Blossom-End Rot: Not a Disease, a Heat-Calcium Crime

Blossom-end rot (BER) looks like a disease: a dark, leathery, sunken spot on the blossom end of tomatoes, peppers, and eggplant. But it isn’t caused by a pathogen. Think of it as a climate-driven “delivery problem”—the fruit can’t get enough calcium at the moment it’s rapidly expanding.

What you’ll see (and when)

BER usually shows up on the first flush of fruit or right after a weather swing.

Common symptoms:

• Small, water-soaked spot at the blossom end that turns brown/black
• Sunken, leathery patch that can invite secondary molds later
• Affected fruit may ripen early and taste off; the plant otherwise looks healthy

Heat and fast growth are frequent triggers. When daytime highs push above 90°F (32°C) for several days—especially with warm nights above 70°F (21°C)—plants transpire differently, and calcium movement to fruit becomes unreliable.

The real culprit: calcium can’t reach the fruit

Calcium isn’t “pumped” into fruit; it moves with water flow. Anything that interrupts steady moisture or shifts water toward leaves instead of fruit can cause BER even if your soil contains plenty of calcium.

Common climate-linked causes:

• Irregular watering (soil swinging from dry to saturated)
• Heat waves and hot winds increasing leaf demand
• Over-fertilizing with nitrogen (lush leaves outcompete fruit)
• Root stress (compaction, waterlogging, root damage)
• High salinity from heavy fertilizer use or salty irrigation water

Confirm it’s BER (not blight)

A quick check:

• BER is almost always on the blossom end, not random spots.
• Leaves typically lack the spotting/yellow halos common with many diseases.
• Multiple fruits on the same plant can be affected after a heat or watering shift.

What to do this week

You can’t “heal” a damaged fruit, but you can protect the next ones.

Action steps:

• Water for consistency: aim for evenly moist soil to a 6–8 inch depth. In hot spells, many containers need watering daily; in-ground beds often need 1–1.5 inches/week, more during heat.
• Mulch 2–3 inches (straw, shredded leaves, bark) to reduce moisture swings.
• Pause heavy nitrogen: avoid high-N feeds during fruit set; choose balanced or lower-N options.
• Protect during heat: use 30–40% shade cloth when highs exceed 90°F (32°C), especially for container tomatoes.
• Pick off badly affected fruits to redirect resources to healthy set.

Should you add calcium?

Only if it’s actually lacking—or unavailable.

• If soil pH is below 6.0, calcium uptake suffers; adjust toward 6.2–6.8.
• If you haven’t limed in years and your soil test shows low calcium, use garden lime (slow) or gypsum (doesn’t raise pH).

Foliar calcium sprays can help marginally, but they won’t replace steady soil moisture. In a warming climate, BER prevention is less about “more calcium” and more about stable water, cooler roots, and gentler growth.