Watercress

Watercress is one of the most nutrient dense foods you can eat, according to the Centers For Disease Control and Prevention (CDC), and some people say it isn’t all that hard to grow. I'm feeling a bit challenged, but here's what I've learned so far.

Healthy watercress plants (Scot Nelson) Public Domain

We all know that watercress does not ship or store well, so growing your own is a great way to keep yourself supplied. While watercress prefers growing near slowly moving water, you can recreate these condition closely enough for a crop of watercress. Unlike most of the species we talk about at The Daily Garden, watercress is an aquatic or semi-aquatic plant. You do not need to create an entire hydroponic growing system, however, to grow your own watercress, you just need to keep the soil wet.

Experts tell us that people have been eating watercress longer than any other leafy vegetable. Ever. Despite its Latin name, watercress (Nasturtium officinale) is no cousin to the popular salad flower from  nasturtium plants. Nasturtiums are Tropaeolum, a unique family, while watercress is a member of the cabbage family. This makes watercress a cousin to mustard, wasabi, radishes, broccoli, and horseradish. This also means that the dreaded, imported cabbageworm (Pieris rapae) will be a major pest of your watercress, should you decide to grow it outdoors. 

Watercress may attract flea beetles and mustard beetles. Whiteflies, spider mites, and snails might also cause problems. On the other hand, if your watercress goes to flower, you will receive the added benefit of attracting hoverflies to your garden. Hoverflies love to eat aphids and thrips, so they are welcome any time! Unfortunately, once a plant flowers, much of the flavor is lost. You will get more seeds, however! By the way, if your watercress does become infested with any sort of pest, simply submerge the entire plant for about an hour.

Do not use composted manure from mammals to feed your watercress. It may contain liver flukes (Fasciola hepatica), which can lead to some really nasty digestive conditions. Manure from chickens and fish emulsion are fine to use on watercress.

How to grow watercress

One recommended way to grow watercress is in a fishbowl or other medium-sized glass container. [Check your local thrift store for something truly unique and inexpensive!] Put a 2 inches of pebbles or rocks in the bottom and fill with water. Sprinkle seeds on top of the water or float a few plants on the water surface. The roots will reach down into the rocks and the hollow stems will bring snip-able greens to the water surface. For extra interest, plant food, and glass cleaning, add an algae eater to the mix!

[Update: I tried using a fish tank and it didn't work as planned. I'm not sure if that's because I started with mature plants or just poor logic. Before the plants died completely, I put them in the wading pool outside that serves as a giant dog watering bowl. We'll see what happens.]

[Update.2: The wading pool didn't work, either, and now the algae eater has gone missing. Now my nearly dead watercress plants are in a container outdoors with some bog sage, which also likes lots of water. Fingers are crossed.]

Another suggested way to grow watercress is in aluminum or plastic takeout trays. You will need one tray that is larger than the other, to act as the base. This is the water storage area. The smaller tray is used to hold the plants, but be sure to poke some drainage holes in it before flipping it upside down and filling it 3/4 full of normal potting mix or soilless potting mix that contains perlite or vermiculite.  Next, sprinkle watercress seeds on top. You can also use purchased watercress that has any sort of root growth. It grows very quickly. Seeds germinate best at 50 to 60°F.

If watercress is being grown in a container, it is important to change the water every few days. The standing water can be used to irrigate other plants. Also, watercress can tolerate morning sun, but it really prefers being in the shade. With all the water needed by watercress, you may want to plant it near the hose. It also makes an excellent windowsill garden plant.

While nutrient deficiencies are unusual for watercress planted in the ground, it is a good idea to have a basic understanding of what those deficiencies look like, so that they can be corrected:

• Potassium - older leaves look scorched on the margins (edges)
• Iron - chlorosis (yellowing) between leaf veins
• Phosphate - plants become darker and stunted

Give your disease-fighting abilities a major boost with watercress! And if any of you have grown watercress successfully, please let me know how!