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SUS Farms · Utah Seed Library

Growing Red Onion in Utah

vegetable · Amaryllidaceae · cool season · 110 days to harvest

Methodtransplant
Days to maturity110 days
Seed depth0.25″
Plant spacing4″
Row spacing12″
Germ. temp50–85°F

Schedule (May 15 last frost · Sevier County)

Start indoors2/20
Transplant out4/17
First harvest8/7

Planting depth, drawn to scale

0"1"2"3"4"5"6"0.25" deep

Step-by-step

  1. 1. Start indoors 12 weeks before last frost. Seed-starting mix in 2-4" cells. Bottom heat at 50–85°F until germination, then drop to room temperature. 14-16 hours of light from clip-lamp 2" from leaves.
  2. 2. Harden off for 7 days. Day 1: 1 hour outside in shade. Add an hour and more sun each day. Skip if windy or below 50°F.
  3. 3. Transplant 4″ apart in rows 12″ apart. Soil should be at least 50°F before planting. Black plastic mulch laid two weeks ahead helps in cool springs.
  4. 4. Mulch and water consistently. 2" of straw or wood chip around the base. Drip line at surface. 1" per week including rain.
  5. 5. Harvest around day 110. Red Wing and Cabernet are reliable long-day reds for Utah. Sweet enough for raw use, store 4-6 months.