Basil, known botanically as Ocimum basilicum, is a species of fast-growing, warm season herb that is most commonly propagated by seed. According to Purdue University, when basil plants are harvested depends entirely on their intended use, be it for drying, for oil pressing or for uses as a fresh, live herb. For home cultivation, the tender leaves and stems can be pinched or plucked with your fingers or cut with small scissors or secateurs. Depending on your climate, you can get between one and five harvests of basil each year, with warmer climes allowing the greatest number of repeat harvest cycles.
Harvest basil leaves intended for use as a dried herb just before the plant produces its pale lavender or white blooms in the summer and/or fall.
Pick basil plants intended for pressing for their essential oil when the plants are in full flower in summer and fall, or at other times of the year when grown indoors.
Pick leaves for fresh eating anytime after two to four pairs of leaves have established themselves on the plant in the late spring or early summer, carrying through to frost. The leaves can be removed individually, a sprig can be cut from a branch, an entire branch can be harvested from the main stem or the plant can be lopped off entirely, leaving the plant to regenerate itself.