Watercress

Quick facts

Category

leafy greens

Difficulty

beginner

Days to harvest

35 to 50 days

Harvest type

cut leaves, plant regrows for repeated harvests

Spacing

15 cm between plants

Environment

Temperature

10–20°C

pH

6.5 to 7.5

EC (hydroponic)

0.4 to 1.8 mS/cm

Daily light

10 to 16 mol/m²/day

Climate and zones

USDA zones

6 to 11 (winter low around -23°C or warmer)

Frost tolerance

tolerates light frost

Season

cool (spring and fall crops)

Viable growing environments:

• outdoor year-round (in zone)
• outdoor in growing season (annual)
• unheated greenhouse / hoop house
• heated greenhouse
• indoor (heated home)
• indoor hydroponics under grow lights

USDA zone bounds reflect outdoor year-round survival. Anywhere outside the bounded zone range, this crop still grows as an annual in the warm months (outdoor_seasonal), under cover (greenhouse), or indoors under lights.

Growing systems

Watercress works in:

• deep water culture (rafts)
• NFT channels
• media bed (ebb and flow)
• wicking bed

Growing media

The substrate the roots sit in. Choice depends on the system (clay pebbles don't fit NFT channels; rockwool isn't used in media beds) and the crop (watercress works in the media listed below).

Bacterial surface area matters for aquaponics: clay pebbles, lava rock, and pumice double as biofilter substrate. Low-surface media (rockwool, perlite, pea gravel) work in hydroponics but need a separate biofilter in aquaponics.

Nutrient demand by stage

NPK ratios are relative weights at each growth stage; the nutrient mix calculator scales them to absolute grams or ml. EC targets shift through the plant's life: seedlings need a much lighter solution than fruiting adults.

Aquaponics suitability

Compatible with typical aquaponics nutrient profiles. Fish waste provides enough nitrogen for healthy growth; supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.

Care notes

One of the most naturally suited crops for aquaponics, given its native habitat of nutrient-rich flowing water. NFT or shallow raft systems replicate the natural growing environment perfectly. EC 0.8-2.0 mS/cm. pH 6.0-7.5. Temperature: 10–22°C (cool-season; above 25°C, the plant bolts and the leaves become very peppery). Moderate light (DLI 12-18 mol/m2/day). From seed or cutting to first harvest: 4-6 weeks. The plant spreads by rooting at nodes along the stems; a small starter amount colonizes the growing channel rapidly. Harvest by cutting the top 10–15 cm of growth; the plant resprouts from the cut stems. The flowing water of NFT and aquaponics systems produces the cleanest, crispest watercress. Watercress from stagnant water can harbor liver fluke (Fasciola hepatica) parasites in areas where the parasite is present; clean flowing water eliminates this concern. For commercial hydroponic growers, watercress commands premium prices ($8-15/kg) and the connection to flowing water systems makes it a natural aquaponics crop.

Further reading

• What to grow in an aquaponics system (and what won't work)