Rosemary (Rosmarinus officinalis) is a hardy perennial herb known for its aromatic foliage and resilience. However, yellowing leaves can indicate underlying issues affecting the plant's health. From the plant's perspective, this discoloration is often a stress response to environmental or physiological factors.
Rosemary thrives in well-drained soil and is highly susceptible to root rot if overwatered. When roots are waterlogged, oxygen deprivation occurs, impairing nutrient uptake. The plant responds by yellowing leaves, starting from the lower foliage. To resolve this, reduce watering frequency and ensure the soil dries between waterings. Planting in sandy or gritty soil mimics rosemary's native Mediterranean conditions.
Yellowing leaves may signal nutrient imbalances. Nitrogen deficiency, for example, causes older leaves to turn yellow as the plant reallocates nutrients to new growth. Iron or magnesium deficiencies can also lead to chlorosis (yellowing between leaf veins). A balanced, slow-release fertilizer or compost tea can replenish nutrients, but avoid over-fertilizing, as rosemary prefers lean soil.
Rosemary prefers slightly alkaline soil (pH 6.0–7.5). Acidic soils can lock out essential nutrients, triggering yellowing. Test soil pH and amend with lime if needed to restore balance. Container-grown rosemary may require periodic repotting with fresh, pH-adjusted soil.
As a sun-loving plant, rosemary requires at least 6–8 hours of direct sunlight daily. Inadequate light weakens photosynthesis, leading to pale or yellow leaves. Move potted rosemary to a brighter location or prune nearby shading plants in garden beds.
Spider mites, aphids, or fungal infections like powdery mildew can stress rosemary, causing yellow foliage. Inspect leaves for webbing, spots, or insects. Treat infestations with neem oil or insecticidal soap, and improve air circulation to prevent fungal growth.
Rosemary dislikes high humidity or sudden temperature drops. Cold drafts or excessive moisture can trigger leaf yellowing. Protect outdoor plants with mulch in winter and ensure indoor rosemary is away from heaters or cold windows.
Older leaves naturally yellow and drop as part of the plant's growth cycle. If only a few lower leaves are affected, this is likely normal senescence. Prune yellowed foliage to redirect energy to healthy growth.
Newly transplanted rosemary may yellow temporarily as roots adjust. Minimize stress by transplanting in cooler weather, watering thoroughly, and avoiding root disturbance. Recovery typically occurs within a few weeks.
Over-pruning or cutting into woody stems can shock the plant, leading to yellowing. Prune selectively in spring or early summer, focusing on soft green growth to encourage bushiness without stressing the plant.
