Collard greens
Brassica oleracea var. viridis
Also known as: Collards, Tree cabbage, Borekale, Couve
Quick facts
- Category
- leafy greens
- Difficulty
- beginner
- Days to harvest
- 60 to 85 days
- Harvest type
- cut leaves, plant regrows for repeated harvests
- Spacing
- 45 cm between plants
Environment
- Temperature
- 5–28°C
- pH
- 6 to 7
- EC (hydroponic)
- 1.5 to 2.5 mS/cm
- Daily light
- 14 to 20 mol/m²/day
Climate and zones
- USDA zones
- 6 to 11 (winter low around -23°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
Collard greens works in:
- media bed (ebb and flow)
- wicking bed
- soil bed
- drip / Dutch buckets
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 (collard greens works in the media listed below).
| Medium | pH effect | Water retention | Bacterial surface |
|---|---|---|---|
| Expanded clay pebbles (LECA) | neutral / inert | low | high |
| Coco coir (Coconut coir) | slightly acidic | high | moderate |
| 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
An easy and productive hydroponic leafy green that tolerates both heat and cold. EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 15–30°C (one of the few brassicas that performs well in warm conditions; also handles cold down to about -5°C). Moderate to high light (DLI 14-22 mol/m2/day). DWC, NFT, or media bed systems work. The plants are large (60–90 cm tall) and need more space than lettuce or bok choy. From transplant to first harvest: 6-8 weeks. Harvest lower leaves progressively (cut-and-come-again), leaving the growing tip and upper leaves to continue production. A single plant provides harvests every 1-2 weeks for months. The thick, sturdy leaves hold up to long cooking (the traditional method) but can also be eaten raw in salads or massaged with oil and salt for a kale-salad-style preparation. Caterpillars (cabbage loopers, imported cabbageworm) and aphids are common pests; BT spray controls caterpillars. For aquaponics growers, collards are a reliable, low-maintenance, long-producing green that handles the temperature fluctuations of outdoor and semi-outdoor systems.
Plan a setup with Collard greens
Verified against: rhs-uk, university-of-florida-ifas. Last reviewed 2026-05-15.