While growing herbs in a separate little herb garden is an appealing idea, it is even easier to tuck them here and there in the larger garden. This can turn into a nice spring weekend project that you might actually begin and finish on schedule.
One note of caution: You must be sure to plant any herbs that are going to be eaten where they will not get sprayed if you use insecticides in the garden.
At every nursery, a little bench space is devoted to herbs. Actually, many of the herbs sold as such are not intended to be eaten, but are being sold as ornamental plants. Their herbal history is medicinal and not culinary. If you read the labels, you'll see that it was used to cure this and that and at best might make an interesting tea.
All herbs are in fact very ornamental and in this sense very useful in the garden, even if you don't use them to flavor food. It is difficult for me to imagine not growing thyme in the garden, even if we never used it in cooking (but we do, all the time). I like to grow it along paths, or between paving stones where it softens the hard edges of the paving and perfumes the air with a Mediterranean scent every time it accidentally gets stepped on. If you look on that nursery bench, you'll discover dozens of interesting thymes.
To plant thyme between stepping stones or other pavers, you need a gap wide enough to squeeze a trowel into. Simply excavate several inches of soil, put it in a little pile and then mix in about half as much sand.
All herbs do best grown on the lean side, which intensifies their flavor. The easiest way to put them on a diet is to add lots of sand to the soil. Remember that many herbs have a Mediterranean ancestry and are accustomed to coarse, poor soils and a meager existence. Nothing ruins an herb faster than fertilizer or too much water.
There are a few exceptions. Mints love water, and around a leaky garden faucet is the perfect place to plant mints, though they will soon hide the faucet with their lush growth. Be forewarned that some people consider mints a weed of significant stature, but it is such an important ingredient in iced tea that its bad traits should be tolerated.
Other herbs that like moisture, but not necessarily a good soil, include basil, chamomile, chervil, parsley, shiso, sorrel, sweet woodruff and of course, watercress. With the exception of watercress--which should really be grown on the edge of a pond--these herbs like soil as moist as you would provide for most annual flowers, but no wetter.
Almost all other herbs should be kept somewhat on the dry side. All herbs do best, in my book, with sand added to the soil.
Here are some of my favorites:
Fennel is a weed along much of the Southern California coast, but controllable in the garden if you don't let it scatter its seeds. The leaves and seeds have a licorice flavor and fragrance and the plants are tall (to eight feet) and narrow and very dramatic at the back of a flower bed. The kids call it "licorice plant" and like to chew on the leaves. So do the brightly striped larva of Monarch butterflies.
Catnip is pretty much ignored by my cats but it makes many spikes of very pretty pale lavender flowers all summer long. In the fall, I cut it to the ground or it becomes straggly. The English grow it in front of roses to hide the lower, leafless stems.
Chives are among the prettiest of all bulbs with their pink flowers and are elegant beside a path. Comfrey has the opposite effect, its very big, bright green leaves being very dramatic--a big asterisk in the garden.
Lemon verbena has the most delightful and innocent of all herbal fragrances, though I haven't the foggiest idea what you use it for, now that it is no longer a perfume for young girls who live in little houses on the prairie.
Marjoram, oregano, rosemary, savory, winter savory, and tarragon are the most used by my wife, and since I am not a cook I can only testify to how good they taste once they have added their magic to our meals. I do know that the pizza I like best, from Anna's in West Los Angeles, is full of oregano, and that the winter savory is always getting cut in my garden before it has a chance to flower, which is too bad because it has the prettiest little white flowers.
So what do you plant, and where? My suggestion would be to buy the herbs that appeal to you at the nursery, then load them in a box and walk around the garden looking for likely places.
When you spot a good place for an herb, put it there, come back later and prepare the soil by adding sand and then plant. Be sure to buy a couple of bags of sand at the nursery or a building-supply store.