Watercress
Nasturtium officinale · Perennial
A water-loving perennial with a peppery bite, and one of the few herbs that genuinely wants to sit in water. Refresh the water regularly to avoid algae.
What it needs indoors
- Light
- Bright lightBright, indirect to partial sun
- Water
- Standing waterConstant. Grow in standing water, refreshed regularly
- Temperature
- 50–70°F
- Growing medium
- Kept saturated; plastic container to reduce evaporation
- Native range
- Cold, flowing spring water in Europe and Asia
- Difficulty
- Beginner
What usually goes wrong
Water turns cloudy and starts to smell, stems go slimy at the base
Stagnation. Watercress grows in cold running spring water, and a still tray in a warm room goes anaerobic within days.
Fix: Change the water every day or two, twice a day in a warm room. Keep the tray shallow and in the coolest bright spot available, and pull out any soft stems before they take the rest with them.
Green film across the water and up the sides of the container
Algae, feeding on light and whatever is dissolved in standing water.
Fix: Swap the glass for an opaque container, keep direct sun off the water surface while still giving the leaves bright light, and refresh regularly. Scrub the container out at every change.
Flower stems rise and the leaves turn hot and stringy
Above about 70°F it turns towards flowering, and the peppery bite tips over into harsh.
Fix: Keep it cold. A chilly windowsill or an unheated room suits it. Pinch flower stems out as they show and start replacements from cuttings, which root in water inside a week.
