Onion
Allium cepa
Also known asBulb onion · Common onion · Yellow onion · Red onion · White onion · Cebolla · Zwiebel
Environment
The bounded range this crop tolerates.
Climate and zones
- USDA zones
- 3–10 (winter low around -40°C)
- Frost
- frost hardy
- Season
- cool (spring/fall)
Growing systems
Root mass: moderate.
Growing media
| Medium | pH effect | Retention | Bacterial surface |
|---|---|---|---|
| Soil-based mix (Potting soil) | varies | high | high |
| Coco coir (Coconut coir) | slightly acidic | high | moderate |
Nutrient demand by stage
NPK ratios are relative weights. EC targets shift through the plant's life.
| Stage | N | P | K | EC (mS/cm) |
|---|---|---|---|---|
| seedling | 2 | 1 | 1 | 1 |
| vegetative | 2 | 2 | 3 | 1.6 |
Companion-growing notes
- Heavy uptake of phosphorus. Co-grown crops with the same demand will end up deficient even at "correct" EC.
- Releases root compounds that can inhibit other crops in a shared reservoir.
Aquaponics suitability
Compatible
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 challenging hydroponic bulb crop due to the day-length requirement and long growing season. Media beds or large containers with 10 cm depth for root development. EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 15–25°C. Moderate to high light (DLI 14-22 mol/m2/day). Choose the correct day-length type for your latitude; this is the most common beginner mistake. Start from sets (small bulbs, fastest to harvest), transplants (medium), or seed (slowest, 100-130 days). Green onions (harvested before bulbing) are far easier and faster for hydroponic systems than bulb onions. For bulb onion production: the day-length trigger initiates bulbing; before that point, the plant must have grown enough leaf area to support a good-sized bulb (each green leaf corresponds to one ring in the bulb). Harvest when the tops fall over and begin to dry. Cure bulbs in a warm, dry, ventilated space for 2-4 weeks before storage. For aquaponics media beds, onions grow well but the long crop time (4-6 months for full bulbs) means the bed is occupied for an entire season.
Notable varieties
| Cultivar | Type | Origin | Days | Notes |
|---|---|---|---|---|
| Yellow Sweet Spanish | open pollinated | 110 | Long-day, large yellow bulb, mild flavor, stores 3-4 months. Standard northern-latitude home garden onion. | |
| Walla Walla | heirloom | 125 | Long-day sweet onion (Italian origin via the Pacific Northwest). Very large, very mild, very poor storage (1-2 months). Specifically a fresh-eating onion. | |
| Vidalia (Granex) | open pollinated | 110 | Short-day sweet onion. The original Vidalia onions are this variety grown in Vidalia, Georgia (a protected designation). Other regions can grow Granex but legally can't call them Vidalias. Poor storage. | |
| Red Wing F1 | hybrid | Bejo | 115 | Long-day red storage onion. Stores 5-6 months, holds color through cooking, hybrid vigor gives better disease resistance than open-pollinated reds. |
| Candy F1 | hybrid | 100 | Day-neutral, sweet yellow. The variety to grow if you're in the awkward zone-6-to-7 latitude where short-day and long-day types both struggle. |