Trapa natans
Water chestnut
Common names: Water walnut, Jesuit's nut
At a glance
- Light
- Full sun
- Spacing
- 60 cm, rows 60 cm
- Lifespan
- Annual
- Sowing
- Apr–May
- Harvest
- Sep–Oct
- Hardiness
- Cold damage below 0 °C
- Water need
- High
- Origin
- Native to Germany
Photo: CC BY-SA 3.0 · Source
This description was machine-translated.
Description
The water chestnut (Trapa natans) is an annual floating-leaf plant that thrives in warm, still shallow waters. Its diamond-shaped, glossy leaves form dense rosettes on the water surface, beneath which spiny, starch-rich nuts mature. The nuts develop a mild, nutty flavor when roasted or cooked. Native to Germany, the species is now rare and protected; plants or seeds should only be obtained from garden retailers, never from the wild. The plant is well suited for a sunny mini‑pond or a large watertight container without drainage for home gardens.
Care instructions
Plant seedlings only after the water has been consistently warm, typically from mid‑May (week 20), as the plant cannot tolerate cold. The container or pond requires full sun, still to slightly moving water, and a water depth of about 30 to 60 cm above a nutrient‑rich substrate layer. Keep the water surface free of competing plants so the leaf rosettes can spread, and fertilize sparingly with mature compost in the root zone. Harvest begins in September when the mature nuts detach from the rosettes and sink to the bottom; scoop them regularly before they subside. Because the plant is annual and does not survive frost, the season ends naturally with the first cold snap; for the next year, collect mature nuts for seed or purchase new seedlings.
The care notes were machine-translated from German.
Garden year
SowingApr–May
HarvestSep–Oct
Germination
- Soil temperature
- from 10 °C, ideally 20 °C
- Days to sprout
- 21 to 60 days
- Light
- Sprouts in light or dark
- Sowing depth
- 2 cm
- How to start
- Start indoors, then plant out
Soil & site
Soil pH
Soil type
moist, nutrient-rich, humus-rich, loamy
The water chestnut grows free-floating on calm, nutrient-rich waters with a soft, muddy bed. It does not need a classic garden soil, but shallow, warm still water with a humus-rich sediment as a source of nutrients. It tolerates low-lime to slightly chalky water well; what matters above all is the abundance of nutrients in the sediment.
Feeding
Medium feeder
In a well-established pond with nutrient-rich mud, the water chestnut needs no additional feeding. If the water is very clear and low in nutrients, a little mature compost or pond soil on the bed of the water helps when you introduce the young plants. Do not feed during flowering, so the water does not turn.
Overwintering
The water chestnut itself dies off after the fruit ripens in autumn, but its spiny nuts overwinter on the bed of the water and germinate anew in spring. Simply let the ripe nuts sink in the pond; no frost protection is needed. In very shallow waters that freeze solid, you can overwinter a few nuts frost-free in a container with moist substrate.
Propagation
Methods
- From seed
Propagation is exclusively through the characteristic, horn-like nuts, which sink to the bottom in autumn. Collect ripe nuts or leave them in the pond; they germinate by themselves as soon as the water warms up in spring. For a deliberate fresh start in another body of water, simply lay the nuts flat on the water; they sink to the bottom on their own. Keep the water calm and warm until germination, and new rosettes then form quickly.
For your garden
Grow Water chestnut yourself
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