Gardeners plant daffodils in fall. This practice allows the bulbs to develop initial roots to absorb water over the winter months and for the chilly soil temperatures to initiate the formation of the flower bud within the bulb. Placing a mulch layer of 2 to 3 inches over the planted daffodil bulbs insulates the soil, conserves moisture and prevents harsh subfreezing cold from penetrating too deeply into the ground.
If yard trees drop their foliage over the garden to create a natural mulch, you don't need to worry. As long as the leaves don't compact down and become like a glued mat, the daffodil foliage and flower stems will still push upward through them in late winter. Moreover, while the leaf layer may look thick and imposing in fall, they decompose over the winter. If you choose to remove the leaves, do it before snow falls or late winter so your rake tines do not damage emerging daffodil leaves.
In northern parts of the United States where the winters are longer and colder, consider gently pulling back leaves over daffodil beds in late winter. While the leaves acted to insulate the soil over winter and conserve moisture, leaves that remain also can keep the soil from drying out and warming up, delaying daffodil flowering. Carefully lift or blow leaves from the daffodil bed. The added sunlight warms the soil and coaxes leaves up a couple weeks earlier than if still tucked under the leafy mulch layer.
If any leaves remain once the daffodils bloom, rake or brush away debris that shades leaves from sunlight. The daffodil foliage persists into late spring photosynthesizing sunlight to make food and replenish the underground bulb. Unimpeded light onto the foliage ensures healthy bulbs and foliage that wither away earlier, making the area look tidy. Leaf-covered daffodils may look long and leggy with yellow-white color rather than evenly deep green pigmentation.