This section is from the book "Culinary Herbs", by M. G. Kains. Also available from Amazon: Culinary Herbs, Their Cultivation, Harvesting, Curing and Uses.
Having thoroughly fined the surface of the garden by harrowing and raking, the seeds may be sown or the plants transplanted as already noted. From this time forward the surface must be kept loose and open by surface cultivation every week or 10 days and after every shower that forms a crust, until the plants cover the whole ground. This frequent cultivation is not merely for the purpose of keeping the weeds in check; it is a necessary operation to keep the immediate surface layer powdery, in which condition it will act as a mulch to prevent the loss of water from the lower soil layers. When kept in perfect condition by frequent stirring the immediate surface should be powdery. Yes, powdery! Within 1 inch of the surface, however, the color will be darker from the presence of moisture. When supplied with such conditions, failures must be attributed to other causes than lack of water.
When desired, herbs may be used as secondary crops to follow such early vegetables as early cabbage and peas; or, if likely to be needed still earlier, after radishes, transplanted lettuce and onions grown from sets. These primary crops, having reached marketable size, are removed, the ground stirred and the herb plants transplanted from nursery beds or cold frames.
Often the principal herbs- sage, savory, marjoram and thyme-are set close together, both the rows and the plants in them being nearer than recommended further on. The object of such practice is to get several crops in the following way: When the plants in the rows commence to crowd one another each alternate plant is removed and sold or cured. This may perhaps be done a second time. Then when the rows begin to crowd, each alternate row is removed and the remainder allowed to develop more fully. The chief advantages of this practice are not only that several crops may be gathered, but each plant, being supplied with plenty of room and light, will have fewer yellow or dead leaves than when crowded. In the diagram the numbers show which plants are removed first, second, third and last.
Thinning Scheme for Harvesting