Blossom end rot is a physiological disorder that mostly affects tomatoes but can also affect cucumbers, peppers, squash and aubergines. The tell-tale sign is dark blotches on the bottom of the fruits.
Look for a circular patch, greenish brown to black measuring 1cm to 2,5cms.
Lack of calcium in the fruit leads to swelling of the cells and a reduction in the number of new cells.There is usually sufficient calcium in the soil, so the problem is more likely to be that the calcium isn’t reaching some parts of the plant.
High humidity, erratic watering, cold soil, root damage, high temperatures and fluctuations in temperature can all make it difficult for the plant to transport calcium from the soil to all parts of the plant.
You can’t save the individual fruit once they have rot, but you can prevent more fruit developing the disorder.
1) Water evenly – don’t let the soil dry out too much and water twice a day rather than giving a thorough soaking once per day.
2) Manage humidity – open your greenhouse or polytunnel doors on hot doors.
3) Manage temperatures – consider using a fan, netting or greenhouse shading to reduce the intensity of sunlight and temperature of your greenhouse or polytunnel.
4) Don’t let the soil get cold - at night, if temperatures are below 4°C use a greenhouse heater and if growing outdoors bring the plants inside.
5) Remember - that a plant with a healthy start in life will be better able to withstand stress in later life, so select the strongest seedlings for potting-on, provide seedlings and young plants with sufficient heat and light so that the roots are strong and healthy.