Blossom end rot (BER) is a physiological disorder impacting many popular garden vegetables, including tomatoes, peppers, squash, and eggplant, causing damage that ruins the harvest. It is not caused by a pest, fungus, or bacterial disease, but rather a disruption in the plant’s nutrient delivery system. Understanding the cause and implementing specific management techniques offers the most effective path to a successful crop. Solving this issue requires immediate action paired with long-term adjustments to the growing environment.
Identifying Blossom End Rot Symptoms
Blossom end rot manifests as a distinct visual symptom solely on the developing fruit. The first sign is typically a small, water-soaked spot that appears on the blossom end of the fruit, the part farthest from the stem. This damage can occur on both green and ripening fruit, often when they reach about half their mature size.
The initial spot quickly enlarges and darkens, turning a characteristic brown or black color. The affected tissue then desiccates, becoming sunken and leathery in texture. While the rot itself is not caused by a pathogen, secondary fungi and bacteria may colonize the dead tissue, sometimes causing a soft or fuzzy-like black growth. The rest of the plant remains completely unaffected by this disorder.
Understanding the Root Cause
Blossom end rot is the result of a localized deficiency of calcium within the developing fruit. Calcium is an essential macronutrient required for the formation of cell walls, providing structural integrity to plant tissues. When calcium delivery fails, the cell walls at the fruit’s tip collapse, leading to the sunken, necrotic tissue.
The problem is rarely due to a genuine lack of calcium in the soil, which often contains sufficient amounts. Instead, BER occurs because the plant cannot efficiently uptake and transport the available calcium. Calcium is considered an immobile nutrient and moves almost exclusively through the xylem, traveling with the water flow generated by transpiration.
Inconsistent soil moisture—fluctuations between drought and overwatering—is the primary factor that disrupts this water-dependent transport system. Rapid vegetative growth, often spurred by excessive nitrogen fertilization, can also create a sudden, high demand for calcium that the roots cannot meet. Extremes in soil pH, either too high or below 5.5, can chemically bind calcium, reducing its availability for root uptake.
Immediate Steps to Treat Affected Plants
Once the spot appears on a fruit, the damage is irreversible because calcium cannot be redistributed from other parts of the plant. The first step is to remove all currently affected fruit and discard them. Allowing damaged fruit to remain diverts the plant’s limited resources away from healthy, newly-forming fruit.
Immediately stabilizing the soil moisture is the most effective short-term cure to save the remaining crop. Apply a gentle, deep watering to the base of the plant to re-establish a consistent water flow. Consistent watering immediately addresses the primary cause of the transport failure.
Some gardeners use a foliar calcium spray as a temporary measure to quickly boost calcium delivery to the leaves and new growth. While sprays may provide a rapid, localized supplement, they are not a permanent solution because the calcium primarily remains in the leaves and does not easily move into the fruit. This method supports the plant until proper soil and water management can be established.
Preventing Recurrence Through Soil and Water Management
Long-term prevention focuses on creating a stable root environment that supports consistent calcium uptake. Establishing a deep, regular watering schedule is paramount, aiming for approximately one to one-and-a-half inches of water per week, adjusting for weather conditions. The goal is to avoid the moisture shifts that interrupt the steady flow of calcium to the developing fruit.
Applying a thick layer of organic mulch, such as straw or shredded leaves, around the base of the plant helps regulate soil temperature and conserve moisture. Mulching significantly reduces evaporation, preventing the soil from drying out too quickly between watering events. This practice is beneficial for plants grown in containers, which are highly susceptible to rapid moisture loss.
Fertilization practices must be carefully managed to prevent recurrence. Avoid using excessive nitrogen fertilizers, particularly those high in the ammonium form, as this promotes rapid foliage growth and can interfere with the uptake of calcium. A soil test provides specific recommendations for nutrient levels and pH, which should be maintained between 6.5 and 7.0 for optimal calcium availability. If a test confirms low soil calcium, amendments like agricultural lime (for low pH soils) or gypsum (for balanced pH soils) can be added to the topsoil to ensure a permanent supply of the nutrient.