Basil should receive a thorough watering each week. Soak the ground until the soil is wet to a depth of approximately 1 1/2 inches. Like most other herbs, basil requires moist soil but doesn't like sitting in puddles. And basil has shallow roots, so they require more frequent watering than do other plants—at least once each week during periods with no rain. Always water the soil, not the plant leaves themselves, because wet leaves can lead to fungal rot or disease.
Basil grows best in well-drained soil. When growing in pots, line the bottom of the pot with 2 inches of gravel to allow adequate drainage from the pot. And make sure your pot has drainage holes in the bottom. Without this drainage assistance, water can remain in the pot and rot the basil plant's roots.
If you are growing basil for cooking, it is ideal to get for plants to have as many leaves as possible. To do so, fertilize your basil weekly with a nitrogen-rich fertilizer. Nitrogen is the nutrient that fuels green leaf growth, and it is the leaves on basil that are the important edible part. A relatively mild water-soluble nitrogen fertilizer applied weekly will help keep you basil productive if you are harvesting leaves regularly.
When flowers appear on your basil plants, pinch them off. This encourages the plant to invest more energy in leaf production and away from production of flowers. To harvest your basil, pinch off a few of the plant's upper leaves at the base. Never remove all of the leaves from a single plant, or you risk killing the plant for the season. Instead, harvest a few leaves from several different individual plants.
Basil does not compete well with weeds when grown outdoors. To help your basil thrive, you'll need to weed around it regularly. You can also mulch around basil to help suppress weeds. If you do mulch, the soil will retain moisture and require less watering.