Watercress

Watercress (Nasturtium officinale) sells for $6-9 per pound at specialty grocers and farmers markets (USDA AMS Specialty Crop Market News, 2023), and you can grow it in a plastic tub of water on a porch. No raised bed required. It’s one of the fastest-maturing greens you can grow - harvestable in 30-40 days from seed - and it regrows after cutting like most salad greens. That combination of high price, fast turnaround, and minimal infrastructure makes it worth growing even if you have limited space.

What it actually is

Despite sharing a common name with nasturtium flowers, watercress is not in the genus Tropaeolum (which is what most gardeners mean by “nasturtiums”). Watercress is Nasturtium officinale, in the Brassicaceae family alongside arugula, kale, and mustard greens. The name overlap causes consistent confusion; the plants are unrelated. Watercress has small, rounded leaflets arranged in a pinnate pattern along trailing stems, with a sharp, peppery, mustard-like bite that mellows slightly when cooked. The flavor compounds are glucosinolates - the same class of compounds that give arugula and horseradish their heat.

In the wild, watercress grows rooted in gravel along the edges of cold, fast-moving streams. In the garden, you’re replicating that condition: saturated substrate, cool water, and reasonable light.

The ROI case

A packet of watercress seed costs $2.99 and contains 300-500 seeds. In a single growing season, you can run 3-4 succession plantings 2-3 weeks apart, each yielding 0.25 lb of cut greens from a 12-inch container. At $7.00/lb average retail, each container harvest returns roughly $1.75. That’s modest per-harvest, but the infrastructure cost is near zero - a food-grade bucket or dish tub, water, and 30-40 days. The per-pound production cost is among the lowest of any specialty green you can grow at home.

The caveat: watercress is a low-volume crop. You won’t replace your grocery bill with a single container. The value is in harvesting a crop that retails at $6-9/lb that most people simply don’t think to grow.

Growing requirements

You have two options for growing watercress: container water culture or in consistently saturated soil near a water source.

For container culture, fill a shallow tub, bowl, or bucket with 2-3 inches of inert growing medium (coarse sand, pea gravel, or potting mix) and keep it submerged under 1-2 inches of standing water at all times. Change the water every 2-3 days to prevent stagnation and bacterial buildup, or run a small aquarium pump to circulate it. Sow seeds directly on the surface of the substrate and press them lightly into contact - they don’t need to be buried. Germination occurs at 50-70°F.

For in-ground growing, plant in consistently wet, low areas - beside a rain barrel, at a downspout outlet, or in a low wet spot in the garden. Watercress will not tolerate dry soil for more than a day without wilting and dying back.

Cool temperatures (50-70°F) produce the best flavor. Above 80°F, watercress bolts quickly and turns bitter. Like most brassica relatives, it performs best in spring and fall. In hot climates, it’s a short winter crop.

Soil pH of 6.5-7.5. In water culture, no pH management is needed for short-cycle harvests.

What goes wrong

Bolting is the primary failure mode. Warm temperatures above 75-80°F trigger seed stalk production within days. Once it bolts, the stems go woody and the flavor becomes harsh. Harvest before this point and start a new sowing. There’s no way to reverse bolting.

Water quality matters more than most people expect. Stagnant, warm water in container culture promotes bacterial and fungal growth that rots stems at the water line. Change water frequently or circulate it.

Brown leaf margins usually indicate water stress - even brief periods of drying out damage watercress faster than most greens. Check your container water level daily in hot weather.

Leaf miners - particularly Hydrellia species aquatic leaf miners - can damage leaves in wet conditions. The damage is cosmetic for most home gardeners; infested leaves are still edible. Row cover prevents egg-laying in high-pressure situations.

In natural stream or pond edges, watercress can carry Fasciola hepatica (liver fluke) in areas where livestock graze upstream. This is not a concern for container-grown plants - only for wild-harvested watercress near livestock. Don’t harvest wild watercress from streams in agricultural areas.

Harvest and storage

Cut stems 2-3 inches above the water line when plants are 6-8 inches tall. Leave the lower stems and roots intact - they will regrow and produce another harvest in 2-3 weeks under cool conditions. Store cut watercress with stems in a glass of cold water, loosely covered, in the refrigerator. It holds for 3-5 days this way. Don’t store it in a sealed bag without stems in water - it wilts rapidly.

Watercress is best used fresh: raw in salads, on sandwiches, or as a garnish for rich dishes where its pepper bite provides contrast. It loses much of its character with prolonged cooking.

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Related crops: Arugula, Mint, Spinach

Related reading: Companion Planting Basics - how to structure plantings for mutual benefit in small spaces