Yellow Sweet Spanish Utah Onion Seeds - (Allium cepa)

Yellow Sweet Spanish Utah Onion - Bred for the West, A Sweet Legacy

Large, sweet, and surprisingly easy to grow – the Yellow Sweet Spanish Utah Onion is a product of purposeful breeding for the arid West. This unique heirloom thrives in its Mountain West origins' challenging conditions and alkaline soils. Its story is one of agricultural ingenuity: blending Spanish sweetness and Dutch hardiness through careful selection to produce a variety perfectly suited to the intense summer sun and long days of northern latitudes.

Details

This onion variety is a substantial onion, often reaching a diameter of 3 to 6 inches and weighing up to two pounds. Slice into it and you'll discover a surprisingly delicate fragrance, quite unlike the sharper aroma of many other onion types. This cultivar produces consistently globe-shaped bulbs that reach a significant size, with outer layers ranging from straw brown to golden, sometimes with a coppery undertone. Inside, the white to yellowish-white flesh offers a beautiful contrast.

Well-suited to USDA hardiness zones 3 through 9, this variety thrives as a 'long-day' onion, using the extended daylight hours of northern summers – 14 to 16 hours – to develop its impressive bulbs. However, it's also adaptable to intermediate-day length zones (12 to 14 hours of daylight) with a crucial adjustment: early planting. Starting seeds indoors 8 to 12 weeks before the last expected frost date allows the seedlings to develop a strong root system and foliage during the increasing daylight of late winter and early spring, maximizing bulb development. This adaptability makes it a versatile choice for gardeners in different latitudes.

Its flavor is what truly sets this onion apart – consistently mild and sweet, even when eaten raw. Adding to its appeal is the satisfying texture – a medium firmness that yields to a pleasant crispness. Beyond the traditional garden bed, the Yellow Sweet Spanish Utah Onion offers surprising adaptability for those with limited space, or who enjoy the flexibility of container gardening. Requiring pots at least 12 inches deep and wide enough to allow about 3 inches around each onion, even those with limited space can successfully grow these substantial bulbs on balconies or patios. Its good storage potential is a significant benefit, allowing you to enjoy your harvest well into the cooler months with proper curing. Gardeners in the Western US, and particularly in Utah, appreciate its reliable performance, where its preference for well-drained, alkaline soils contributes to its reliable performance. This productive onion is generally considered easy to grow, making the reward of large, mild onions readily achievable for many home gardeners.

History

The Yellow Sweet Spanish Utah Onion's development is a story of agricultural ingenuity and regional adaptation. Unlike many heirloom varieties, its origins lie not just in a single introduction, but in a deliberate process of combining the desirable traits of European onions to flourish in the specific conditions of the American West. Specifically, the mild flavor of Spanish onions and the hardiness of Dutch types were integrated through careful breeding at Utah State University (USU). This focus on breeding for resilience resulted in a variety uniquely adapted to Utah's often arid climate and alkaline soils.

The 'Sweet Spanish' lineage, originating from mild and sweet varieties cultivated for centuries in Spain (particularly the Valencia and Andalusia regions), is characterized by a lower level of pyruvic acid. Pyruvic acid is the compound that contributes to the pungent, tear-inducing qualities in onions; lower levels result in a milder, sweeter taste, making these onions excellent for fresh eating. These globe-shaped onions with thinner skins were introduced to North America via colonial trade, gaining wider popularity in the late 19th century with the import of improved cultivars. The Netherlands also contributed the 'Rijnsburger' types, onions bred for their storage ability, uniformity, and resilience in cooler climates. Dutch immigrants introduced these long-day varieties with dense flesh to North America in the late 1800s, establishing a foundation for onion cultivation in northern regions.

In the early 20th century, U.S. breeders aimed to combine the Spanish mild flavor with the Dutch storage potential and cold tolerance, adapting these traits to the long-day growing regions of the northern U.S. and Canada. This effort created the  'Sweet Spanish' onion category and subsequent regional varieties. USU was key in refining the Yellow Sweet Spanish onion for Utah's specific environment. Their agricultural experiment stations selected for crucial traits like drought tolerance (a significant advantage in drier regions) and uniform bulb size (important for consistent harvests), resulting in the Yellow Sweet Spanish Utah Onion, well-suited to the state's long-day growing season, leading to a standardized open-pollinated variety.

