Onion
Allium cepa
Onions are a reliable cool-season crop for coastal subtropical gardens when the right variety is planted at the right time. Early establishment, full sun and steady growth are the keys to producing well-sized bulbs.
Overview
At a Glance
Peak Planting Window
May to September
Seasonal Role
Cool-season bulb crop
Difficulty
Moderate
Planting Method
Direct sow or transplant
First Harvest
20–28 weeks
Sun
Full sun
Water
Moderate
Heat Tolerance
Moderate
Humidity Tolerance
Moderate (good airflow recommended)
Family
Amaryllidaceae
Category
Vegetable
Planting Calendar
Monthly Planting Guide
Month-by-month suitability for coastal subtropical Australia.
Rationale
Why This Planting Window
Onions establish best through the cooler months, when mild temperatures support steady leaf growth before bulbs begin to enlarge as day length and warmth increase. Planting too late can reduce bulb size, while hot conditions can stress young plants.
Reference
Growing Information
Lifecycle
Biennial grown as an annual
Ideal Soil Temperature
10–24°C
Germination
7–14 days
Transplant Ready
6–8 weeks
Soil
Loose, fertile, well-drained soil enriched with mature compost
Soil pH
6.0–7.0
Plant Spacing
8–12 cm
Row Spacing
25–30 cm
Frost Tolerance
Moderate
In the garden
Plant Care
Feeding
Prepare the bed with mature compost before planting. Apply a balanced feed during early leafy growth, then reduce nitrogen once bulbs begin enlarging so the plant directs energy into bulb development.
Watering Guidance
Keep the soil evenly moist during establishment and active growth. Reduce watering as bulbs mature and stop once the tops begin to fall, allowing the bulbs to dry before harvest.
Avoid Nearby
- Climbing beans and other legumes are commonly kept separate from onions
Watch out for
Problems & Prevention
Common Pests
Onion thrips, aphids, cutworms, onion maggots and nematodes.
Common Diseases
Downy mildew, purple blotch, basal rot, white rot and bacterial soft rot.
Common Mistakes
Planting the wrong variety for local day length, sowing too late, overcrowding seedlings, overfeeding with nitrogen, inconsistent watering and harvesting before bulbs are mature.
Picking
Harvest
First Harvest
20–28 weeks
Harvest Window
Harvest once bulbs are mature and tops begin to fall naturally
Harvest Indicators
Harvest when most tops have yellowed and fallen naturally. Lift the bulbs carefully, then cure them in a dry, shaded, well-ventilated place before storage.
Standard
SGGS Details
Subtropical Gardener Growing Standard — profile metadata.
- SGGS Code
- VEG013
- Version
- 1
- Confidence
- High
- Seasonal Role
- Cool-season bulb crop
- Crop Champion Month
- June
Explore