Water basil plants with tepid water to encourage the most vigorous growth.
Water basil plants around the base of the plant. Do not water the leaves.
Ensure that your basil plants receive approximately 1 1/2 inches of water per week. This can be supplied by you or by natural rainfall.
Check the surrounding soil regularly. Soil consistency will vary depending on temperature and humidity. The soil surrounding your basil plant should be moist at all times.
Provide proper drainage. Plant basil in well-irrigated ground that does not tend to collect water and become soggy. Young basil plants, especially, are prone to fungal disease if exposed to standing water.
Consider installing a drip irrigation system. Recommended by the Utah State University Cooperative Extension, drip irrigation systems work well in helping to maintain healthy basil plants.
Grow indoor basil plants in a pot with holes in the bottom that drain into a saucer.
Check the soil every day. The soil should remain moist, but not soggy. Do not allow the soil to dry out.
Water your basil plant until water begins to drain into the saucer. Stop watering, allow the water to complete the draining process, then immediately empty the saucer.