Long-day Onion Plants are best suited for northern gardens, they require 14-15 hours of sunlight to grow. They grow best when planted 1-inch deep and 5-inches apart. Incorporate a good garden fertilizer into the soil at planting. About one month after planting, side-dress the onion plants with ammonium sulphate. We recommend applying it at the rate of 1 cup per 20 feet, repeating every 3 to 4 weeks during the growing season, always water after fertilizing. Stop fertilizing once the bulbs are big enough that they crack the ground. When the tops of the onions have fallen over, they are fully mature and can be pulled from the ground. For complete onion care, read our Don't Cry blog article. Onion plants ship according to your hardiness zone.