Watercress

[extremegardener]

It took quite a few years, but we have watercress pretty well established in a long swale that always has at least some running water.
The big problem is weed competition - peppermint, horsetail, sedge, and all in muck, so digging/pulling out the weeds is not a realistic approach.
In the summer, the competition grows taller while the cress is just above the water level, so I scythe the swale a couple of times and that helps.
We have a little bridge (about 3' wide) over the swale, and the watercress is nearly weed free in the shade of the bridge.
Another thing I've tried is dumping wood ash upstream in the swale. Watercress likes alkalinity and can tolerate ph levels that other plants can't. I'm not sure that this has helped, but maybe..
Watercress really comes into its own here when everything else is snow covered in November and December, and sometimes into January.

[johno]

That's good! We're lucky to have it compliments of mother nature. Funny you mention it's weed free in the shade - ours grows where the spring water flows down to the creek and it's in heavily shaded forest floor. No weeds.

[extremegardener]

Thanks Johno for confirmation of the shade thing. Always good to hear other gardeners confirm one's observations and theories. Now I have to figure out how to get more quick shade over the swale...

[Joseph Lofthouse]

Watercress grows wild here, in full sunlight without weeds. It grows in springs from limestone. It thrives in fast flowing (gallons per second) cold (55F) water. I'd guess around 12" to 18" deep.

[johno]

Our spring comes out of limestone also. Temp is about the same, too. But the flow is usually less than 12" deep.

[bertiefox]

We're lucky to have it by the back door where a little spring comes out, but the flow is very slow, just a trickle. The water is also full of minerals and we get a reddish algae in the water, which I guess is iron based. We hate to think it might be agrichemicals and too much nitrogen!
Like ExtremeGardener, it is difficult to keep the weeds under control, especially at this time of the year. We find the best time to harvest is around now when it starts to grow away, but you must keep it cut to prevent it going to flower and seed.