Iceberg lettuce / Crisphead lettuce (Lactuca sativa var. capitata (Crisphead group)) growing guide

Quick facts

Category: leafy greens
Difficulty: intermediate
Days to harvest: 65 to 90 days
Harvest type: single harvest then replant
Spacing: 30 cm between plants

Environment

Temperature: 13–21°C
pH: 5.8 to 6.5
EC (hydroponic): 0.8 to 1.4 mS/cm
Daily light: 13 to 18 mol/m²/day

Climate and zones

USDA zones: 4 to 9 (winter low around -34°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

Iceberg lettuce works in:

deep water culture (rafts)
NFT channels
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 (iceberg lettuce works in the media listed below).

Medium	pH effect	Water retention	Bacterial surface
Rockwool (Mineral wool)	alkaline until pre-soaked	very high	low
Expanded clay pebbles (LECA)	neutral / inert	low	high
Coco coir (Coconut coir)	slightly acidic	high	moderate
Net pot, no medium (Bare-root)	-	-	-
Soil-based mix (Potting soil)	varies by source	high	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	0.6
vegetative	3	1	2	1.2

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

The most challenging lettuce type for hydroponic growing because it requires specific conditions to form a tight head. EC 0.8-1.5 mS/cm. pH 5.5-6.5. Temperature: 12–18°C (narrower range than other lettuce types; above 22°C, the head doesn't form properly and the plant bolts). Low to moderate light (DLI 12-17 mol/m2/day). From transplant to head harvest: 70-85 days (much slower than loose-leaf lettuce). The tight head formation requires consistent cool temperatures and even light; any stress during head formation causes loose, uneven heads or premature bolting. Tipburn (calcium deficiency at inner leaf margins) is common because airflow can't reach the tightly packed inner leaves. For commercial hydroponic growers, butterhead and loose-leaf types are far more practical than iceberg; the long crop time, narrow temperature requirements, and quality challenges make iceberg unprofitable at small scale. For home growers who specifically want iceberg, grow in the coolest season available and choose varieties bred for hydroponic conditions.

Notable varieties

A starting shortlist of cultivars worth knowing about. Not exhaustive: the seed catalogs list hundreds of named varieties. These are the ones home growers commonly choose between.

Cultivar	Type	Days	Notes
Great Lakes 118	open-pollinated	80	1944 All-America Selections winner that established the modern iceberg type. Solid heads, slow to bolt for an iceberg, more reliable in home gardens than most commercial F1s. Still widely available.
Webb's Wonderful	heirloom	75	British pre-1890 crisphead, the classic UK summer lettuce. Sweeter than Great Lakes and more bolt-resistant. The supermarket round lettuce most British shoppers grew up with.
Crispino	hybrid	60	Modern F1 bred for fast heading. Compact, dense heads in two months, useful where the growing window is short. Holds in the field longer before bolting than Great Lakes.
Salinas	open-pollinated	80	The commercial California workhorse for decades. Released by USDA in 1975, named for the Salinas Valley where most US iceberg is grown. Tipburn-resistant under typical field conditions.