Crosnes

Quick facts

Category

roots bulbs

Difficulty

beginner

Days to harvest

150 to 210 days

Harvest type

single harvest then replant

Spacing

30 cm between plants

Environment

Temperature

7–25°C

pH

6 to 7.5

EC (hydroponic)

1 to 1.6 mS/cm

Daily light

12 to 18 mol/m²/day

Climate and zones

USDA zones

5 to 9 (winter low around -29°C or warmer)

Frost tolerance

very hardy (survives deep cold)

Season

cool (spring and fall crops)

Viable growing environments:

• outdoor year-round (in zone)
• outdoor in growing season (annual)

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

Crosnes works in:

• soil 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 (crosnes 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

Not recommended for pure aquaponics. Fish waste alone doesn't provide enough of the nutrients this crop demands (typically potassium, calcium, or boron). It can be grown in a hybrid system where the reservoir is supplemented with hydroponic-style nutrients, but expect to dose actively.

Care notes

A niche crop requiring soil or deep media bed growing (the tubers form underground along spreading stolons). Not suited to NFT, DWC, or other water-culture systems. Media beds with 15 cm of loose substrate (perlite, expanded clay, or coir) can produce crosnes. EC 1.0-2.0 mS/cm. pH 6.0-7.0. Temperature: 12–22°C (cool-season crop; tuber formation is triggered by shortening day length in autumn, similar to potatoes). Moderate light (DLI 12-18 mol/m2/day). Plant tubers or divisions in spring, 5–8 cm deep. The above-ground foliage looks like a typical mint-family plant (square stems, opposite leaves, 30–40 cm tall). Harvest tubers in late autumn after the foliage dies back. Dig carefully to retrieve the small, fragile tubers. Yields are modest: perhaps 200–500 g per plant. The tubers deteriorate quickly after harvest (they dry out and lose crispness within days); eat or pickle them promptly. Despite the difficulty, crosnes are a fascinating specialty crop with a devoted following among chefs and adventurous eaters. The distinctive spiral shape makes them a conversation piece on the plate.

Further reading

• Best crops for hydroponic beginners
• The Kratky method: grow lettuce with zero electricity