The International Herb Association has designated the genus Origanum the Herb of the Year 2005. Oregano and marjoram are common names for different species within this genus, and there are several species in this genus in the mint family (Lamiaceae). There is some confusion about the names for the various species; the European O. vulgare may be called Common Oregano, Wild Marjoram, or Pot Marjoram depending on where you live; this plant has relatively little flavor. O. onites, from Greece and Crete, may also be called Pot Marjoram or Greek or Cretan Oregano. Also known as Greek Oregano is O. heracleoticum (also called O. vulgare subsp. hirtum, O. hirtum, or O. vulgare prismaticum), from Italy, the Balkan Peninsula, and West Asia, which is less hardy than O. vulgare, but is much more flavorful. Another complication is that different types of oregano readily hybridize. But in all of these plants, essential oils, particularly carvacrol, provide the distinctive oregano flavor. Sweet marjoram, O. majorana from Asia Minor, is not winter hardy here and has a subtle taste unlike oregano at all because it contains less carvacrol. Italian oregano (O. x majoricum) has a bit of the sweet, perfumey scent of marjoram.
Several other unrelated plants with high amounts of carvacrol also have local common names of oregano. “Mexican oregano” usually refers to a tall, tender plant in the verbena family (Verbenaceae), Lippia graveolens, that has a similar, but stronger oregano flavor, but may also refer to Poliomintha longiflora and Plectranthus amboinicus (syn. Coleus aromaticus) in different parts of Mexico. P. anboinicus is marketed as oregano in Puerto Rico, and Cuban oregano or Spanish Thyme in other places. This Caribbean native is a large and thick-leafed plant that resembles a succulent. In Spain Thymus nummularius is sold and used in place of oregano.
Most plants in the genus Origanum are small perennial subshrubs or tender perennials native to the Mediterranean and adjacent areas. In Wisconsin many of the species are not completely hardy and are better grown as annuals or pot plants. O. vulgare has naturalized in the eastern United States. Oregano plants develop woody stems and can grow up to about 30″ tall and wide under optimal conditions, but most types remain at 8-12″ high. Because of its more compact habit, marjoram is often used in English knot gardens.
The leaves of Origanums are oval to spade shaped, dark green, and many are somewhat fuzzy. Marjoram tends to be a more gray green color than oregano, and the leaves are generally smaller and less fuzzy. The composition of the oils, and therefore the flavor, of all of these plants is greatly influenced by climate, moisture levels and soil. Flowers appear on long stalks in summer and will last well into the fall. Oregano typically has pink flowers, while marjoram usually has white blooms.
At least one species of Origanum is used solely as an ornamental. Hopflower Oregano (O. libanoticum) is a vigorous, trailing herb hardy to zone 4b. It can grow 10-15″ tall and spread 18-24 inches. It produces hop-like bracts of lavender and chartreuse through the summer months; in autumn they turn brown and dry. This plant looks best when cascading over a raised bed, rock garden or container. Just like its culinary brethren, hopflower oregano needs well-drained soil in full sun to thrive.
Greek oregano is among the more common oreganos available in the U.S., having ‘true’ oregano flavor. It grows low to the ground, rooting as it grows outward. It is a vigorous spreader, but not invasive. There are numerous named oreganos offered for sale, but because of the confusion among names, it is not always clear what plant you are really getting. Some varieties that are offered include:
- Origanum ‘Herrenhausen’ has reddish-violet flowers.
- Origanum ‘Hopley’s Purple’ has pungent, reddish leaves that can be used either fresh or dried, but is used mainly as an ornamental.
- Origanum ‘Santa Cruz’ is an good choice for pots and planters.
- O. vulgare ‘Compacta’ doesn’t get as large as other types of oregano, but still produces quantities of dark green, fragrant foliage.
O. vulgaris ‘Aureum’ is a golden-leafed, ground cover type used primarily as a landscape plant, such as for edging paths or garden beds. It is edible with mild flavor.
Plants can be started from seeds, cuttings, or crown divisions. The very small seeds are very small and should be started indoors. Barely cover the seeds with a thin layer of sand or fine soil; they germinate better in light. Seeds should germinate in 4-14 days, depending on temperature and light conditions. Transplanted hardened-off seedlings to a permanent location when 2 to 3 inches high and when the temperatures are expected to remain above 45°F. Space plants 12-15″ apart in rows 18″ wide.
However, “oregano” is quite variable when grown from seed (partly owing to the confusion of names, but also to natural variation in carvacrol concentrations in individual plants), so you may prefer to purchase a plant from a reputable dealer. If you have a plant you like the smell or taste of, you can propagate it by taking cuttings or root divisions in the spring.
Oregano grows best in well-drained soil in full sun, while marjoram prefers moister soil but still in bright light. As with most herbs, average to poor soils produce the most concentrated flavors.
Pinch back any flower buds to keep the plants from getting rangy and going to seed. Fertilize yearly with a balanced plant food. You may wish to mulch plants to keep the foliage clean, but in our moist climate this invites root rot. Oregano has few pests, but can become infested with spider mites or aphids.
You can start using the leaves, a few sprigs at a time, once the shoots reach 4-5″ tall until the first frost (if outdoors) or all year long, if in pots inside. Essential oil levels are highest just before the plant blooms, so the best time to harvest is just before flowers begin to develop.
To harvest the entire plant, cut the stems down to the lowest two sets of leaves; the plant should leaf out again within two weeks. Tie in bunches and hang in a warm, dry, shaded place to dry. Once crisp, strip the leaves from the stems and store in an airtight container.
Dried oregano leaves often are more flavorful than the fresh, because the essential oils are more concentrated. Use twice the amount of the fresh herb as you would the dried. But marjoram tends to be better when used fresh.
The leaves of oregano and marjoram are used for flavoring foods, and are best added to hot dishes at the end of cooking to preserve the flavor and prevent bitterness. They are an important component of commercially-produced poultry-seasoning mixes.
Oregano is an essential flavoring in Italian cuisine, where its robust, pungent flavor is great in tomato sauces, on vegetables and grilled meats, and, of course, pizza. Other Mediterranean cuisines use less oregano, but it is of some importance for Spanish, North African and Greek cooking.
Marjoram is more often used in recipes of French or English origin. Its sweeter, milder flavor works in cheese, tomato, bean and egg dishes, salad dressings, seafood sauces, and on poultry.
Oregano also has some medicinal and cosmetic uses, such as in bath oils and sachets to help relieve aches and stiff joints. The dried flowers are used for fragrance in potpourris and perfumes.
– Susan Mahr, University of Wisconsin – Madison
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