This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Two varieties of this are grown, common Sweet and Bush Basil. Both are natives of India, where they and other varieties, we read, are in great repute - the leaves and seeds being used in various forms, medicinally and otherwise. The two sorts we have named are tender annuals. The leaves have a peculiarly strong aromatic smell, resembling cloves, very agreeable to some persons, and quite the reverse to others. They are used for seasoning principally. Both kinds require to be sown in March or April, on a slight hotbed, or in boxes, and pushed on in a temperature of 60° or 65°. Some attention is needful in watering till the plants are fairly up, as they are very liable to damp off. The seedlings may be thinned out if too thick; and when the plants can be handled properly, they should be hardened off a little, and afterwards pricked out in a cold frame, if that can be afforded; if not, in a warm sheltered corner - using light rich soil, and inserting the plants 6 inches asunder. But the final planting should be delayed if the weather is at all cold, as the plants will be apt to go off. As a rule, it will not be found safe to plant out in the open border till near the end of May or the beginning of June. When a frame can be afforded, it may be done sooner.
Water frequently in dry, warm weather, but sparingly at other times, and take the lights off altogether after a while if a frame is used, as Basil, when grown soft, shrivels up to nothing in drying. When the plants begin to flower, a portion should be pulled up by the roots and dried in the shade for winter use. As Basil is generally preferred in a green state, it is sometimes needful to sow successional batches, and to force it during winter. In the latter case the seed should be sown in boxes and pushed on in a vinery or pine-stove, and afterwards transferred to a rather drier and cooler temperature. A box of good plants will serve a good while. Take care to sow as often as needful.