Origanum hortensis Marjoram has a subtler flavor than the similar herb, oregano. It's also beautiful, with gray-green leaves and spikes of tiny white or pale pink flowers. Choose a site that gets full sun. Pick leaves as soon as they're large enough to use; flavor is best before the flowers open. Plant coriander nearby to ward off aphids. Sow seeds directly into the ground after the last frost or start seeds indoors six weeks before the last expected frost. Grow marjoram in pots if you live in a area colder than USDA zone 9. When the weather is mild, keep the plants on a sunny terrace or deck; when temperatures dip toward the frost level, move them to a cool but sunny greenhouse, cold frame or windowsill.