This kind of weather prolongs the flowering period, suppresses oil evaporation, at the same time increasing the yield of oil and producing oil of good quality. A longer flowering period means a longer harvesting campaign at a lower daily output of flowering roses. Such conditions ensure good yield of oil. The mean monthly precipitation in May and June is usually between 80 and 100 liters per square meter. Cloudiness is of such a character that high air humidity is sustained.
Daily temperatures are relatively high and the nights are cool.
Dew is often formed and is welcomed by rose growers, as it is a sign of high yields of attar. The frequent rainfalls and cloudiness during the flowering period are among the main beneficial factors for obtaining larger quantities of essential oil and one of better quality. The absence of intensive sunshine prevents undesired liberation of the volatile aromatic ingredients from the flowers. The wax film is thin, yet the plant does not strive to make it thicker to protect itself from strong solar radiation, as do roses in Iran and elsewhere. This explains the smaller content of stearoptene in the Bulgarian rose oil.