Onion Utah Yellow Sweet Spanish (Allium cepa) is a large, globe-shaped onion variety known for its mild, sweet flavor and excellent storage capability. It is a long-day onion, best suited for northern climates with long summer days. This heirloom variety produces golden-yellow skin with firm, juicy flesh, making it perfect for fresh eating, cooking, and preserving.

How to Grow Utah Yellow Sweet Spanish Onion

Sowing and Germination

• Starting Indoors: Sow seeds indoors 8–10 weeks before the last frost. Plant seeds 1/4 inch deep in seed trays or containers with well-drained soil. Maintain a temperature of 65–75°F for optimal germination.
• Direct Sowing: In areas with mild winters, sow seeds directly outdoors as soon as the soil can be worked in early spring.

Transplanting:

• Harden off seedlings by gradually exposing them to outdoor conditions for 7–10 days before transplanting.
• Space plants 4–6 inches apart in rows 12–18 inches apart to allow for proper bulb development.

Soil Requirements:

• Prefers well-drained, sandy, or loamy soil with a pH of 6.0–7.0.
• Enrich the soil with compost or well-rotted manure before planting to support growth.

Sunlight:

• Requires full sun for at least 6–8 hours daily.

Growing Utah Yellow Sweet Spanish Onion

Watering:

• Onions need consistent moisture, especially during bulb formation. Provide 1 inch of water per week, increasing in dry conditions.
• Avoid overwatering, as excessive moisture can cause bulb rot.

Mulching:

• Apply a light layer of mulch around the plants to retain moisture and suppress weeds.

Fertilizing:

• Use a balanced nitrogen-rich fertilizer in the early growth stages to promote strong leaf development.
• Once bulbs begin to form, switch to a fertilizer higher in phosphorus and potassium to encourage proper bulb growth.
• Avoid excessive nitrogen in later stages to prevent too much leafy growth at the expense of bulb size.

Pest and Disease Management:

• Watch for thrips and aphids, which can be controlled with neem oil or insecticidal soap.
• Prevent fungal diseases by watering at the base of the plants and ensuring good air circulation.
• Rotate onion crops each year to prevent soil-borne diseases.

Fast Facts

• Latin Name: Allium cepa
• Type: Heirloom, Open-Pollinated, Long-Day Onion
• USDA Zones: 5–12
• Days to Germination: 7–14 days
• Days to Maturity: 100–115 days
• Sunlight: Full Sun
• Spacing: 4–6 inches apart
• Soil pH: 6.0–7.0
• Color: Golden-Yellow

How and When to Harvest Utah Yellow Sweet Spanish Onion

• Harvest onions when the tops turn yellow and fall over, usually after 100–115 days.
• Carefully pull bulbs from the soil and let them cure for 2–3 weeks in a warm, dry, and shaded area with good airflow.
• Once fully cured, trim off the roots and foliage, then store in a cool, dry place. Properly cured onions can last several months in storage.

Onion Utah Yellow Sweet Spanish Seed Saving

• Since onions are biennial, they produce seeds in their second year.
• Allow selected plants to flower and go to seed. Once the seed heads dry, collect them and shake out the seeds.
• Store seeds in a cool, dry place for up to 3 years.

Utah Yellow Sweet Spanish onions are a reliable and delicious choice for any garden. Their mild, sweet flavor makes them versatile for culinary use, and with proper storage, they can last through the winter months. Grow your own and enjoy their crisp, golden goodness all year round! 🌱