Dill seed is the fruit of the dill plant, while dill weed refers to the leaf and stem of the same plant. Dill seed is also known as seed dill and dill weed is sometimes referred to as leaf dill. This plant is in the family Apiaceae, which includes anise, caraway, carrot, celery, chervil, coriander, fennel, parsley and parsnip. The Apiaceae family has over 3,000 members, including the poisonous hemlock. Although part of the same plant, dill seed and weed are so different that expert cooks caution never to substitute one for the other.
Dill weed is herb-like, while the seed is spice-like; the seeds have a stronger flavor than the weed. A fast easy way to use dill in your menus is to add fresh chopped dill to softened butter and use it as a spread on crusty bread or melt the butter as a dip for grilled seafood. Leftover tuna or egg salad makes a great appetizer or snack when put onto crackers and topped with a sprinkle of dill seeds. Fresh dill weed stores well in plastic bags in the freezer, while dill seed should be kept in a covered container in a cool dry place. Dried dill weed is less flavorful than fresh, but holds up better in dishes needing long cooking times.
Although much maligned in French and Italian cooking, which favor fennel, dill weed and seed are widely used in Russian, German, Indian, and Scandinavian cooking. Dill seed and weed are used in distinctly different ways, although both may be used together in foods such as pickles, salad dressings, vinegars, and sauces. The use of this herb in dishes such as potato salad is fairly common in the United States. Dill seeds are used in meat dishes in Indonesia and Malaysia, while dill weed is commonly used in rice dishes there. The seeds are used in condiments in Asia and in breads in Sweden.
The dill plant is bright yellow-green in color, with airy flowered heads and feathery spindly leaves. The heads, called umbels, look like upside-down umbrellas. It grows up to 3 feet (0.9144 meters) tall and imparts a lemony-pine essence with flavors reminiscent of family members caraway and fennel. Its fruit, referred to as seeds, are brown, flat, and oval-shaped. Dill seed contains more oil than dill weed and the seed oil is greasier and stronger tasting than dill weed oil.