Heirlooms are very light feeders. When we divide bulbs, we'll sometimes sprinkle a bit of fertilizer in the hole, then cover it with soil before planting to prevent the bulb from rotting. But most of the time, we just till in a light layer of wood chips that both loosens and nourishes the soil as it breaks down. We leave our bulbs in the ground year-round. We've found that you can plant year-round, also.
Most people plant bulbs in the fall simply because that's when they are available commercially.
Any deeper, and bulbs risk rotting in our damp, clay soil. But bulbs are planted a little bit deeper in cold climates. Daffodils are fragrant, early-flowering, spring bulbs. The term heirloom refers loosely to daffodils existing before 1940. Easy-care favorites, heirloom daffodils grow in full sun to part shade.