Short version:
A punchy, mustardy perennial salad leaf with small white flowers that tastes much more benign when cooked. It is low growing, roots all over the place, does well in some shade and can feed you in winter.
Nasturtium officinale is its Latin name, though it isn’t closely related to nasturtiums, which have the Latin name Tropaeolum majus. They are similarly spicy when eaten raw, but come from different families.
Growing watercress
You can see it hugging the ground and spreading itself out.
First things first – watercress does not need to grow in water. You do need soil that has plenty of organic material though, as it needs to be able to retain water well. It also gets rather sulky when you don’t water it enough and rewards your neglect by being tougher to eat and spicier. That is not a problem for most of the year here in the UK. It can grow in pots, in raised beds or straight in the ground and it deals well with shade and sun. It prefers a light shade, but we have an unexpected watercress patch in the sunnier front garden that does better in winter. I call it unexpected as it grew itself from some hole composted watercress. I didn’t have the heart to remove it, but now I love that it invaded this spot.
Watercress growing around an artichoke plant. The watercress started growing from a stem that was chucked into the compost tub. This was taken on the 19th December so this is a helpful little salad green in the winter.
Little white shoots just starting to grow where the stem had touched the ground.
You can grow it from the tiny seeds which can be sown in late winter / early spring. Alternatively, they grow well from cuttings. You can even see it when you buy bags of salad with watercress. Sometimes you see little white roots at the leaf nodes. The plant will happily send out these little roots wherever the stems touch the soil or water sources.
The plant can grow to 15cm but generally it will happily creep along the surface of the soil, anchoring itself with its roots as it goes and forms a wonderful edible ground cover. It keeps the garden from looking barren in the winter and provides a welcome source of green nutritious leaves through the colder months. Because it does well in part shade, as the plants fill out in the spring it continues to do OK. It’s only when light is completely blocked out by other plants thriving in the summer or when the flowers develop it will start to perform badly. In winter it can go a little purple or die back a bit when the weather is freezing. It doesn’t seem bothered by a few overnight frosts.
Under the cavelo nero and around the strawberry plant is watercress. In March after prolonged freezing you can see a mat of yellow stems. You can see that some stems have survived though.
After the watercress dies back after very cold weather or after it has flowered it can recover. It is therefore a useful perennial and if left to its own devices it will propagate itself in its creeping, rooting manner. I sowed the seeds in spring 2017, ready to take with us as we moved. I then planted into its semi shaded spot in a raised bed in the back garden that summer (I would have planted it sooner had we been able to move in sooner). Since then it has happily spread, and I have been happily eating it since. I don’t do any work with the watercress beyond harvesting.
Harvesting watercress
You can start harvesting as soon as you think your plants can provide you with enough to eat. Try not to pull the whole plant out, though you might find yourself pulling at roots where the stems have started to root. It’s a good way to keep it in check though. I harvest either with scissors or by severing the stems with a fingernail. I’ve found that where the watercress hangs over the edge of raised beds or borders, the stems don’t seem to develop roots as well and harvesting is easier. Roots also don’t taste great.
Over the border the stems are lush and have very few roots 
These stems that have made their way out of the raised beds are really easy to harvest
Harvesting flowers is a good idea as they are tasty and prolongs the harvesting period. Once the plant produces seed it isn’t much use for eating until it recovers late autumn / early winter.
Eating watercress
Watercress can be eaten raw as a salad leaf, but I find it hard to eat much due to its spiciness. My other half and little one will not touch the leaves when they are raw. Little one has tried several times to eat the flowers. She knows they’re edible and keeps checking to see if they taste as good as they look. The reaction is always the same. She spits them out and gets rather sad. I like to think that it’s a sign that she’s going to be a scientist… the need to keep testing. The flowers basically taste similar to the leaves with a slightly sweet hint. The roots are bitter so best avoided.
The watercress flowers are the tiny white ones at the bottom right. 
It’s easier to harvest whole stems as opposed to leaves.
I find that everyone is happier if they are blanched or added to soups. You can make a yummy (and very green) soup from watercress. I’m rubbish at following recipes so I won’t give you a proper one but you basically:
Soak your watercress in salted water to remove slugs and bugs. Rinse. 
Fry an onion and some garlic. 
Add a couple of chopped potatoes and stock. Boil till soft 
Add the watercress and bring back to the boil. 
It will reduce by some margin. Simmer for 2 mins. 
Blitz with a handheld blender. 
Makes a lovely smooth soup. 
You can add cream and black pepper. 
My husband geeked out and took a thermal photo of his bowl.
Not a Horticulturist 
I’ve tried growing watercress a couple of times now, indoor in a hydroponic system. The plant does great, maybe even too great in a away as it forms the little white roots all over, but literally all over the stems, even though those places are not touching water (an dobvisouly not any dirt either). Any ideas on how I can prevent the plants from doing this? As it doesn’t taste as nice with all the roots.
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Hello Violien. I’m afraid I don’t have a definite answer for you, but maybe it’s to do with humidity. I know that when I’ve rooted fig cuttings, they do really well in a sealed plastic bag (to increase humidity) with a little bit of water at the bottom. The roots on the fig often form on the leaf nodes above the water, but don’t form there when not covered with a bag. Maybe watercress is similar with humidity. I’ve also read that potassium and phosphorus stimulate root growth, and watercress doesn’t have high nutrient needs. Maybe you’re providing conditions that are too favourable so it wants to go forth and propagate. Not sure if that’s at all helpful, but good luck. It’ll be lovely to hear how it goes. It’s fab hearing from another watercress fan.
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