Greek oregano is the intensely aromatic subspecies used in Mediterranean cooking, far more pungent than common oregano, whose flavour is often faint. The difference is the density of essential oils, which concentrates in full sun and lean soil; rich, moist conditions produce lush but flavourless leaves. It grows 12 to 18 inches and flowers white in midsummer.
Plant it 12 to 18 inches apart in poor to average soil that drains sharply, in full sun, and water only until it is established; wet feet in winter are what kill it. Harvest just before and during flowering, when the oil content is highest, cutting whole stems and stripping the leaves. Dry it by hanging bundles upside down in a dark, airy place; oregano dries better than almost any other herb and the flavour strengthens.
It is reliably perennial in zones 5 to 10. Cut it back hard in early spring to 2 or 3 inches above the base to encourage fresh growth, and divide it every three or four years when the centre goes woody. The flowers are covered in bees and small butterflies, and deer and rabbits leave the whole plant alone. Buy it as a plant from a nursery that grows the true hirtum; seed sold as oregano is often the bland species.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Spider Mites
Tetranychus urticae →Fine stippling or bronzing on leaves, faint webbing on undersides, foliage drying out during hot, dry weather.
Spray foliage with a strong jet of water to dislodge mites. Apply insecticidal soap or horticultural oil to leaf undersides; repeat every 5–7 days as needed.