Kale / Curly kale (Brassica oleracea var. sabellica) growing guide

Quick facts

Category: leafy greens
Difficulty: beginner
Days to harvest: 55 to 75 days
Harvest type: cut leaves, plant regrows for repeated harvests
Spacing: 30 cm between plants

Environment

Temperature: 7–24°C
pH: 6 to 7.5
EC (hydroponic): 1.2 to 2 mS/cm
Daily light: 14 to 18 mol/m²/day

Climate and zones

USDA zones: 3 to 9 (winter low around -40°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

Kale works in:

deep water culture (rafts)
NFT channels
media bed (ebb and flow)
wicking bed
drip / Dutch buckets
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 (kale 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	1.6

Companion-growing notes

Heavy uptake of nitrogen. 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

An easy, productive hydroponic leafy green for cool to moderate conditions. EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 10–24°C (cool-season; tolerates heat better than most brassicas but flavor and texture are best in cool weather). Moderate light (DLI 14-20 mol/m2/day). NFT, DWC, media beds, or vertical towers. From transplant to first harvest: 5-7 weeks. Harvest by removing lower leaves (cut-and-come-again), leaving the growing tip and upper leaves to continue producing. A single plant provides harvests every 1-2 weeks for months. Lacinato (dinosaur) kale is preferred by many growers for its flavor (sweeter, less bitter than curly types) and ease of preparation (the flat leaves don't trap dirt and sand like curly kale). 'Red Russian' kale adds color to salad mixes and is tender enough to eat raw. Caterpillars (cabbage loopers, imported cabbageworm) and aphids are common pests; BT spray controls caterpillars. Kale is one of the most reliable, long-producing, and nutritious crops for any hydroponic system.

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
Lacinato (Dinosaur)	heirloom	60	Italian Tuscan heirloom, also Cavolo Nero or "Black Tuscan". Long narrow dark blue-green strap leaves, bumpy texture. Less curly than Vates, easier to chew raw. Cold-hardy to about -10C; sweetens after frost.
Red Russian	open-pollinated	55	Russian heirloom with flat oak-leaf-shaped foliage, purple veins, frilled edges. Tenderest texture of common kales. Less cold-hardy than Lacinato (about -7C) but recovers faster after winter.
Curly Vates	open-pollinated	55	Tightly curled blue-green leaves. The supermarket-bunch kale most US growers know. Productive over a long cut-and-come-again season. Most cold-hardy of the common kales, down to -15C with snow cover.
Redbor	hybrid	55	F1 with intensely curled deep purple leaves. Bred for ornamental use as much as eating; common in winter container plantings. Edible and pleasant; deeper purple after cold exposure.