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.
- Plant in fall and overwinter for a spring harvest
- Start the bulbing process when day length reaches 10-12 hours
- Plant in late winter for an early summer harvest
- Start the bulbing process when day length reaches 12-14 hours
- Plant in spring for a mid-summer harvest
- Start the bulbing process when day length reaches 14-16 hours
– Plant in spring for a mid-summer harvest
– Start bulbing when day length reaches 14-16 hours
– Plant in late winter for an early summer harvest
– Start bulbing when day length reaches 12-14 hours
– Plant in fall if temps are rarely below 20F
– Plant in late winter if temps are frequently below 20F
– Start bulbing when day length reaches 10-12 hours