Basil, French basil, or sweet basil (Ocimum basiiicum L.), a popular, tender, annual herb of the Lamiaceae family (or Labiatae family), is native to India and Asia. Although also grown as an ornamental plant. basil is cultivated commercially for its green, aromatic leaves, which are used fresh or dried as a flavoring or spice. The essential oil and oleoresin are extracted from the leaves and flowering tops via steam distillation and used in place of the dried leaves for flavoring purposes.
More than 50 species and forms of Ocimum spp. differing in growth habit, color, and aromatic composition have been reported, making the true botanical identity of basil difficult. Ornamental types of basil are commercially available and include types with purple foliage (i.e. Dark Opal) or varying growth habits (i.e. bush basil).
Basil for the fresh market should have a sweet flavor and dark green foliage. Commercially, there are three major types of basil having essential oil or dried leaves as their end product. French basil, reputed to be sweetest in flavor and darkest in color, is the most valued. American basil, noted for its rich color, sweet flavor, cleanliness, and uniformity of particle size, is considered to be of very high quality. Egyptian basil also known as Reunion or African basil has a somewhat camphoraceous fragrance and different flavor and so is considerably less expensive.
While basil seed is plentiful, care must be observed in obtaining a type that has desirable characteristics. Because several basil types may be mixed together either by a seed house or processor to achieve a desired blend, any collected seeds that are later sown may vary in their growth, development, and aromatic properties.
Basil can be direct seeded or transplanted to the field in late spring after all danger of frost has passed. The germination rate of the seed should be 80-95%, and seed should not be planted if the germination percentage is less than 70%. If the soil is heavy, the seed should be covered with an anticrustant. The soil should be kept moist to hasten germination and to ensure a more uniform plant stand. The seed is relatively small, and a good friable, well-tilled and uniform seedbed is required for optimum plant establishment. Seeds should be planted only 1/8 - 1/4 inch deep. Plant emergence should occur between 8-14 days. To encourage lateral branching and growth, the tops of transplants can be trimmed prior to field planting, when they are about 6 inches tall.
While the optimum population density is dependent upon the end use, a higher density can be grown if compatible farm equipment is available for mechanical cultivation and seeding. Rows 24 to 36 inches apart, with plants spaced every 6 inches in each row, are recommended Basil can also be planted in a bed of 3 rows 12 inches apart with 12 inches between rows. The distance between the beds, ranging from 24 to 36 inches, is dependent on available equipment. Large variations in growth and yield may occur due to climate conditions, plant type, and cultural and management practices.
The rate of fertilizer application will depend upon soil type and prior history (previous crop and fertilizer application). It is suggested that an N-P-K ratio of 1-1-1 be used. This can be accomplished by a broadcast and plowdown application of N-P2O5 -K2O at a rate of 120- 120-120 lbs. per acre. A sidedress application with nitrogen, at a rate of 15-30 lbs. N per acre, is recommended shortly after the first harvest.
Basil is not tolerant to water stress. A regular and even supply of moisture via trickle or overhead irrigation is necessary. If trickle irrigation is employed, care must be observed during harvest so as not to damage the irrigation line.
Presently, high plant populations of basil coupled with mechanical cultivation are recommended. Commercially labeled herbicides for weed control in basil fields are not available in most states. The presence of weeds in fresh or dried basil leaves decreases the quality of the finished product.
There are several insects and diseases that may infest the plant, but there are no pesticides currently available for use on basil. Plants should therefore be monitored continually for the presence of insects and diseases. The county Extension office should be contacted for information on the identification of insects and diseases and for recommended controls.
The plant part harvested depends upon the projected use. Where basil is grown for its dried leaves and the extraction of essential or volatile oil, it is cut just prior to the appearance of flowers. In the Mediterranean area and in other countries with similar climates, basil is grown as a short-lived perennial, and 3-5 cuttings or harvests per year are achieved. In the more temperate zones basil may be cut only 1-3 times. The first harvest in this case is very low, and the second occurs just prior to open bloom. Generally, basil is harvested for its leaves, sold fresh or dried. The foliage should be harvested, but only above the bottom two to four sets of true leaves.
A sickle bar gerry mower with an adjustable cutting height can be employed to cut the herb. Leaves can be harvested when needed. The foliage should be cut at least 4-6 inches above the ground to allow for regrowth and a subsequent crop. To ensure a continuous supply of leaves, the field harvests and/or planting dates can be staggered accordingly.
Leaves should first be washed and cleaned, with weeds and extraneous materials removed. The quality of basil is determined by color and aroma retention. For the fresh market, only the highest quality plant material should be sold. Prior to milling or distillation, the leaves and/or flowering tops should be dried at low' temperatures (below 40° C) to retain maximum color.
Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.