Yes I was waiting for the day when I can pick my first sweet pepper and within a few days look what happened to my precious fruit. The plant is big and healthy but I was very silly and kept the greenhouse door shut for days because of the cold weather and the humidity was about 100% in there; my big mistake. Blossom end rot is a fruit disorder of tomatoes, aubergines and peppers. This non parasitic damage can be very serious at times and but if you take action after the first occurence you will have some harvest a bit later in the season, as the blossom end rot normally appears on the first fruits.
The most common symptom is a small watery rotting spot on the blossom end of the fruit just when the fruits begin to mature. It can appear at earlier stages too while the fruits are still small and green. As the disorder develops it becomes larger and leathery and in dark brown to black in colour. Half of the fruit can become rotten in a few days. On the rotting fruits usually some pathogens (bacteria or fungi) will appear too, destroying the fruits completely. Secondary molds often colonize the affected area, resulting in a dark brown or black appearance. Blossom end rot can also appear on the side of the peppers, but on tomatoes it is normally right in the middle.
Why it appears?
Blossom end rot is not parasitic (not fungi or bacteria) but it is associated with a low-level of calcium in the fruits. The disorder develops when a fast growing fruit does not get enough calcium to support its cellular growth. When the fruit becomes deprived of calcium the cells will break down and start rotting. The food comes through the stalks to the fruit so it is obvious that the lower (blossom end) part of the fruit will develop this disorder. The lack of calcium in the soil and other factors too will increase the risk of blossom end rot. Other factors like excessive water level fluctuations, rapid plant growth due to high level of nitrogen fertilization, high humidity and lots of magnesium in the soil will also help developing this stress disorder.
Soil ph around 6.5 will ensure an optimum calcium level in the soil, use some lime to achieve this 3-4 months before planting. Ensure steady plant growth and avoid over fertilization especially after the first fruit set. Keep the soil moisture level constant, and avoid overwatering and drought stress. Open the greenhouse doors and windows even in cooler days to avoid condensation and high humidity.