Broccoli / Calabrese (Brassica oleracea var. italica) growing guide

Quick facts

Category: leafy greens
Difficulty: intermediate
Days to harvest: 70 to 100 days
Harvest type: continuous production over weeks or months
Spacing: 45 cm between plants

Environment

Temperature: 12–22°C
pH: 6 to 7
EC (hydroponic): 1.8 to 2.5 mS/cm
Daily light: 17 to 22 mol/m²/day

Climate and zones

USDA zones: 3 to 10 (winter low around -40°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

Broccoli works in:

drip / Dutch buckets
media bed (ebb and flow)
soil bed

Root mass is heavy - thin-channel systems (NFT, vertical towers) can't hold this crop mechanically, hence the system list above.

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 (broccoli 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	1
vegetative	3	1	2	2.2

Companion-growing notes

Heavy uptake of nitrogen, calcium. Co-grown crops with the same demand will end up deficient even at "correct" EC. Plan around this in shared reservoirs.
High transpiration. Reservoir level will need regular top-ups during fruiting or flowering.

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 moderate-difficulty hydroponic crop that rewards good temperature control. Dutch bucket or media bed systems with 20 cm depth for root development. EC 2.0-3.0 mS/cm. pH 6.0-7.0. Temperature: 15–22°C (critical; above 25°C, the heads become loose, yellow, and bitter; below 10°C, growth stalls). Moderate to high light (DLI 15-22 mol/m2/day). From transplant to main head harvest: 60-80 days depending on variety. Harvest the central head when buds are tight and deep green, before any yellow petals appear. Cut 10–15 cm below the head. Most varieties then produce smaller side shoots (2–5 cm heads) for 3-4 weeks of additional harvesting. Calcium and boron supplementation prevents hollow stem (a common quality defect). Caterpillars (cabbage looper, diamondback moth) are the primary pest; BT spray is effective. For hydroponic growers, broccoli occupies a lot of space for a single head; side-shoot varieties ('Belstar', 'Gypsy') maximize the harvest from each plant. The high nutrient demand and cool temperature requirement make broccoli more suited to fall/winter greenhouse production.