Red Onion Seed Details Large, flattened globes have deep purple skin and firm, pink-tinged white flesh with red circles. A long-day variety, the red burgundy onions have a strong flavor and store well. Onions are affected by the amount of light they receive. Long-day onions begin forming bulbs when daylight lasts 14-16 hours. They are usually pungent and often store well for many months. How to Plant Red Onion Sets Because summer daylight hours are longer in the North, long-day onions are usually grown there. This variety is vigorous, productive and adaptable. Red onion sets can be planted outdoors as soon as the soil can be worked in the spring. 80 ct. set.