Courgette: dark sunken patch at the bottom of a fruit

What it is likely to be on courgette

1. Blossom end rot

   Candidate 1common on this plant

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Blossom end rot
   • Royal Horticultural Society: Courgettes and marrows — fruit problems

   Checked 2026-08-13

   A dark, sunken, leathery patch at the flower end of a fruit. It is not a disease and nothing is attacking the plant: the fruit could not move enough calcium into its fastest-growing tissue while it was forming, almost always because water supply was irregular.

   Points towards it

   • · a courgette carries an enormous leaf area over a small root system, and an hour of water shortage in a hot week reaches the fruit first
   • · demand outruns supply in exactly the weather when the plant is fruiting fastest
   • · it happens in the ground and in containers, though a container-grown plant is far more prone to it
   • · particular fruit are affected while others on the same plant swell normally

   Argues against it

   • · a courgette in consistently wet ground losing its fruit tips is more likely to have a rot coming in through the dead flower
   • · grey mould on the old flower is a fungus taking the fruit rather than a calcium transport failure

   Check this next

   Ask whether the little courgette got bigger before it went wrong, because that is what separates this from a pollination failure. A fruit affected by blossom end rot swells normally to finger length or beyond and THEN goes brown, dry and leathery at the tip, working back up the fruit. An unpollinated one never swells at all: it stays the size it was at flowering, yellows evenly from the tip and shrivels within days. Cut one across — dry brown firm flesh at the tip is this; a fruit that is simply soft and watery all through is not.

   What to do now

   Water heavily and consistently at the root, and mulch — a courgette in dry ground in July is losing fruit for a reason that a hose fixes within a week. Take the affected fruit off so the plant is not carrying them. Move a container-grown plant into the largest pot you have or into the ground; the fruit tip is the first thing to suffer when eight litres of compost has to support a metre of leaf in a heatwave.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Courgettes and marrows — cultivation
   • Royal Horticultural Society: Blossom end rot — control

   Checked 2026-08-13

2. Grey mould

   Candidate 2very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Grey mould (botrytis)
   • Agriculture and Horticulture Development Board — AHDB: Protected crops — botrytis

   Checked 2026-08-13

   Soft fruit turning brown and collapsing under a fuzzy grey coat, often overnight in wet weather. It is the single biggest cause of strawberry losses in a wet British summer, and it infects at flowering rather than when the mould appears.

   Points towards it

   • · the fungus produces a visible grey-brown fuzz on the dead flower and the rotting fruit tip, which no disorder does
   • · botrytis needs damp still air and a dead flower to enter through, which is what a wet British August provides
   • · a crowded plant in a wet season or an unventilated tunnel both hold the humidity it needs
   • · it takes individual fruit, usually the ones whose flowers stayed attached and wet, rather than the whole plant

   Argues against it

   • · dry air and dry fruit stop it, and a fruit failing in a dry hot spell is failing for the other reason
   • · hot dry weather suppresses botrytis almost completely

   Check this next

   Look at the old flower still attached to the end of the fruit. Grey mould comes in through the dying flower, so the rot starts exactly there and works back into the fruit, and there is a grey-brown fuzz on the flower and on the wet rotting tissue — visible with the naked eye, and unmistakable if you look at it against the light. The fruit is soft and wet rather than dry and leathery, which is the opposite of blossom end rot. It follows wet still weather rather than a hot dry spell.

   What to do now

   Pick off the affected fruit with the flower still on it and bin it rather than composting it, and go over the plant removing every dying flower from the ends of the small fruit while they are still fresh. Then open the plant up: cut out some of the oldest leaves so air moves through the crown, space plants further apart next season, water the soil rather than the plant, and ventilate a tunnel day and night in damp weather. Nothing available to a home grower treats it once it is in the fruit.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Grey mould — control
   • Garden Organic — Garden Organic (Henry Doubleday Research Association): Cucurbits — airflow and watering

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on courgette — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general dark sunken patch at the bottom of a fruit page lists causes across all plants, and the Courgette profile lists the problems it is prone to.