Skip to content

Blossom end rot

ProblemsAlso: BER

A dark, sunken patch at the tip of the pod. A calcium problem, but usually caused by irregular watering rather than a lack of calcium in the compost.

A dark, sunken, leathery patch at the blossom end of the pod, the end furthest from the stalk. It shows up while the fruit is still developing and spreads as the pod grows.

It is not a disease

Nothing is infecting the plant. Blossom end rot is a calcium problem inside the fruit, and it does not pass from pod to pod or plant to plant. There is no fungicide for it and nothing to isolate.

It is almost never a shortage of calcium

This is the useful part. British compost and tap water contain plenty of calcium. The trouble is that the calcium is not reaching the fruit, because calcium travels in the plant's water stream, and a plant that swings between bone dry and flooded cannot move it steadily.

So check, in this order:

  1. Watering consistency. Little and often beats a soaking every few days. A pot that dries out at lunchtime and gets drenched at six is the classic cause.
  2. Pot size. A plant in a pot too small for it by July cannot be watered consistently whatever you do. Pot it on.
  3. Feeding. Over-feeding raises the salt concentration around the roots and makes water harder to take up. Feed at the stated rate, onto compost that is already moist.
  4. Root trouble. Anything that has damaged the roots will show up this way, including letting them cook in a black pot in full sun.

Reaching for a calcium supplement is the common response and usually the wrong one. The RHS is blunt about the sprays in particular: calcium is poorly absorbed by fruit and moves badly from leaf to fruit, so a foliar feed does not get calcium to the place that needs it.

The affected pod will not recover

Nothing turns that tissue back. Pick it off so the plant stops feeding it, fix the watering, and later pods come through clean. One marked pod is not a lost crop. The same inconsistency tends to show up earlier in the season as flower drop, so fixing it pays twice.

Chillies get this less often than tomatoes do, which is why almost everything written about it is written about tomatoes. The cause and the fix are the same.