Evening primrose is an attractive herb that grows in mild climate of North American and Europe as well as many other areas of the world with similar climates. However, evening primrose is cultivated and processed primarily in Canada and the United States. Evening primrose oil has been praised for centuries for its healing powers in a wide range of ailments. The secret of the evening primrose is in the seed, which contains the essential fatty acid GLA (Gamma Linolenic Acid). Most of the health benefits of evening primrose oil come from this powerful substance.