Lavender (Lavandula) is cherished for its fragrant foliage and purple blooms, yet when its silvery-green leaves begin to turn yellow, it is a clear sign the plant is experiencing stress. This discoloration, known as chlorosis, indicates that the plant is not producing enough chlorophyll, the pigment necessary for photosynthesis. Identifying the source requires looking at three main areas: incorrect water management, insufficient light, or an imbalance in the soil’s chemistry.
The Primary Culprit: Hydration and Drainage
The most frequent cause of yellowing is providing too much water or planting in soil that retains moisture for too long. Lavender evolved in arid, rocky conditions, meaning its root system is adapted to dry conditions and requires excellent aeration. When soil remains saturated, roots are deprived of oxygen, quickly leading to root rot.
Root rot is a destructive condition facilitated by opportunistic soil fungi. The infection causes roots to become mushy, blackened, and incapable of absorbing water or nutrients. An overwatered plant typically displays soft, droopy yellow leaves, often starting at the bottom, sometimes accompanied by a foul odor from the soil.
Under-watering can also cause yellowing, but symptoms present differently. A plant suffering from drought stress will shed leaves to conserve moisture, and the yellowing leaves will feel dry and crispy rather than soft and limp. Lavender should only be watered deeply once the top inch or two of soil has completely dried out, preventing the prolonged wetness that triggers root rot.
Light and Environmental Stressors
Lavender is a sun-loving species, and inadequate light is a common factor. The plant requires a minimum of six hours of direct, unfiltered sunlight daily, with eight to ten hours being optimal. When light levels are too low, the plant struggles to photosynthesize efficiently, and leaves turn pale or yellow as chlorophyll production is reduced.
Insufficient light also causes the plant to stretch its stems in an attempt to reach a light source, resulting in weak, spindly growth. This reduced vigor makes the plant more susceptible to issues, including fungal diseases. Lavender also dislikes high humidity, which is often exacerbated by poor air circulation and shade.
High humidity encourages fungal diseases like Botrytis or Septoria leaf spot, which manifest as yellowing or spotting on the leaves. Sudden or prolonged temperature extremes can also induce stress. A cold snap or intense, prolonged heat without proper moisture management can shock the plant, causing the foliage to yellow and drop.
Nutritional Deficiencies and Soil pH
The chemistry of the soil plays a significant role in lavender’s health. Lavender prefers lean, low-fertility conditions and a soil pH that is neutral to slightly alkaline, ideally ranging from 6.5 to 7.5. Growing lavender in rich, acidic soil or over-fertilizing can lead to nutrient-related yellowing.
Applying high-nitrogen fertilizers is detrimental, promoting lush, soft vegetative growth at the expense of flowers and fragrance. This over-abundance of nitrogen can also trigger deficiencies in other elements. For instance, a deficiency in iron or magnesium causes chlorosis where the leaves turn yellow while the veins remain distinctly green (interveinal chlorosis).
An overly acidic soil (pH below 6.5) can chemically lock up essential micronutrients like iron, making them unavailable for the roots to absorb. Since the roots cannot acquire the necessary elements to produce chlorophyll, the plant exhibits nutrient deficiency symptoms and turns yellow. Testing the soil’s pH is the only reliable way to confirm this specific cause.
Action Plan for Recovery and Prevention
Addressing yellowing requires immediate action based on the plant’s symptoms. If the leaves are soft and the soil is wet, the first step is to cease all watering to allow the soil to dry out completely. For potted plants, gently unpot the lavender to inspect the roots. Prune away any black, mushy, or foul-smelling sections with sterilized tools, and repot with fresh, gritty soil.
Prevention includes ensuring the planting location receives at least six hours of direct sun exposure daily. For in-ground planting, heavy clay soil should be amended with coarse sand, grit, or fine gravel to ensure rapid drainage and prevent water retention.
The correct soil pH is maintained by adding amendments like dolomitic lime to raise the pH if a soil test confirms overly acidic conditions. Instead of regular fertilizer, consider a one-time spring application of a low-nitrogen, high-phosphorus supplement like bone meal to support root development. Establish a strict watering schedule, using the finger test to confirm the soil is dry before watering again.