Spinach / English spinach (Spinacia oleracea) growing guide

Quick facts

Category: leafy greens
Difficulty: intermediate
Days to harvest: 40 to 50 days
Harvest type: cut leaves, plant regrows for repeated harvests
Spacing: 15 cm between plants

Environment

Temperature: 10–20°C
pH: 6 to 7
EC (hydroponic): 1.8 to 2.3 mS/cm
Daily light: 14 to 18 mol/m²/day

Climate and zones

USDA zones: 5 to 9 (winter low around -29°C or warmer)
Frost tolerance: frost hardy (handles regular 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

Spinach works in:

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 (spinach 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	0.8
vegetative	3	1	2	2

Companion-growing notes

Heavy uptake of calcium. 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 fast but fussy hydroponic green. EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 10–20°C (critical: above 22°C, spinach bolts within days; sustained heat is the primary production challenge). Moderate light (DLI 12-17 mol/m2/day; excessive light and long photoperiods trigger bolting). NFT, DWC, raft, or vertical systems. From seed to baby spinach: 3-4 weeks. Full-sized: 5-7 weeks. Succession plant every 2 weeks for continuous supply. Slow-bolt varieties ('Space', 'Renegade', 'Bloomsdale Long Standing') extend the harvest window but can't overcome sustained heat. For year-round production, spinach is a fall/winter/spring crop; summer alternatives include Malabar spinach, New Zealand spinach, or heat-tolerant chard. Downy mildew (Peronospora farinosa f. sp. spinaciae) is the most serious disease; resistant varieties are essential for commercial production. Baby spinach commands $6-12/kg retail and is one of the highest-demand hydroponic salad crops.