How to Grow Choy Sum (Sawi Hijau) at Home in Malaysia

Yes — choy sum (sawi hijau, 菜心) grows well in the Malaysian lowlands and is ready in roughly 30–40 days from sowing, which makes it one of the fastest brassicas you can grow. Grow it in rich, moist soil with plenty of sun and harvest as soon as the first yellow flowers open. The one key tip: protect it from flea beetles and caterpillars from day one — a fine insect net over the pot saves far more leaves than spraying later.

Quick facts

Item	Choy sum
Sun	Full sun to part sun, at least 4–6 hours; light afternoon shade helps on very hot balconies
Sowing	Seedling tray or direct sow, 0.5 cm deep
Germination	3–5 days
Spacing	10–15 cm between plants
Days to harvest	30–40 days from sowing, when the first flowers open
Container	At least 15–20 cm deep; troughs, polybags or styrofoam boxes

Choosing a spot and container

Choy sum likes bright light but appreciates a break from the harshest afternoon sun. On a condo balcony, an east-facing side with strong morning sun is ideal. If your balcony faces west, it still works — just water more carefully and consider a light shade net in the hottest months.

A long planter or styrofoam box at least 15–20 cm deep fits 6–10 plants comfortably. Single plants also do well in medium polybags. Every container needs drainage holes; brassicas sitting in waterlogged soil rot at the base.

Soil and potting mix

Choy sum grows fast, so it needs fertile soil that holds moisture but drains:

• 2 parts potting mix or loose garden soil
• 1 part compost
• A little burnt rice husk or cocopeat for drainage and air

If you reuse old potting mix, refresh it with compost first. Tired, compacted mix gives slow, tough plants that flower before they have grown properly.

How to sow choy sum step by step

Starting in a seedling tray lets you protect young plants and fill gaps easily, but direct sowing also works.

1. Fill a seedling tray with fine, moist seedling mix (or a 1:1 mix of cocopeat and compost).
2. Sow 1–2 seeds per cell, 0.5 cm deep, and cover lightly.
3. Water gently and keep the tray in bright shade. Seedlings usually appear in 3–5 days.
4. Move into more light as soon as seedlings emerge, or they will stretch and flop. Thin to one seedling per cell.
5. Transplant when seedlings have 3–4 true leaves, usually 2–3 weeks after sowing. Plant them 10–15 cm apart, at the same depth as in the tray.
6. Water in well and give a day or two of light shade so they settle.

For direct sowing, sow in rows 15 cm apart, 0.5 cm deep, a seed every 2–3 cm, then thin to 10–15 cm once seedlings have 2–3 leaves. Thinnings are edible.

Watering in hot and rainy weather

• Consistency is everything. Choy sum that dries out becomes bitter, fibrous and flowers too early. Water every morning; on hot, windy days check pots again in the late afternoon.
• Hot spells: a thin mulch of dry leaves, cocopeat or rice straw on the soil surface helps hold moisture.
• Rainy season: heavy rain and wet soil encourage soft rot at the stem base. Keep containers raised so they drain, avoid watering when the mix is already wet, and remove yellowing lower leaves that sit on the soil.
• Water at the soil, not over the leaves, in the morning.

Feeding

Choy sum is a leafy crop with a short life, so feed it early and regularly:

• Mix compost into the potting mix before sowing or transplanting.
• Start a liquid fertilizer about one week after transplanting (or when direct-sown seedlings have 3–4 leaves).
• Feed every 7 days at the label dilution until harvest.

Getting the dilution right matters — too strong can scorch roots in small pots. The calculator below converts the label rate into the amount for your watering can:

CalculatorsFertilizer Dilution CalculatorFertilizer dilution calculator: how many ml or grams of liquid or soluble fertilizer to mix for your watering can or sprayer, from ml/L or 1:N ratio.

Common problems and pests in Malaysia

• Flea beetles. Tiny black beetles that jump when disturbed and leave many small "shot holes" in leaves. They are worst on young plants. Cover pots with fine insect netting right after sowing or transplanting, and keep the soil surface clear of weeds and debris.
• Caterpillars (diamondback moth and others). Small green caterpillars that wriggle when touched and chew "windows" or holes in leaves, sometimes boring into the growing heart. Check leaf undersides every few days and hand-pick. Neem oil sprays in the evening help; products based on Bacillus thuringiensis (Bt) are a common organic option for caterpillars.
• Aphids. Clusters on young leaves and flower shoots. Spray off with water or use diluted neem oil or a mild soap solution.
• Snails and slugs. Feed at night, especially after rain. Hand-pick with a torch.
• Damping off and stem rot. Seedlings or young plants collapsing at the base. Use fresh mix, avoid overwatering and give good airflow.
• Early flowering with thin stems. Usually stress: crowding, drying out, poor soil or too little light. Space properly, feed and water regularly.

Choy sum, pak choy and other sawi share the same pests, so rotate where you grow them when you can. More natural methods:

GuidesOrganic Pest Control for Malaysian Home GardensIdentify aphids, whiteflies, mealybugs, thrips, spider mites, caterpillars, leaf miners, snails and fruit flies, and control them organically and safely.

Harvesting

Choy sum is harvested for its tender flowering stems, not only the leaves.

1. Watch for the first flowers. About 30–40 days after sowing, a central stalk with clusters of yellow buds forms. Harvest when the first one or two flowers open, while the stem is still thick and tender.
2. Cut the main stem about 15–20 cm long, leaving the lower leaves on the plant.
3. Second, smaller harvest. Side shoots often grow from the leaf joints left behind. Keep feeding and harvest these when they show their first flowers.

If you leave it too long, the stems become hollow and woody and the flowers open fully. Harvest in the cool of the morning and refrigerate quickly.

FAQ

What is the difference between choy sum and pak choy? Both are sawi from the same plant family. Choy sum is grown for its flowering stems and leaves; pak choy is grown for its leafy rosette with thick, spoon-shaped stalks. See the pak choy guide:

GuidesHow to Grow Pak Choy at Home in Malaysia (Soil or Hydroponic)Grow pak choy from seed in pots or a simple Kratky hydroponic setup. Sowing, spacing, watering, feeding, pests and harvesting for Malaysian balconies.

Why are my choy sum leaves full of tiny holes? Almost always flea beetles. Net the plants early and keep the area tidy; established plants usually outgrow light damage.

Can I save choy sum seed? It is possible, but plants take much longer to set seed, and choy sum cross-pollinates easily with pak choy and other sawi flowering nearby. For reliable results, buy fresh seed.

How often should I sow? Sow a small batch every 2 weeks for a steady supply.