The 'Utah' designation signifies this onion's strong connection to the region, similar to Vidalia (Georgia) or Walla Walla (Washington). It reflects the dedication of local growers and the ideal growing conditions of Utah. Events like "Utah Onion Days" underscore its agricultural importance, and commercialization by seed companies has ensured its continued appreciation by home gardeners.

Uses

The true beauty of the Yellow Sweet Spanish Utah Onion lies in its adaptability in the kitchen. Its consistent mildness and inherent sweetness, noted even when raw, make it a natural choice for slicing thinly onto fresh salads, burgers, and sandwiches where a sharp bite isn't desired.

However, its flavor transforms remarkably with cooking, developing exceptional depth and sweetness. One of my most memorable experiences involved slow-smoking these onions in a charcoal-fired Kamado cooker. I simply chopped them, coated them generously with olive oil, and let them cook low-and-slow at about 250°F for six hours, stirring occasionally. The result? A pan full of onions reduced down to a couple of cups of incredible sweet, smoky jamminess – a flavor intensity far beyond quick sautéing. Using this deeply caramelized base for a classic French Onion Soup, following the renowned Le Cordon Bleu Home Collection recipe, was absolutely fabulous and showcased this onion's potential perfectly. 

Beyond slow-cooking or smoking, these large, sweet onions are fantastic grilled alongside summer vegetables (where the edges char slightly while the center softens), roasted until tender and even sweeter, or used as the foundational aromatic flavor in countless soups, stocks, and stews. Their reliable sweetness and satisfying texture make them a dependable star wherever a mild yet flavorful onion is called for.

Companion Planting

Beneficial - cabbage family members, lettuce, tomatoes, carrots, beets, strawberries, and Swiss chard. Marigolds, chamomile, and summer savory are also beneficial companions.

Antagonistic - legumes like peas and beans, as well as asparagus and sage.

Planting and Growing Tips

Plant Yellow Sweet Spanish Utah Onions in full sun, in loose, well-drained soil enriched with organic matter for the best harvest. Start seeds indoors 8-12 weeks before the last frost, sowing them ¼ to ½ inch deep. Space plants 4-6 inches apart, with rows 12-24 inches apart, ensuring a soil temperature between 60 and 85°F for optimal root establishment.

For direct sowing, once the danger of the last spring frost has passed and soil temperatures are consistently above 50°F, you can sow seeds directly into the garden. Plant seeds ¼ to ½ inch deep in fertile, well-drained soil that receives full sun. Space seeds 4 to 8 inches apart, with rows spaced 12 to 18 inches apart.

Fall planting for overwintering takes advantage of their impressive cold hardiness, resulting in earlier, larger bulbs, often harvested in late spring or early summer. Spring planting yields a summer harvest with slightly smaller, but usually sweeter, bulbs. This flexibility allows you to tailor your growing season and harvest, choosing larger bulbs for early summer grilling or sweeter bulbs for mid-summer salads. For the best of both worlds, plant in both spring and fall!

Water consistently, especially during bulb development, keeping the soil moist but not waterlogged. Amend the soil prior to planting, and apply a balanced fertilizer at planting. Side-dress with a nitrogen-rich fertilizer every 3 to 4 weeks until bulbing begins, but avoid high nitrogen fertilizer after mid-July to ensure proper bulb maturation.

Harvest Tips

Harvest when the onion tops begin to fall over and turn yellow-brown, typically 110-130 days from seeding. Cure the harvested onions in a dry, well-ventilated location for 2-3 weeks, allowing the outer layers to dry and toughen. Store in a cool, dry place, away from potatoes, for up to 2-3 months. 

Learn More

• 3 Ways to Grow Great Onions From Seed
• Six Hour Caramelized Onions
• A Tale of Two Onion Soups

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