Pair of Yellow Sweet Spanish Onions on a white background.
Onion Seeds, Yellow Sweet Spanish
Onion Seeds, Yellow Sweet Spanish
Yellow Sweet Spanish Onion rings and dices.
Onion Seeds, Yellow Sweet Spanish
Yellow Sweet Spanish Onions with coins for size reference.
Pair of Yellow Sweet Spanish Onions on a white background.
Onion Seeds, Yellow Sweet Spanish
Onion Seeds, Yellow Sweet Spanish
Yellow Sweet Spanish Onion rings and dices.
Onion Seeds, Yellow Sweet Spanish
Yellow Sweet Spanish Onions with coins for size reference.

Onion Seeds,
Yellow Sweet Spanish

4.910 ReviewsSKU: #ON135Min. seed count: 300
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Description

(Allium cepa). Long day. One of the best yellow onion varieties. This is one of the easiest and most adaptable onions to grow, making it an excellent choice for beginner gardeners. The large fruit easily grows to 1 pound each and with good storage quality. Large Yellow Sweet Spanish is a staple for the home gardener and market farmer looking for a reliable and flavorful heirloom onion.

Growing Tips: Yellow Sweet Spanish onions thrive in well-draining, fertile soil. Incorporate organic matter, such as compost, to enhance soil fertility. Plant in a spot that receives full sun, and keep the soil consistently moist. Applying mulch can help retain moisture and suppress weeds. Side-dress with a balanced fertilizer during the growing season for better growth.

Plant Details

Botanical Name
Allium cepa
Life Cycle
Biennial
Sun Requirement
6–12 hr.
Days to Germinate
7–14
Days to Maturity
100–120
Planting Depth
¼ in.
Plant Spacing
4–6 in.
Ideal Temperature
45–80°F
Frost Hardy
Yes

When to Grow

Start Yellow Sweet Spanish onion seeds indoors 8-12 weeks before the last expected frost date in spring. Transplant acclimated seedlings into the garden 4-6 weeks before the last frost, as onions can tolerate light frosts. As a long-day onion, this variety requires 14-16 hours of daylight to initiate bulbing, making it suitable for northern regions with longer summer days. If you’re not sure how to find your area's day length or first and last frost dates, consult our blog post 'Our Experts Answer Questions, Share Resources.'

How to Sow and Plant

Sow seeds 1/4 inch deep in seed-starting mix. Once seedlings are about 5 inches tall and have been hardened off, transplant them into the garden, spacing them 4-6 inches apart in rows 12 inches apart.

How to Grow

Onions are sensitive to weed competition, so it’s important to keep the planting area weed-free by using mulch or hand weeding regularly. Water regularly, especially during dry spells, but avoid waterlogging. As the bulbs mature, reduce watering to allow the onions to dry out slightly, which helps in curing for storage. Monitor for pests such as thrips and apply appropriate organic controls if necessary.

How to Save Seeds

  • Onions will cross with other onions, and occasionally they will cross with scallion types like Welsh onions and Hi Shi Ko bunching onions. Onions will never cross with leeks, chives or garlic.
  • If you are growing types that will cross, try to isolate varieties by at least several hundred feet or ideally up to one mile.
  • Onions are a biennial seed crop, so you will need to overwinter your first-year roots, ideally by digging them up and storing them for the winter. Replant in early spring, and allow onions to shoot up spikes of purple flowers.
  • Let seeds become dry on the plants. Pick seeds when they are hard and dark black, then bring them indoors to finish drying.
  • Once dry, separate the seeds from the husks or leave them on and plant them husks and all.

FAQ

Can Yellow Sweet Spanish onions be grown in southern climates?

As a long-day onion, this variety is best suited for northern regions with longer summer days. In southern climates, it may not receive sufficient daylight hours to bulb properly.

What are the ideal soil conditions for growing Yellow Sweet Spanish onions?

They prefer well-draining, fertile soil with a pH between 6.0 and 6.8. Incorporating organic matter can improve soil fertility.

How do I know when Yellow Sweet Spanish onions are ready to harvest?

They are ready for harvest when the tops turn yellow and fall over naturally. This usually happens 100-110 days after transplanting.

How do I determine day length and first-last frost in my area?

Check out our blog post: Our Experts Answer Questions, Share Resources for links to online guides.

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