plant seeds about a quarter inch deep in a moist seed-starting mix, two seeds per cell.
3. Heat: set trays on a seedling heat mat to hold the soil at 80 to 85°F. At typical room temperatures in the 60s, germination is slow and patchy.
4. Patience: most seeds sprout in 7 to 21 days. Keep the mix moist but not soggy, under a humidity dome until sprouts appear.
5. Light: as soon as seedlings emerge, remove the dome and put them under a grow light 2 to 4 inches above the tops for 14 to 16 hours a day. A windowsill alone usually produces leggy seedlings.
6. Thinning and potting up: snip the weaker seedling in each cell. When the first true leaves appear, move seedlings to 3- or 4-inch pots.

Our seed starting guide covers lights, mixes and timing in more detail.

Hardening Off and Transplanting

Peppers hate cold. Wait until at least two weeks after the last frost, when nights stay above 55°F and the soil has warmed to about 65°F. Planting into cold soil stalls peppers for weeks; they rarely make up the lost time.

• Harden off over 7 to 10 days, starting with an hour or two of shade outside and increasing sun and time daily.
• Site: full sun, 6 to 8 hours or more, in well-drained soil rich in organic matter with a pH of about 6.0 to 7.0.
• Spacing: 12 to 18 inches between plants, rows 18 to 24 inches apart. Thai peppers stay compact, so they fit tighter than bell peppers.
• Planting: set plants at the same depth or slightly deeper than in their pots, water in well, and mulch once the soil is warm.

In cooler regions, black plastic mulch or a planting spot against a south-facing wall adds warmth. In containers, a 3- to 5-gallon pot per plant is plenty; our guide to growing chili peppers in pots covers potting mix, pot size and container watering, so we will not repeat it here.

Watering and Feeding

Water deeply when the top inch of soil is dry, roughly 1 to 2 inches a week in the ground depending on heat and rain. Consistent moisture prevents flower drop and blossom-end problems; letting plants wilt hard and then flooding them stresses them. Some growers believe slightly drier conditions near harvest make hotter peppers, but severe drought mostly reduces the crop.

Mix a balanced, slow-release vegetable fertilizer or compost into the soil at planting. Once the plants begin to flower, switch to a fertilizer lower in nitrogen and higher in phosphorus and potassium, applied every 2 to 3 weeks at label rate. Too much nitrogen gives a big leafy bush with few peppers.

Keeping Thai Pepper Plants Producing

• Pick often. Harvesting ripe peppers signals the plant to set more fruit. Leaving every pepper to dry on the plant slows new flowering.
• Pinch early flowers. Removing the first few flowers in the two weeks after transplanting lets the plant build a stronger frame before it starts fruiting.
• Watch the heat. Flowers often drop when days are above about 90°F or nights stay above about 75°F. Production resumes when temperatures moderate. See why pepper flowers drop for other causes.
• Support heavy plants. A short stake keeps a laden plant upright in wind.
• Help pollination indoors. Peppers self-pollinate, but indoor plants benefit from a gentle shake or a small fan to move pollen.

Growing Thai Chili Peppers Indoors

The compact habit of Thai peppers makes them one of the best hot peppers to grow inside year-round. Give them a south-facing window plus a grow light, or a grow light alone running 14 to 16 hours a day. Keep the room between 65 and 80°F, water when the top inch dries, and feed at half strength every few weeks. Expect smaller harvests than outdoor plants, but a steady trickle of peppers even in winter is realistic under good lights.

Overwintering a Thai Pepper Plant

Thai pepper plants are perennial in zones 10 and 11 and can live several years if protected from frost elsewhere. A second-year plant starts fruiting much earlier in the season than a seedling.

1. Before the first fall frost, when nights fall into the 50s, pick all the peppers.
2. Dig the plant (or bring in its pot) and prune it back to a Y-shaped main stem about 6 to 10 inches tall, removing most leaves.
3. Rinse the roots and foliage to remove hitchhiking insects, and repot in fresh mix.
4. Keep it in a cool, bright spot around 55 to 65°F and water sparingly, just enough to keep the stems from shriveling. The plant will rest.
5. About 6 to 8 weeks before your last frost, move it to warmth and bright light, resume normal watering and feeding, and harden it off for planting out.

Alternatively, keep the plant growing actively indoors under lights all winter as described above.

Harvesting and Using Thai Chilies

Thai peppers can be eaten green, but they are hottest and most flavorful when fully red. Cut the stems with scissors or pruners rather than pulling, which can break branches. Wear gloves when handling a big harvest, and never touch your eyes afterward; capsaicin oils linger on skin.

• Fresh: refrigerate unwashed in a paper bag for one to two weeks.
• Frozen: freeze whole in a bag; they slice easily straight from the freezer.
• Dried: thin walls make Thai chilies easy to air-dry on a string in a warm, dry, airy room over a few weeks, or in a dehydrator. Grind dried pods into flakes.
• Preserved: use in chili oil, hot sauce, or fish sauce-based dipping sauces.

Common Problems

• Aphids and spider mites: especially indoors. Spray off with water or use insecticidal soap; check leaf undersides weekly.
• Yellowing leaves: often overwatering, cold soil or nitrogen shortage. See our guide on yellow pepper leaves.
• Leggy seedlings: not enough light; lower the grow light.
• Few peppers on a big plant: too much nitrogen, too little sun, or extreme heat.

For more vegetable growing guides, visit our vegetable gardening hub.