Blossom end rot

Updated June 2026

Worst on early fruit in hot, dry spells through summer, December to February.

Blossom end rot is not a disease but a calcium disorder driven by uneven watering, showing as a sunken black patch on the bottom of tomatoes, capsicums and zucchini. The calcium is usually in the soil but cannot reach the fruit when watering swings between wet and dry, so steady moisture is the fix.

How to identify

• A water-soaked spot at the blossom end of the fruit that turns sunken, brown and leathery
• First and worst on the earliest fruit of the season
• Affected fruit otherwise growing normally above the rot
• More common in pots and beds that dry out between waterings

How to prevent

• Water deeply and evenly, never letting plants swing from bone dry to soaked
• Mulch well to hold steady soil moisture
• Avoid heavy nitrogen feeding, which pushes fast growth that outruns calcium
• Lime acid soils before planting so calcium is available

How to control organically

• Even out your watering, the single most important fix
• Pick off affected fruit so the plant puts its energy into clean fruit
• Mulch and keep moisture steady, especially for plants in pots
• Check and correct soil pH and calcium for the next crop
• Expect later fruit to come good once watering steadies