Watercress Through the Year: What to Do in Each Season

The shape of the watercress year

Watercress is a perennial of cool running water, and its year is defined by temperature rather than by day length or frost. It grows fast and tastes mild between 50 and 68F (10 to 20C), which means spring and autumn are its two proper seasons. Above about 77F (25C) it slows, the leaves turn fiercely peppery, and the plant puts up flower stems. Below about 41F (5C) it more or less stops but survives, and a well-established clump takes light frost without dying.

So the practical plan is not a single sowing and a single harvest. It is a spring pot cut hard for two months, a defensive summer where you shade it and cut very little, a fresh autumn pot from cuttings for a second good run, and a windowsill pot for slow winter picking. Once you see it that way, the year is easy to manage.

Spring: get a pot established and pinch it

Start as soon as nights stop freezing. Root a bunch of cuttings in a jar, pot three or four of them into an 8 inch (20 cm) pot of firm heavy compost, and stand it in a tray of tap water. Give it full sun at this time of year, and change the tray water every second day. From potting to the first real cut is about four to six weeks.

The single most valuable job of the whole year is pinching in spring. Pinch every growing tip when the stems reach 6 inches (15 cm), and pinch again a fortnight later. Each pinch doubles the number of shoots, so a pot pinched twice before you start harvesting produces several times the leaf of one left to grow up on single stems, and it stays low and dense instead of sprawling.

1. Root cuttings as soon as nights are frost free A jar on a windowsill at 60 to 68F (15 to 20C) roots a bunch in about a week. There is no advantage to waiting for warmer weather; watercress prefers the cool end.
2. Pinch twice before the first harvest Pinch at 6 inches and again a fortnight later. Resist harvesting during this period. The two weeks you give up buys you a far heavier pot for the following two months.
3. Set the water routine now Start changing the tray water every second day from the beginning so it becomes automatic before the weather makes it urgent.

Summer: expect it to turn hot and run to flower

Summer heat is what beats watercress, and it does not fail gracefully. Once root temperature stays above about 77F (25C) the leaves turn harsh and small, the stems go stringy, and the plant sends up branching heads of small white flowers. This is normal behavior, not a mistake, and no amount of feeding or watering reverses it. What you can do is delay it and reduce it.

Move the tray so it gets morning sun and afternoon shade, or stand it on the shaded side of the house. Change the water daily, and refill in the evening with cold water straight from the tap to knock the root temperature down overnight. A deeper tray of water heats more slowly than a shallow one. Cut flower stems out as you see them, since a stem that has flowered will not give you good leaves again. Stop feeding, cut only the tips you actually need, and accept a lean six or eight weeks.

Do not try to save a pot that has flowered right through and gone woody. Take clean tip cuttings from any soft growth left on it, root them in a jar, and treat the old pot as compost. A fresh autumn pot is far better than a nursed one.

Autumn: the second and often the best season

Autumn watercress is frequently better than spring watercress. Cooling nights, softer light and a lower pest pressure give thick dark leaves with a clean pepper. Start a fresh pot from cuttings as soon as the peak heat breaks, so it is established and pinched by the time the good conditions arrive, and return the tray to full sun.

Go back to changing the water every second day and cutting a third of the growth each week. Keep feeding at half strength every fortnight until growth visibly slows, then stop. Watercress that goes into winter with a lot of soft, heavily fed growth suffers more from cold than a slightly harder plant does.

1. Start the autumn pot before the heat has fully gone Root cuttings while summer is ending so the new pot is growing away the moment temperatures fall into the 50s and 60s F. Waiting until the weather is perfect costs you a month of the best season.
2. Move the tray back into full sun The shade that saved the plant in summer now limits it. Autumn light is weak and watercress wants all of it.
3. Stop feeding as growth slows Late soft growth is the part that turns to mush in the first hard frost. Let the plant firm up before winter.

Winter and the record that makes next year easier

An established outdoor pot survives light frost and simply stops growing; the leaves may go bronze and some die back, but the crowns come through and restart in spring. Reduce the tray to a shallow inch of water, change it weekly rather than daily since nothing is growing fast, and stop feeding entirely. Move the tray to a sheltered spot against a wall. In hard-frost regions, bring one pot into a cool bright room and pick a few sprigs from it through the winter.

Winter is also when the notes pay off. Read back through the season and pull out four dates: when you first pinched, when the first proper cut came, the day the leaves first tasted hot, and the day the first flower stem appeared. Those four dates, and the position each pot stood in, are enough to plan next year precisely, and they take two minutes to write down while you can still remember them.