Last edited on 2 Nov 2026. View history
California Red Onion
A variety of red onion
How to sow California red onion: Direct seed indoors or plant sets (small bulbs) outside.
Sun requirement for California red onion: Plant in Full Sun
A sweet red salad onion, in a strain selected by seed grower Richard Watson in Amuri, inland Canterbury, to keep growing through very cold winters and to produce large bulbs in cold climates. It also does well in warmer areas. It stores well once dried and was still keeping fresh for salads until late June. Sow in trays from February to July (earlier sowing gives bigger onions), transplant at 10 cm diagonal spacing when the tops are 8 to 10 cm high, and harvest in January and February.
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California red onion facts
Lifespan
What are growing degree days?
A plant grows with warmth, not with days. A growing degree day is one day's worth of useful warmth: how many degrees the day's average temperature is above the lowest temperature the crop grows at. Add them up from planting and you know how far along the crop is, whatever the calendar says.
Say that lowest temperature is 10°C. A day averaging 17°C gives 7 growing degree days. A day averaging 8°C gives none, as it is too cold for the crop to grow. That is why the same lettuce takes about 50 days in a summer and 90 in an autumn: it needs the same total warmth either way.
For California red onion, the FAO EcoCrop database gives a lowest growing temperature of 4°C and a shortest growing cycle of 85 days at its best temperature, about 1233 growing degree days to a first harvest.
Where you've told us where your garden is, we use this and the weather there to predict when your California red onion will be ready to harvest. We don't use it for how long a plant lives or when it finishes: we go by what members have logged for that.
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Ecological requirements
Data from the FAO EcoCrop database for Allium cepa L.
| Family / Taxonomy | Liliopsida Liliidae Asparagales Alliaceae |
|---|---|
| Optimal temperature | 12 - 25 °C |
| Absolute temperature | 4 - 30 °C |
| Optimal rainfall | 350 - 600 mm/year |
| Absolute rainfall | 300 - 2800 mm/year |
| Optimal soil pH | 6.0 - 7.0 |
| Absolute soil pH | 4.3 - 8.3 |
| Crop cycle | 85 - 175 days |
| Max altitude | 2000 m |
| Life form | herb |
| Life span | biennial |
| Habit | erect |
| Optimal soil depth | medium (50-150 cm) |
| Optimal soil texture | medium, organic |
| Optimal soil fertility | moderate |
| Optimal soil drainage | well (dry spells) |
| Optimal soil salinity | low (<4 dS/m) |
| Photoperiod | short day (<12 hours), neutral day (12-14 hours), long day (>14 hours) |
| Optimal light | clear skies |
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