Basil and peppermint both grow in any type of soil as long as it is well-drained. Full sun is needed, although peppermint might need a little afternoon shade in hot temperatures. Neither of these herbs tolerates freezing temperatures. Basil must be planted every year in the spring, while peppermint keeps coming back year after year. Both herbs require at least 1 inch of rainfall or supplemental water per week, but basil is more susceptible to moisture stress.
Start basil by seed by planting 1/2 inch apart in seed trays. Cover with a sprinkling of moistened soil, continue to moisten soil when it gets dry keeping temperatures around 70 degrees Fahrenheit. Germination will occur in five to seven days. Repot in 2-inch pots once seedlings produce two leaves.
Peppermint does produce seed, but it rarely germinates. Purchase plants from a nursery or obtain a root division from a friend.
Plant basil and peppermint outside when temperatures stay 60 degrees or more. Space basil plants 12 inches apart in rows 2 feet apart or plant four in a 10- to 12-inch pot. Basil does not spread, but peppermint does by underground runners, and it must be contained so it does not choke out basil and everything in the garden. Plant peppermint in pots above-ground, or sink the pot in the ground so the lip is 3 inches above the soil line.
Keep the herbs evenly moist and place mulch around the bottoms to discourage weed growth and maintain moisture. Pinch off flowers to keep leaf production at a maximum. Pinch back tops of basil branches to encourage bushy plants. Peppermint grows readily without pinching. Neither plant needs fertilization, in fact, too much fertilizer causes basil to lose flavor.
Prune basil every three or four weeks by cutting back each branch right above a leaf node, leaving at least four leaves on the branch. Tie the stems together and hang to air dry or place in a microwave enveloped in paper towels at one-minute intervals until dry.
Harvest peppermint once it reaches 10 inches tall, and hang to air-dry.