Leeks / Garden leek (Allium porrum) growing guide

Quick facts

Category: roots bulbs
Difficulty: intermediate
Days to harvest: 100 to 180 days
Harvest type: single harvest then replant
Spacing: 15 cm between plants

Environment

Temperature: 7–24°C
pH: 6 to 7.5
EC (hydroponic): 1.4 to 2.2 mS/cm
Daily light: 14 to 20 mol/m²/day

Climate and zones

USDA zones: 5 to 10 (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)
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

Leeks works in:

media bed (ebb and flow)
wicking bed
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 (leeks works in the media listed below).

Medium	pH effect	Water retention	Bacterial surface
Soil-based mix (Potting soil)	varies by source	high	high
Coco coir (Coconut coir)	slightly acidic	high	moderate
Expanded clay pebbles (LECA)	neutral / inert	low	high

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.

Stage	N	P	K	EC target (mS/cm)
seedling	1	1	1	0.7
vegetative	2	1	3	1.8

Companion-growing notes

Heavy uptake of potassium. Co-grown crops with the same demand will end up deficient even at "correct" EC. Plan around this in shared reservoirs.

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

A long-season but rewarding hydroponic crop. Deep media beds or large containers (15 cm depth for the root system, plus room for hilling/blanching). EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 12–24°C (cool-season; tolerates light frost). Moderate light (DLI 12-18 mol/m2/day). Long season: 80-120 days from transplant depending on variety. Blanching is important for quality: as the plant grows, mound media, cardboard tubes, or opaque wraps around the shaft to keep it white. Without blanching, the shaft is green and tougher. Harvest when the shaft is 2–3 cm diameter. Baby leeks (harvested young at pencil thickness) are faster (50-60 days) and don't need blanching. The inevitable grit between leek layers (from mounding) requires thorough washing: slice the leek lengthwise and rinse each layer under running water. For commercial growers, baby leeks are more practical than full-sized because of the shorter crop time and premium pricing ($8-15/kg).