Keep herb plants in pots, lightly watered, in a sunny spot and pick off what you need when you need it. Do not over-water. Buy small plants and plant out in pots, a window box or small patch in the garden. Treat cut herbs like flowers: trim the ends of the stalks and put into a jar of water. They will keep for as long as a bunch of flowers. Coriander does not keep well, however, so if you want it to make a coriander butter, for example, make it the day you buy the coriander and store it in the fridge.