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Blossom end rot
EnvironmentalMedium impact
A calcium deficiency disorder causing dark, sunken, leathery patches at the blossom end of developing fruit. The root cause is almost always irregular watering rather than calcium-poor soil - drought stress prevents calcium uptake even when soil levels are adequate.
Currently in peak season - extra vigilance worthwhile.
Key facts
- Type
- Environmental
- Active season
- Jun - Sep
- Peak season
- Jul - Aug
- Vulnerable stages
- Fruiting · Growing · Harvesting
- If confirmed
- Act soon
Signs & symptoms
- -dark brown or black, sunken, leathery patch at the base (blossom end) of fruit
- -on tomato: first and second truss fruits most commonly affected
- -affected tissue is dry and firm, not soft or mouldy
- -plant otherwise looks healthy
Management
Do now
- -Water consistently and deeply - avoid allowing compost or soil to dry out between waterings
- -Remove affected fruits to allow the plant to redirect energy to healthy ones
- -Check that containers are not drying out rapidly in hot weather
Prevention
- -Mulching around plants helps retain soil moisture and reduces fluctuation
- -Use a consistent watering regime from fruit set onwards - erratic watering is the primary trigger
- -Avoid high-nitrogen feeding which promotes rapid leafy growth at the expense of calcium uptake
Further reading
- -Calcium deficiency in blossom end rot is almost never due to lack of calcium in the soil - it is caused by inability to move calcium to developing fruit due to water stress interrupting the transpiration stream
- -Inconsistent watering (wet-dry-wet cycles) is the key trigger; maintaining even moisture is the cure