Blossom end rot: why it happens and how to stop it
Last reviewed September 2026 · written from public-domain USDA/NOAA data and Cooperative Extension references — see how we source data
Blossom end rot is one of the most common problems on home-grown tomatoes, peppers and squash, and one of the most misunderstood — the usual advice to simply add calcium to the soil rarely fixes it.
What it looks like
A flat, dark, leathery patch develops on the bottom (blossom end) of the fruit, typically early in the fruiting season on tomatoes, peppers and summer squash.
It is not a disease
Nothing is infecting the fruit. Blossom end rot is a calcium-delivery problem — the developing fruit is not getting enough calcium to its cells as it grows, even in soil that has plenty of calcium in it.
The real cause: inconsistent water
Calcium moves through the plant dissolved in water, pulled along by transpiration. A dry week followed by a heavy watering interrupts that flow to the fruit far more often, in practice, than a genuine calcium shortage in the soil does.
How blossom-end rot happens - and how to break the chain
Things that make it worse
Anything that interrupts the roots' uptake of water: digging close to plants and cutting roots, waterlogged soil, heavy doses of high-nitrogen or high-salt fertilizer, and very fast growth during a hot spell.
Plants in containers are especially prone because the mix swings quickly between dry and wet. Some varieties - many paste and plum tomatoes, and some peppers - are more susceptible than others.
Preventing it
Water consistently — mulch and drip irrigation both make that a lot easier. Avoid heavy nitrogen feeding early on, which pushes leafy growth faster than the roots that need to keep pace with it. Expect it to fade as watering settles into a rhythm through the season.
Should you add calcium?
Only if a soil test shows low calcium or acidic soil. In that case garden lime raises the pH and adds calcium, but it works slowly, so apply it well before planting.
Calcium sprays on the leaves do little, because calcium barely moves from leaves into fruit. Crushed eggshells break down far too slowly to help this season.
What to do with affected fruit
Pick off fruit with blossom-end rot as soon as you see it, so the plant puts its energy into healthy fruit. The unaffected part of a tomato is safe to eat once the damaged patch is cut away, as long as no mold has set in.
Common questions
Can you eat tomatoes with blossom-end rot?
Yes. Cut away the dark patch and a little around it; the rest of the fruit is fine to eat. Discard fruit that has gone moldy or soft from secondary rot.
Do eggshells prevent blossom-end rot?
Not in any useful way. Eggshells take a long time to break down, and the problem is usually water supply rather than a lack of calcium in the soil. Steady watering and mulch do far more.
Why do only the first tomatoes get blossom-end rot?
The first fruits often set while plants are growing fast and watering is still uneven. As the plant's root system grows and watering settles into a rhythm, later fruit is usually unaffected.
Does blossom-end rot affect peppers and squash?
Yes. Peppers, summer squash, watermelons and eggplant can all get it for the same reason. On peppers it often shows as a pale, sunken patch on the side near the tip.