Edible plant · roots bulbs

Onion

Allium cepa

Also known asBulb onion · Common onion · Yellow onion · Red onion · White onion · Cebolla · Zwiebel

intermediate cool-season aquaponic-ready single

Use in garden planner

Days to harvest

90–130

Yield / plant

0.2kg

Spacing

10 cm

Daily light

17–25DLI

Environment

The bounded range this crop tolerates.

Temperature

5152535

10–26°C

45.578.5

6–7

EC (hydro)

01234

1.4–1.8 mS/cm

Daily light

5152535

17–25 mol/m²/d

✓Single harvest

Climate and zones

USDA zones: 3–10 (winter low around -40°C)
Frost: frost hardy
Season: cool (spring/fall)

✓Outdoor year-round (in zone)

✓Outdoor in growing season

✓Unheated greenhouse / hoop

✓Heated greenhouse

✓Indoor (heated home)

·Indoor hydroponics + grow lights

Growing systems

Root mass: moderate.

·Deep water culture (rafts)

·NFT channels

·Vertical / aeroponic tower

·Drip / Dutch buckets

✓Media bed (ebb and flow)

✓Wicking bed

✓Soil bed

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 because of the day-length requirement and long season. Use media beds or large containers with about 10 cm depth for roots. EC 1.4-1.8 mS/cm. pH 6.0-7.0. Temperature: 10–26°C. Moderate to high light (DLI 17-25 mol/m2/day). Pick the correct day-length type for your latitude; getting this wrong is the most common beginner mistake. Start from sets (small bulbs, fastest), transplants (medium), or seed (slowest, 100-130 days). Green onions, harvested before bulbing, are far easier and quicker than bulb onions. For bulbing, the day-length trigger starts bulb formation, and before that point the plant must build enough leaf area to support a good bulb (each green leaf becomes one ring). Harvest when the tops fall over and start to dry, then cure the bulbs in a warm, dry, ventilated space for 2-4 weeks before storage. In aquaponic media beds onions grow well, but the long crop time (4-6 months for full bulbs) ties up the bed for a whole 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.