Sow holy basil seed when the outside temperature is consistently 65-70 degrees Fahrenheit, typically in April and May. Put a thin layer of vermiculite over the seeds to act as a soil conditioner.
When seedlings are large enough to be handled easily, transfer them to slightly larger pots, working up to a 30 cm pot. When transplanting outside, choose an open, sunny space. Holy basil plants grown in containers should be fed with a good plant food every 2 weeks. Water the plants well, allowing the soil to dry between waterings.
Holy basil is susceptible to basil wilt, which causes the plants to wilt and develop a brown color overnight. The disease is transmitted easily and efforts to save the plant will be fruitless. Dispose of the diseased plant, wash containers and garden tools used with it, and thoroughly wash your hands to keep contamination risk to a minimum. Inspect other plants to insure that they are free from aphids and their waste, which can spread the disease.