Oregano

Identification and origin

Origanum vulgare belongs to the mint family, Lamiaceae, alongside thyme and mint. Its native range is huge: from the Azores, Madeira and the Canary Islands to North Africa, then across nearly all of Europe, from the British Isles to Scandinavia, and on to Turkey, the Caucasus, Iran, Central Asia, Siberia, the Himalayas, China and Taiwan. The genus name is thought to come from the Greek oros, “mountain,” and ganos, “joy.”

It is a bushy perennial with a woody base and deciduous foliage. A creeping rootstock sends up upright, square, hairy, often purplish stems 8 in – 2.5 ft tall, sometimes 3 ft, and 12 in – 2 ft wide. The opposite, oval, dark green leaves are about 1 in long and give off a strong, thyme-like aroma.

From summer into early fall, tiny tubular, two-lipped flowers in pink, mauve or white open in loose clusters at the stem tips. They attract bees and butterflies.

Don’t confuse it with sweet marjoram (Origanum majorana), which is milder and sweeter, and less cold-hardy. Greek oregano, Origanum vulgare subsp. hirtum, is the standard culinary form, with a sharp, spicy bite; plants of the wild form are often less flavorful, so taste a leaf before you buy. Common cultivars: ‘Aureum’, with golden-yellow foliage; ‘Compactum’, low-growing, with small, strongly aromatic leaves; and ‘Country Cream’, with variegated foliage. Golden and variegated forms appreciate a little shade during the hottest part of the day.

Light

Oregano wants full sun, at least six hours of direct light a day. It tolerates light partial shade, but grows looser and less fragrant there.

Indoors, set it against a south- or west-facing window and turn the pot often. In winter, a grow light running twelve to sixteen hours a day, 6–12 in above the foliage, makes up for the missing light. Long, floppy stems are a sign it needs more light.

Watering

Once established in the ground, oregano tolerates drought; water only young plants during dry spells.

In containers, the mix dries out quickly in hot, sunny weather. Water when it feels dry to the touch, before the plant wilts, then let it dry out slightly. Never leave it waterlogged, and empty the saucer; porous terra-cotta helps.

Indoors, heated air dries the foliage: group pots together or set them on a tray of moist pebbles. A small fan helps prevent diseases caused by stagnant air.

Potting mix

In the garden, oregano is content with average or even poor soil as long as it drains well, ideally neutral to alkaline. In heavy, wet soil its roots rot: choose a raised bed or a container instead.

In containers, allow at least 6 in of width and depth for a young plant, with drainage holes, and use a peat-free, soil-based potting mix with horticultural grit added, up to a quarter of the volume.

Plants in the ground need no fertilizer. A pot that has been in place for more than a year benefits from a little general-purpose granular fertilizer in late spring. Indoors, a weak water-soluble fertilizer every two weeks is plenty: more hurts the flavor.

Temperature

Common oregano is hardy in USDA zones 4a to 8b and survives winters around -4–5 °F in well-drained soil. Its real enemy is winter wet: shelter pots against a wall, out of the rain, and in rainy climates cover plants in the ground with a well-ventilated cloche. Greek oregano, which is less hardy, benefits in cold regions from a straw mulch applied once the ground has frozen. In containers, avoid temperatures below 5 °F.

Indoors, it grows well at 61–70 °F, ideally 64–70 °F by day and 55–61 °F at night, away from heat vents.

Repotting

Plant outdoors in late spring, at the same depth as in the nursery pot, spacing plants 8–12 in apart. A plant raised indoors first needs to be hardened off, getting used to sun and wind gradually.

In containers, repot when roots grow through the drainage hole, ideally in early spring. To harvest through winter, pot up a plant in fall, keep it warm at a sunny window and move it back outside in late spring. After three or four years the clump turns woody: replace it with a young plant.

Pruning

Tip back the stems once they have grown about 6 in to make them branch. Cut back regularly before flowering: blooms slow growth and dull the flavor of the leaves. At the end of winter, remove old, bare stems, and cut back stems that have finished flowering.

Harvesting doubles as pruning. Snip sprigs from spring to fall; flavor peaks just before the flowers open. Leave four to six pairs of leaves on each stem. Dry small bundles by hanging them in a dark, well-ventilated place. Unlike most herbs, oregano is generally best used dried.

Propagation

Seed does not come true to the parent plant: it is better to propagate a plant whose flavor you like.

Cuttings: in late spring or summer, once the leaves are firm, take 3–5 in pieces from young shoots, strip the lower leaves and insert them in a moist, sandy medium.

Layering: in spring or fall, peg a low stem down to the soil. Also pot up stems that have already rooted around the edge of the clump.

Division: in spring, or after flowering in late summer, split the clump into rooted sections.

Seed: in spring, indoors, scatter the seeds on moist seed-starting mix without covering them, since they need light to germinate. At about 68 °F, seedlings appear in one to three weeks. Avoid overwatering to prevent damping off, then move seedlings into 3 in pots.

Common problems

• Plant collapsing: root rot in heavy or overwatered soil, especially in winter.
• Powdery orange, yellow, then black spots: mint rust, a fungal disease.
• Weak stems, faint aroma: too little light, common indoors.
• Dull flavor: plant left to flower, or too much fertilizer.
• Mottled or tunneled leaves: leafhoppers, leaf miners, thrips, spider mites.
• Sticky shoots, chewed leaves: aphids, whiteflies, mint moth caterpillars, cutworms.
• Indoors: fungus gnats (yellow sticky traps) and aphids (trim off infested shoots).

The same symptom can have several causes: look at light, watering, drainage and roots together before acting.

Toxicity

Oregano is considered toxic to dogs, cats and horses: it contains substances that irritate the digestive tract and can cause vomiting and diarrhea, usually mild. Contact a veterinarian if a pet eats some. For people, it is an edible culinary herb, flowers included.