Days to Maturity: Approximately 100-102 days from transplant to harvest.
Sun Needs: Full sun with at least 6-8 hours of direct sunlight daily—essential for good bulb size, color development, and flavor in Utah's sunny climate.
Season Type: Cool-season crop with bulbing triggered by day length; transplant in early spring (late March to mid-April in the Salt Lake City area) when soil is workable and temperatures are above 40°F for steady growth.
Plant Habit & Support: Upright, single-stemmed plants reach 12-18 inches tall; no support needed—space 4-6 inches apart in rows 12-18 inches apart for proper bulb development and airflow.
Other Notes: Vigorous and relatively easy to grow with good disease resistance; watch for thrips, onion maggots, or downy mildew—organic mulch (like straw or compost) helps retain moisture and suppress weeds; harvest when tops yellow and fall over for best storage quality.
Best Planting Method: Transplant in early spring when soil is workable and dry enough to avoid compaction. Space plants 4-6 inches apart in rows or beds; plant at the same depth as in the pot or slightly deeper to encourage strong roots. Amend soil with compost for fertility and excellent drainage—raised beds are ideal in heavier or alkaline Utah soils to prevent rot and improve performance. Organic mulch (such as straw, compost, or grass clippings) around plants retains moisture, moderates soil temperature, and suppresses weeds.
Watering Needs: Provide consistent, even moisture (about 1 inch per week) especially during bulb formation—drip irrigation is best in dry Utah conditions to keep foliage dry and reduce disease risk. Avoid overwatering or letting soil dry out completely, as both can cause splitting or poor bulb quality; mulch helps maintain steady moisture during hot spells.
Fertilization Needs: Incorporate compost or balanced organic fertilizer (e.g., 10-10-10) at planting for nutrient-rich soil. Onions are moderate feeders—apply a light side-dressing with a balanced or higher-phosphorus formula midway through growth if needed, but avoid excess nitrogen late in the season to prevent soft tops and encourage bulb development. Harvest when about half the tops have fallen over—gently pull or dig, cure in a dry, shaded spot for 1-2 weeks, then store in a cool, dry place for 4-6 months of good keeping quality.