The sudden appearance of yellow leaves on blueberry bushes, known as chlorosis, indicates a problem with the plant’s growing environment. Blueberries are members of the Ericaceae family, which thrive in specialized, highly acidic environments. When the bush is denied the unique conditions it requires, its ability to produce chlorophyll is compromised, causing the normally deep green foliage to turn pale yellow. Yellowing leaves are often the first sign that the plant’s fundamental growing environment is incorrect.
The Problem: High Soil pH
The most common reason a blueberry bush turns yellow is incorrect soil pH, which should ideally be maintained between 4.5 and 5.5. When the pH rises above this range, it triggers a chemical reaction that makes micronutrients unavailable to the roots. The plant cannot absorb iron, even if it is abundant in the soil, because the higher pH causes iron molecules to bond tightly with soil particles.
This inability to absorb iron is termed iron deficiency chlorosis. The symptom first appears on the newest growth at the tips of the branches. Affected leaves display a distinct pattern where the tissue between the veins turns bright yellow, while the veins themselves remain dark green. Since iron is an immobile nutrient, older leaves retain their green color longer because they received their supply before the deficiency began.
Identifying Other Nutritional Shortages
Other nutritional issues can also cause leaves to yellow, with symptoms varying based on the nutrient’s mobility. If the plant lacks Nitrogen, a mobile nutrient, yellowing appears first on the older, lower leaves. The plant moves stored Nitrogen from these leaves to support new growth, causing them to turn uniformly pale yellow or sometimes develop a reddish tint before dropping off.
Magnesium deficiency also affects older leaves first. However, it presents a distinct pattern of interveinal yellowing or reddening on mature leaves, sometimes with margins curling or becoming scorched. Observing which leaves are affected first—new growth (iron) or old growth (Nitrogen/Magnesium)—helps narrow down the potential cause before treatment.
When Watering is the Culprit
Problems with water management can induce chlorosis by compromising the root system. Blueberries require consistent moisture but have shallow, fine roots highly susceptible to damage from waterlogged conditions. Excessive watering or poor drainage displaces oxygen in the soil, leading to root suffocation and root rot.
When roots rot, the plant cannot absorb water or nutrients effectively, causing general yellowing and wilting. Conversely, drought stress also inhibits nutrient transport and causes stress-induced yellowing, often alongside dry, brittle leaves. Maintaining a consistently moist, but not saturated, root zone is necessary to ensure root health and efficient nutrient absorption.
Steps to Restore Green Foliage
Diagnosing and correcting chlorosis begins with a professional soil test to measure the pH level. If the pH is too high, the solution involves incorporating elemental sulfur, which slowly lowers the pH over several months as soil bacteria convert it into sulfuric acid. For a faster, temporary fix, a foliar spray of chelated iron can provide the plant with an immediate dose of the micronutrient.
To maintain acidity, only use fertilizers formulated for acid-loving plants, such as those containing Nitrogen in the ammonium form, like ammonium sulfate. If poor drainage is the cause, amend the soil with organic matter like peat moss to improve structure or transplant the bush into a raised bed.