Vegetable · Brassicaceae
When to plant watercress
A perennial of cold running water. In a garden it will grow in a bucket of wet soil stood in a tray, provided the water is changed rather than left to stagnate.
Hardy in USDA zones
5a to 11a
Winter cold sets the limit here, not the calendar.
Frost tolerance
Hardy
How much cold the plant itself will take.
Those weeks become real dates once you name a place.
Timing, in frost-relative terms
Nothing about a standing crop is sown to a calendar. Once planted, watercress stay in the ground for years, so the question is not when to sow but whether your winter is survivable and your planting window is open. Both answers come from your frost dates.
- Hardy in USDA zones 5a–11a.
Getting the timing right
Plant or sow in spring once the water has warmed, and pick from late spring onwards. Left alone it flowers in midsummer and the leaf turns bitter, so cut hard to keep it vegetative.
Frost tolerance
Hardy to about -6C. The crown survives cold happily as long as it does not freeze solid, which is what makes running water the traditional site.
Classified as hardy, with damage expected below -6°C (21.2°F)21.2°F (-6°C).