How do you keep basil from turning brown?

Trim the cut ends, put the bunch in a glass, jar, or vase of water that will fit in the fridge, and cover the whole thing, or at least the basil leaves, with a plastic bag. Put the whole in in a refrigerator. Basil kept that way will stay vibrant and green for up to a week.

Can you use basil after it turns brown?

While the browning may reduce plant yields and produce an unsightly leaf, the basil is good so long as it retains a pleasant fragrance and is not slimy or mildewed. You may want to avoid using brown-spotted basil in dishes for guests or in recipes that benefit from a flawless presentation.