Planting Guides
When to Plant Onions in Salt Lake City: Complete Guide + Best Varieties for Zone 7a
Salt Lake City, Utah
USDA Zone 7a
Last Frost: Apr 25
Last updated: October 30, 2025
Plant onions in Salt Lake City April 10-24 for Zone 7a. Choose intermediate to long-day varieties like Yellow Sweet Spanish and Walla Walla for best mountain valley results.
— Image © PlantReference.org 2026
Quick Answer
Plant onions in Salt Lake City April 10-24 using intermediate to long-day varieties. Choose Yellow Sweet Spanish or Walla Walla for reliable mountain valley performance.
TL;DR
Plant onions in Salt Lake City April 10-24 for Zone 7a's 173-day growing season. Choose intermediate to long-day varieties like Allium cepa 'Yellow Sweet Spanish' and Allium cepa 'Walla Walla' that thrive in Utah's mountain valley climate. Plant garlic October 15-November 1 using hardneck varieties like Allium sativum 'Music'. Salt Lake City's high altitude and temperature swings require careful variety selection and timing.
Frequently Asked Questions
When should I plant onions in Salt Lake City?
Plant onions in Salt Lake City April 10-24 for optimal results in Zone 7a. This timing allows 2-3 weeks before our average last frost date of April 24, giving plants time to establish while avoiding the worst spring weather. Soil temperature should reach 40°F at 2-inch depth before planting. Later plantings reduce bulb size potential as plants have less vegetative growth time before day-length triggers bulbing in our 15-hour summer days.
What onion varieties grow best in Salt Lake City's climate?
Allium cepa 'Yellow Sweet Spanish' and Allium cepa 'Candy' perform best in Salt Lake City's Zone 7a mountain valley conditions. These intermediate to long-day varieties handle our altitude, temperature swings, and 15-hour summer day length perfectly. Avoid short-day varieties like Texas Sweet—they won't bulb properly at our 40.7°N latitude. Allium cepa 'Walla Walla' also grows well here but requires early harvest and immediate use since it doesn't store long.
Can I plant onions in fall in Salt Lake City?
Fall onion planting is risky in Salt Lake City's Zone 7a climate. While some gardeners succeed with overwintering varieties like Allium cepa 'Walla Walla' planted in late August, our unpredictable winter weather often kills plants. Spring planting April 10-24 proves much more reliable for consistent harvests. Focus fall planting efforts on garlic instead—Allium sativum 'Music' planted October 15-November 1 thrives in our mountain winters.
How deep should I plant garlic in Salt Lake City?
Plant garlic cloves 4 inches deep in Salt Lake City to protect them from our harsh winter temperature swings. Point the clove tip upward and space cloves 6 inches apart in rows 12 inches apart. Add 4-6 inches of mulch after planting to insulate soil and prevent frost heaving. This deeper planting depth compensates for our Zone 7a winter conditions where soil can freeze 12+ inches deep during severe cold spells.
Why are my onions bolting in Salt Lake City?
Bolting typically results from temperature stress or using oversized onion sets in Salt Lake City's variable spring weather. Choose sets smaller than a dime and provide row cover protection when temperatures drop below 28°F (-2°C) after planting. Wrong variety selection also causes bolting—stick to intermediate-day varieties like Allium cepa 'Candy' that handle our day-length and temperature conditions. Large sets are already mature and bolt when stressed by late spring freezes.
When do I harvest onions in Salt Lake City?
Harvest onions in Salt Lake City late July through August when 50-75% of tops fall over naturally. This timing gives plants our full 173-day growing season before our October 14 first frost. Don't bend tops over manually—let plants signal maturity by falling over on their own. Harvest during dry weather when possible, as our afternoon thunderstorms can complicate the curing process needed for long-term storage.
How do I store onions grown in Salt Lake City?
Cure onions for 2-3 weeks in Salt Lake City's dry mountain air before storage. Our low humidity (10-20%) speeds curing compared to humid climates. Store cured onions at 32-40°F (0-4°C) with 60-70% humidity—unheated garages work well if temperatures stay above freezing. Storage duration varies by variety: Allium cepa 'Red Wing' stores 8-10 months, Allium cepa 'Yellow Sweet Spanish' stores 4-6 months, while Allium cepa 'Walla Walla' must be used within 1-2 months maximum.
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Written By
Y
Yuki Tanaka
Yuki is a landscape designer in Salt Lake City who specializes in water-wise gardens that work with Utah's dry climate and alkaline soil. She moved to Utah from Portland, Oregon—a rude awakening for someone used to gardening in rich, acidic soil with reliable rainfall. That transition taught her to rethink everything she knew about plant selection and garden design. Yuki now focuses on intermountain-adapted plantings that combine ornamental grasses, drought-tolerant perennials, and carefully chosen shrubs for year-round interest. She works with homeowners looking to reduce water use without giving up on having an attractive garden. Yuki writes with the clarity of someone who had to learn a new climate from scratch.
