Use fertilizer sparingly on herbs, especially the fast-growing types like basil. Too much fertilizer can reduce the herbs' flavor. Adding organic matter to the soil at the time of planting is often all the "fuel" that herbs need.
Don't Let Them Flower
If you're growing herbs to eat, don't let them flower. The energy a plant spends in blooming and setting seed saps the plant of its potency as a food product. As soon as they appear to be heading to that stage, deadhead them.
Parsley is an easy plant to tuck into containers with other veggies — here, purple kale — and can stand some shade and cool weather.
No Need for Pesticides
Diseases and insects are rarely a problem for garden herbs. Give the plants plenty of light, good drainage and air circulation, and natural predation usually takes care of the rest. Don't use pesticides on herbs.