Trim the stems at a 45-degree angle, and place in a glass with two inches of water. Refrigerate for up to two weeks (cover the leaves with an unsealed plastic bag to minimize odor absorption), replacing the water if it gets cloudy.
Dry hardy-leaf herbs like thyme, oregano, rosemary, and bay leaves.
Working with one herb variety at a time, wash thoroughly, blot dry, and spread the leaves in a single layer on a paper towel. Microwave in 30-second intervals, turning leaves over for even drying, until crisp and brittle. Microwave times will vary, but the whole process should take no more than two to three minutes total.
Freeze soft-leaf herbs like dill, mint, parsley, basil, and chives.
Place whole sprigs, chopped leaves, or whole leaves in a tightly sealed plastic bag for up to six months. When cooking, defrosting is unnecessary--just break off leaves and add them to the skillet.
Here is Ann's own tip for the basil: "I like making pesto out of the basil, but if I don’t have time to make it right away, to keep the basil from going bad I pluck the leaves and wash them, then process them in the food processor with olive oil. I put the processed basil in a small deli container, smooth the top and cover with olive oil. This can be refrigerated until I’m ready to make pesto, and then just tossed back in the food processor with the other ingredients."