Tomato Blossom End Rot: Complete Guide

Why it happens: Calcium is transported through plants via water in the xylem vessels, moving from roots to leaves and fruit. When watering is irregular - alternating between drought stress and heavy watering - this transport system is disrupted. During dry periods, calcium movement slows or stops entirely. Even brief water stress during the critical period when fruit cells are rapidly dividing can cause permanent damage that manifests as BER days or weeks later.

Signs this is your problem: Soil frequently swings from very dry (cracked surface, wilting plants) to saturated after watering. Plants wilt noticeably between waterings or during hot afternoons. BER appears after periods of drought or heat waves. Container-grown tomatoes are especially affected because pots dry out quickly. For proper watering techniques, see our watering guide.

Solution: Establish consistent, deep watering practices. Provide 1-2 inches of water per week through drip irrigation or soaker hoses rather than overhead sprinklers. Water deeply 2-3 times per week rather than shallow daily watering - this encourages deep root growth that makes plants more drought-resistant. Check soil moisture regularly by inserting your finger 2-3 inches into the soil; it should feel consistently moist but not waterlogged.

Why it happens: Even when soil contains adequate calcium, several factors can prevent plants from absorbing it effectively. Soil pH outside the optimal range (6.2-6.8 for tomatoes) makes calcium chemically unavailable. Competition from other nutrients - particularly excess nitrogen, potassium, or magnesium - can block calcium uptake at the root level. Damaged or underdeveloped root systems simply cannot absorb enough calcium to meet the demands of rapidly growing fruit.

Signs this is your problem: Young, rapidly growing fruit is affected first while older fruit may be fine. Leaf tips may show browning or curling (calcium deficiency symptoms in foliage). You've been fertilizing heavily, especially with high-nitrogen formulas. Soil hasn't been tested recently and pH is unknown. Plants were recently transplanted or had root disturbance.

Solution: Test your soil pH and adjust if necessary - add lime to raise pH if soil is too acidic (below 6.2). Use balanced fertilizers rather than high-nitrogen formulas that stimulate excessive vegetative growth. Add gypsum (calcium sulfate) to provide calcium without affecting soil pH, or use bone meal for a slower-release calcium source. Avoid disturbing roots when cultivating around plants. For container plants, use quality potting mix with added lime. Learn more in our soil mix guide.

Why it happens: Rapid temperature fluctuations, extreme heat, high humidity, and damaged root systems all stress plants and disrupt the delicate process of calcium transport. Heat causes plants to transpire rapidly, pulling water and calcium preferentially to leaves rather than fruit. Temperature swings cause uneven growth rates that outpace calcium delivery. Container plants are particularly vulnerable because pot temperatures can swing dramatically, cooking roots in black plastic containers or causing rapid moisture loss.

Signs this is your problem: BER appears during or shortly after heat waves (several days above 90°F). Problems are worse in containers than in ground plantings, especially in dark-colored pots. BER occurred after transplanting or root disturbance. Plants are in exposed locations with no afternoon shade protection.

Solution: Apply 2-3 inches of organic mulch (straw, shredded leaves, grass clippings) around plants to moderate soil temperature and retain moisture. Provide light afternoon shade during extreme heat using shade cloth or strategic placement near taller plants. Be extremely gentle when cultivating to avoid damaging shallow feeder roots. For containers, use light-colored pots at least 5 gallons in size, consider double-potting (placing the grow container inside a larger decorative pot) for insulation, and move pots to afternoon shade during heat waves.

Why it happens: Excessive nitrogen fertilization is a common culprit in blossom end rot cases. High nitrogen levels stimulate rapid vegetative growth - lots of lush green foliage - at the expense of fruit development. This fast-growing tissue demands more calcium than the plant can supply, especially if water uptake is inconsistent. Additionally, excess nitrogen, potassium, and magnesium compete with calcium for uptake sites in the root system, effectively blocking calcium absorption even when soil levels are adequate.

Signs this is your problem: Plants have exceptionally lush, dark green foliage with vigorous vegetative growth. Lots of flowers but poor fruit set or small fruit. Soil has a white crusty appearance (salt buildup from fertilizer). You've been fertilizing frequently or using high-nitrogen formulas designed for lawns or leafy vegetables.

Solution: Switch to balanced fertilizers with lower nitrogen content - look for formulas like 10-10-10 or 5-10-10 where the first number (nitrogen) isn't dramatically higher than the others. Follow package directions carefully and resist the temptation to add extra - more fertilizer does not mean more or better fruit. Consider organic slow-release fertilizers like compost or well-rotted manure that release nutrients gradually. If you suspect salt buildup, flush containers with plain water to leach excess salts from the soil.