Grow water spinach (pak bung) in pots: harvest in 3-4 weeks, cut and regrow

Upland water spinach (pak bung jeen in Thai, also sold as kangkong) is one of the fastest vegetables you can grow. Sow the seed in a pot or bed in full sun, keep the soil moist every day, and in roughly 20-30 days you can pull whole plants. If you want a longer supply, cut the stems above the soil and let the stumps send up new shoots. This lesson covers sowing, timing, and how to cut so the same plants keep producing.

If you have not set up a growing spot and soil yet, read Start a pesticide-free garden in a small space first.

Pak bung jeen is the upland type

Water spinach comes in two main forms: an aquatic type that grows in water, and an upland type grown on moist soil. The pak bung jeen seed sold in Thailand is the upland type. In Thailand, Malaysia and Singapore it is broadcast or sown in rows on raised beds and pulled whole at about 20-30 days.

	Pak bung jeen (upland)	Aquatic type
Propagation	Seed	Cuttings pushed into mud or water
Where	Beds or pots, moist but not waterlogged	Paddies, ponds, ditches
First harvest	About 20-30 days after sowing (some cultivars longer)	About 1-2 months after planting
How you harvest	Pull whole, or cut and let it reshoot	Repeated cutting of shoots
For a home garden	Easy, easy to control	Needs a container that holds water

Days to harvest vary with cultivar and weather. The Southeast Asian vegetable handbook gives a wide 20-50 days, and an FAO record notes one Thai upland cultivar taking about 55 days to first harvest. Go by the days printed on your seed packet.

Sun, temperature and water

Water spinach does best in the lowland tropics with full sun and steady heat. Seed germinates poorly below 25°C, and growth becomes too slow once the average temperature drops below about 23-25°C. Thailand’s hot and rainy seasons are when it races; in the cool season it still grows, just more slowly.

Water is the big one. The upland type needs high soil moisture, so water every day and water thoroughly. Young plants cannot handle standing water, though, so pots need drainage holes and no saucer left full of water.

One more thing: water spinach is a short-day plant. Days with less than 12 hours of daylight, as at the end of the year in Thailand, trigger early flowering, and dry soil does the same. Once it flowers, the shoots toughen and fewer new ones appear. In that season, lean towards pulling whole plants early rather than keeping stumps going for a long time.

Container and soil

The roots are shallow, so a trough or shallow pot works. University of Maryland Extension’s container guidance puts small leafy crops such as Asian greens at a minimum of about 4-11 litres (1-3 gallons) of mix, 10-15 cm deep. A long trough at least 15 cm deep is enough.

It likes soil rich in organic matter with a pH of about 5.3-6.0, slightly acidic. Loam mixed with fine compost works well, and you can make the compost from kitchen scraps - see Make compost from kitchen scraps.

Go easy on nitrogen. The handbook notes that too much nitrogen raises the nitrate content of the leaves and gives you more stem than leaf. Moderate compost beats pushing growth with chemical fertiliser.

Worked example: one 60 x 20 cm trough

From the handbook: upland beds carry 30-170 plants per square metre, and ordinary seed often germinates below 60% when it is old and hard-coated, while improved seed from a reliable source usually tops 80%. Let’s work it out.

1. Trough area: 0.6 x 0.2 = 0.12 m².
2. Aim for a middle density of about 100 plants per m²: 0.12 x 100 = 12 plants.
3. Assume 70% germination: 12 / 0.7 ≈ 17 seeds. Round up to 18-20.
4. Sow two rows about 10 cm apart, 9-10 seeds per row, cover thinly with soil, and water.
5. If they come up too thick, pull the crowded ones and eat them as baby greens.

For water spinach every week, use two or three troughs and sow them 7-10 days apart. By the time you have cleared the first, the next one is ready.

Pull, or cut and let it reshoot

Pull the whole plant. Simple, and you get the whole tender plant. This is how most commercial upland beds in Thailand are harvested. Afterwards, rest the soil, add compost, and sow again.

Cut and let it reshoot. The handbook notes that repeated cutting of upland water spinach is mainly a home-garden practice. Cut the stems above the soil and leave a stump with nodes on it; the buds at those nodes grow into new shoots. For the aquatic crop, the handbook gives cutting 5-10 cm above the ground every 4-6 weeks, and the same height works in a pot.

To judge timing: side branches start to form about 2-3 weeks after sowing, and each shoot puts out a new leaf roughly every 2-3 days. New shoots from a stump therefore reach picking length within a few weeks, depending on sun and water.

After every cut, scatter a thin layer of compost around the stumps and water it in. The handbook recommends extra feeding after each cutting, because the plant has to rebuild its shoots from scratch.

Pests and diseases you’ll meet

• Leaf-eating caterpillars such as the common cutworm love the tender tips, especially on stumps you keep cutting. Walk the bed each morning and pick off caterpillars and egg clusters by hand.
• Aphids cluster on tips and leaf undersides. Knock them off with a strong spray of water, or pinch off badly infested tips.
• White rust is the most common disease of water spinach: white pustules under the leaves. Remove affected leaves and do not crowd plants so tightly that air cannot move.
• Damping-off makes seedlings collapse at the base, usually in soggy soil. Keep drainage good.
• Root-knot nematodes trouble stumps kept for a long time on dry land. If the roots are lumpy and knotted, pull the plants and change the soil.

Common mistakes

• Watering every other day. Water spinach needs moist soil daily; dry soil makes stems stringy and pushes it into flower.
• Cutting so low that no nodes remain. No buds, no regrowth.
• Growing it in shade. You get thin, stretched stems and few leaves; it needs strong sun.
• Heavy nitrogen. Lush plants, but more nitrate and fewer leaves.
• Keeping stumps going after flowering. New shoots come up small and tough; resow instead.

Wash it well before eating even when you grew it yourself - see Washing vegetables properly. The next lesson grows chillies in pots, another crop no Thai kitchen can do without.

Sources

• Ipomoea aquatica (PROSEA) — Pl@ntUse
• Ipomoea aquatica (PROTA) — Pl@ntUse
• The vegetable sector in Thailand: Kangkong — FAO
• Types of Containers for Growing Vegetables — University of Maryland Extension