Blossom End Rot
TreatableNutrient problem · does not spread
Blossom end rot is not a disease and cannot spread. It is a calcium delivery failure: calcium moves through the plant in water, and when watering is erratic the fruit tips — the furthest point from the roots — miss out. Almost all garden soil already has plenty of calcium, which is why adding more usually does nothing.
What it looks like
A flat, sunken, leathery brown-black patch on the bottom of the fruit — the end opposite the stem, where the flower was. It starts as a small water-soaked spot and enlarges. The rest of the fruit looks perfectly healthy.
How to confirm it
- Always at the blossom end, never the stem end, and never on the side.
- Flat and leathery rather than fuzzy or soft.
- Affects the earliest fruit most, and often stops on later trusses.
- Nothing spreads to neighbouring plants.
What to do
- 1Water consistently and deeply. Irregular watering is the actual cause, and fixing it fixes the problem.
- 2Mulch to even out soil moisture.
- 3Remove affected fruit so the plant stops investing in it.
- 4Skip the calcium sprays and eggshells. Foliar calcium does not reach the fruit meaningfully, and the soil almost certainly is not short of it.
What it gets confused with
One observation settles each of these.
Anthracnose lesions are round, sunken and can be anywhere on the fruit, and appear on ripe fruit.
Sunscald appears on the shoulder facing the sun as a pale papery patch, not at the blossom end.
Preventing it next time
- Keep soil evenly moist, especially in containers, which dry out fastest.
- Avoid heavy nitrogen feeding during fruit set — it drives leafy growth that competes for calcium.
- Do not damage roots by cultivating close to the plant.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.