Fortress Onion

$3.99

Fortress Onion is a hybrid, long-day onion with beautiful, dark-brown, globe-shaped bulbs. Stores very well, usually 7-8 months while retaining color. Performs well in clay or muck soils. Allium cepa. 110 days to maturity.

250 seeds per packet

Availability: In stock

Fortress Onion is a hybrid, long-day onion with beautiful, dark-brown bulbs. This is one of the most beautiful onions you’ll find. It is a globe-shaped, sweet onion that stores extremely well, usually up to 7-8 months. The skin retains its dark-brown color very well throughout the storage time. Fortress has a very strong root system and performs well in clay or muck soils.

Fortress Onion can be direct-seeded or transplanted, although we recommend transplanting. For direct-seeding, plant seeds 2″ apart along the row with a row spacing of 24″. Once seedlings emerge, thin seedlings to a 6″ plant spacing along the row. Plethora Onion seeds can be planted with our Hoss Garden Seeder. We recommend using a #1 seed plate and modifying the hole size slightly to accommodate the onion variety being planted. For denser plantings, more holes may need to be drilled to accommodate a thicker spacing.

For transplanting, plant one seed per cell in our heavy-duty seed starting trays. Once the green stems reach 6-8″ in length and/or they can be easily pulled from the seed trays, the transplants are ready to go in the ground. Transplant onions 4-6″ apart along the row with a row spacing of 24″. If drip irrigation is used, onions may be planted on double rows with drip irrigation in the middle. We suggest burying the drip tape 3-4″ deep and planting on both sides of the tape.

Onions are heavy feeders and will require significant nutrient inputs throughout their lifespan. We recommend feeding them with our 20-20-20 and Ammonium Sulfate fertilizers. Fertilize with 20-20-20 shortly after transplanting. The phosphorous and potassium in the 20-20-20 fertilizer will help to promote solid root development, while the nitrogen will promote vegetative growth. Once transplants are established, we recommend side-dressing or injecting with our Ammonium Sulfate fertilizer.  Side dress or inject 1 cup per 20 feet of linear row every 3-4 weeks after transplanting.

Fortress Onion Planting Information

Planting Method: transplant

When to Plant: early spring

Planting Depth: 1/4″

Seed Spacing: 4″

Row Spacing: 12-18″

Days to Maturity: 110

Disease Resistance: Basal Rot, Pink Root

Onion Planting Guide

Select an onion variety based on your geographical location. In many cases, intermediate-day varieties can be grown in southern long-day regions and northern short-day regions.

Short-day Onions

  • Plant in fall and overwinter for a spring harvest
  • Start the bulbing process when day length reaches 10-12 hours

Intermediate-day Onions

  • Plant in late winter for an early summer harvest
  • Start the bulbing process when day length reaches 12-14 hours

Long-day Onions

  • Plant in spring for a mid-summer harvest
  • Start the bulbing process when day length reaches 14-16 hours

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