Thai Basil seeds in garden in full sun when frost danger is over and ground is warm. Make shallow furrows and cover the herb seeds 1/4 inch with loose soil. Keep moist until germination. Basil seeds take between eight and 14 days to germinate and emerge from the soil. After germination, look for the first set of true leaves two to three weeks later. Then, two to three weeks after the first set of true leaves emerge, basil plants should be about 6 inches tall and ready to plant out in the garden.