We like to give the foliage eight weeks before cutting it back, although some say six weeks is sufficient. A good rule is to wait at least until a third of the foliage is brown before cutting it back. Heirloom daffodils perpetuate themselves readily by forming bulblets, and many also self-sow. That's why we see so many jonquils, campernelles, and tazetta-type daffodils around old homesteads, in abandoned fields, and along highway medians. And since the bulbs are poisonous, most predators leave them alone.
Heirloom daffodils like cool, moist springs and baking summers.
They prefer more or less neutral soil but are tolerant of a broader pH range. 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.