A semi-aquatic perennial grown as an annual for its peppery, mineral-rich leaves — equally at home in a pot sitting in a tray of water as in a stream margin.
Nasturtium officinale · also called garden cress, water nasturtium
Windows are counted from the average date of your last spring frost.
Watercress produces harvestable leaves within 4-6 weeks of sowing and regrows reliably after cutting. Its sharp, peppery bite comes from the same compounds that give mustard its heat, making it a distinctive salad and garnish green.
A little history. Native to Europe and western Asia, watercress is a true aquatic or semi-aquatic perennial in the mustard family. It roots readily at stem nodes when in contact with moist soil or water, which is the basis for propagation by cuttings.
Sow seeds 0.1 inch (3 mm) deep, and aim for 6 inches (15 cm) between plants once thinned. Press seeds onto the surface — they need light to germinate. Keep the medium constantly wet, not just moist, until sprouts appear. Seedlings emerge in 5–14 days.
Containers work well — place a pot without drainage holes, or set a draining pot inside a saucer kept filled with water. In containers: 6-inch pot, at least 6 inches deep, kept standing in water.
Keep roots permanently wet — refill the standing water tray daily in warm weather. Water when if the saucer runs dry or leaves wilt slightly, water immediately. Aim for continuous moisture; standing water 1–2 inches deep is ideal.
Side-dress (scatter fertilizer along the row and water in) every 3–4 weeks during active growth. What to use: low-nitrogen liquid feed or dilute compost tea — excess nitrogen produces lush but bland leaves.
Pinch out any flower stems as soon as they appear to extend the harvest window. Cut stems back by one-third after each harvest to encourage dense, bushy regrowth.
It's ready when harvest when stems are 4–6 inches long and carry at least 4–5 true leaves (the full-shaped leaves that follow the first rounded seed leaves). Leaves should be deep green and firm. Cut stems 2–3 inches above the waterline or soil with clean scissors. Take no more than one-third of the plant at a time to allow regrowth. Harvest in the morning when leaves are most turgid.
Stand cut stems upright in a glass of cold water, cover loosely with a plastic bag, and refrigerate. Use within 3–4 days; leaves wilt and yellow quickly once cut.
Sow a new batch every 3 weeks from early spring through midsummer, then again in late summer for fall harvest, to maintain a continuous supply before heat or frost ends the season.
In mild climates where frost is light, submerged or crown portions survive winter and regrow in spring. In hard-freeze climates, treat as an annual and resow each spring.
Spearmint
Both want permanently wet feet, and mint's strong scent can help hide young cress from flea beetles that hunt by smell. Sink the mint in its own buried pot or stand it in a separate tray — left loose it will overrun a shared container within one season.
Chives
The strong onion smell of chives can mask the mustard scent that aphids and flea beetles follow, and their tight upright clumps take up little room next to sprawling cress. Set the chive pot beside the water tray, not in it — chives rot in standing water.
Lettuce
Gardeners have long grown these two salad greens side by side, and the pairing holds mostly because they share a schedule: both are cut young, both sulk above 75F, and lettuce is outside the mustard family so pest pressure is not doubled. No further mechanism is demonstrated.
Spinach
Spinach sends down a central taproot while watercress feeds from shallow roots along its stems, so the two often draw water and nutrients from different levels of a constantly moist bed. Being outside the mustard family, spinach also will not carry clubroot or downy mildew back to the cress.
Radish
Radish is a mustard-family relative, so it feeds the same flea beetles and hosts the same downy mildew and clubroot. Grown together the pest and disease load stacks, and radish needs free-draining soil that dries between waterings — the opposite of what cress wants.
Arugula
Another mustard-family green and a reliable flea beetle magnet; planted next to cress it draws beetles onto both crops and shares the same downy mildew. Keep them in separate containers and cover young cress with fine mesh.
A perennial — it holds its spot for years, so it sits outside the annual rotation.
Grown as a semi-aquatic perennial in its own pot or wet corner, watercress sits outside the annual bed rotation, so there is no family gap to count. It is a moderate feeder that leaves little behind; if you do clear the container, refresh the medium and scrub the tray before replanting.
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