Gadenin日本語Get the appCheck the law before you sow a single seed
Water spinach, also sold as kangkong or ong choy, is listed as a federal noxious weed in the United States. Growing, moving or selling it is restricted, and several states run their own permit systems on top of the federal listing. Other warm regions, including parts of Australia and the Pacific, treat it the same way. Before you sow, confirm what applies where you live; a permit is often obtainable for enclosed home growing, but you need it first.
The reason is simple and worth taking seriously. A single cut stem that lands in a ditch, pond or canal can root and grow into a floating mat that shades out everything under it. Whatever the rules say, keep every plant, every trimming and every drop of tray water away from any waterway or storm drain. Spent plants go in the bin or a hot compost pile that you turn, never on an open pile near water.
The practical consequence for sowing is that you should site the crop where runoff is controlled: a raised bed, a container, or a tray on a hard surface. That happens to suit the plant anyway, because it likes standing water more than any other leafy green you will grow.
Nothing in this guide is legal advice. Rules change, and they differ between countries, states and counties. Confirm your own position with your agriculture department before planting.
It will not move until the soil is genuinely warm
This is a tropical plant and it behaves like one. Seed sown into cool ground sits and rots. Wait until soil at two inches (5 cm) is holding above 70F (21C) day and night, which in most temperate gardens means well after the last frost, when you would be sowing okra or planting out peppers. At 75 to 85F (24 to 29C) germination is fast and even.
Air temperature matters as much as soil. Below about 60F (15C) growth stops and the leaves go a dull yellow-green even on established plants. If your season is short, start seed indoors in cell trays three weeks before the ground is ready and plant out into warm soil, or grow the whole crop in a container you can move against a sunny wall.
Seed has a hard coat. Soak it in water at room temperature for twelve to twenty-four hours before sowing and you will see the seeds swell to nearly double. Discard any that still float hard and dry after a full day; they are usually blind. Soaked seed comes up in three to seven days in warm soil, unsoaked seed can take two weeks or never.
| Condition | Target | What happens outside it |
|---|---|---|
| Soil temperature | 70 to 85F (21 to 29C) | Below 65F (18C) seed rots instead of sprouting |
| Sowing depth | Half an inch (1 cm) | Deeper than an inch and emergence goes patchy |
| Soak before sowing | 12 to 24 hours | Dry seed germinates late and unevenly |
| Moisture | Soil never dries at the surface | One dry afternoon kills a whole flat of seedlings |
| Days to emergence | 3 to 7 days | Longer than 10 days means the soil is too cool |
Sow thickly and grow it as a cutting bed
You are not growing individual specimen plants. Water spinach is cut and re-cut like a cut-and-come-again green, so a dense stand gives you more tender stem per square foot than widely spaced plants do. Sow in rows six to eight inches (15 to 20 cm) apart, dropping seed every one to two inches (3 to 5 cm) along the row, and thin only enough to stop the stand collapsing into a tangle.
Aim to end up with plants about four inches (10 cm) apart in the row for the upland style of growing in beds, or closer if you are cutting young. Thinnings are edible, so pull them at the four-leaf stage and use them raw. Do not transplant thinnings back into gaps unless you can keep them wet for a week; the roots resent disturbance in dry air.
If you want a tray culture instead, fill a wide plastic tub with four inches (10 cm) of soil, sow across the whole surface, and once the seedlings have three true leaves top the tub up so the water sits about half an inch (1 cm) above the soil. Grown that way the plant makes hollow, crisp stems and you almost never have to think about watering again.
- Soak the seed Cover the seed with room-temperature water in a jar and leave it twelve to twenty-four hours. Drain it and sow the same day. Soaked seed left sitting damp for a second day starts to sour and loses viability quickly.
- Prepare wet, rich ground Water spinach is a heavy feeder. Work two to three inches (5 to 8 cm) of compost into the top six inches (15 cm) of the bed, level it, and flood it the day before sowing so the whole profile is saturated rather than damp on top only.
- Sow and cover lightly Drop seed every one to two inches (3 to 5 cm) in rows six to eight inches (15 to 20 cm) apart, cover with half an inch (1 cm) of soil, and firm gently. Water with a fine rose so you do not wash the seed into drifts.
- Keep it wet until it is up Never let the surface dry in the first week. In hot weather that can mean watering twice a day, or laying a piece of shade cloth over the bed until the first seedlings show and then taking it straight off.
- Thin to four inches (10 cm) At the four-leaf stage, pull surplus seedlings so the survivors stand about four inches (10 cm) apart in the row. Eat the thinnings. Bin any waste rather than tossing it where it could wash into a drain or ditch.
Write down the sowing date and the soil temperature
Record the date you sowed, the soil temperature you measured that morning, whether you soaked the seed, and the date the first true leaf appeared. After one season you will know exactly how early your particular garden can take this crop, which is the single most useful number to own, because sowing water spinach two weeks too early costs you the whole flat.
Also note where the bed or tray sat and how much sun it got. Water spinach responds so strongly to heat that the same seed in two positions in one garden can differ by two weeks to first cut, and next year you will want the better spot.