Marjoram is a tender perennial in the mint family, closely related to oregano but milder and sweeter. In upstate New York it is grown as an annual or overwintered indoors, since it does not survive Zone 6b winters outdoors. Gardeners grow it for fresh and dried culinary use; the flavor is strongest just before flowering.
Marjoram needs warmth and full sun to develop good flavor. It germinates slowly and is sensitive to cold, so start seed indoors and transplant only after the soil has warmed. Pinch growing tips regularly to keep plants bushy and to delay flowering, which preserves leaf quality. Harvest leaves in the morning before heat reduces the oils.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
Thyme Root Rot
Stems blacken at the base, foliage yellows and wilts, and roots turn brown and mushy. Common in heavy or poorly drained soil.
Remove affected plants and avoid replanting thyme in the same spot. Improve drainage with grit or raised beds, and water only when soil is dry.
Spider Mites
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.
Aphids
Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.
Botrytis (grey mould)
Grey fuzzy mould on petals and stems, worst in cool wet conditions.
Remove affected parts immediately. Improve air circulation. Avoid overhead watering. Apply copper fungicide if severe.