There is no set time for harvesting the leaves of the dill for use as dill weed. You can use them anytime, including shortly after the plant emerges from the ground. Growers often use the dill weed fresh and harvest it as needed for cooking or pickling throughout the growing season.
Clip the leaves from the plant or clip the entire plant a few inches above the ground. If the entire plant is harvested, the main stem, a hollow plant structure, is commonly discarded. The plant will grow from the root, providing a continued source of dill weed through the summer.
While gardeners and cooks have access to fresh dill weed through the summer, it can also be preserved for winter use. The leaves can either be dried or frozen, depending on the gardener's preference. Freeze the dill weed in sealable plastic bags or dry them with a food dehydrator. Store the dried dill weed in an airtight container.
Dill attracts a variety of butterfly species, as well as some beneficial insects such as bees and lady bugs or beetles. Leaving a few plants standing through the entire growing season gives these insects a habitat. Dill also reseeds itself if the seed head is allowed to mature, allowing the gardener to reap the benefits of the aromatic herb year after year without replanting.