Rising temperatures and changing patters of precipitation could affect the quality of the petals used to make Bulgaria’s renowned rose oil in the coming decades, warns a report published by Bulgarian open knowledge platform Climatheca. 

Bulgaria is one of the top producers of rose oil and other rose products worldwide, alongside Turkey. The best-quality rose oil is produced in the microclimate of the Rose Valley, where the flowers have been cultivated for centuries. 

There are records of roses and rose oil dating back to the Odrysian kingdom, an ancient Thracian state in the 5th-3rd century BC. Rose gardens have been cultivated in the town of Karlovo since 1712. In 1820, the first oil factory was opened in the town of Kazanlak. 

Today, between 2 and 3.5 tonnes of rose oil are produced in Bulgaria every year. This requires the cultivation of thousands of roses; to produce just one gram of rose oil, more than 1,000 rose petals are needed. 

They have to be plucked in the morning between 5.00am and 10.00am, with the essential oil content found to be highest around 7.00am. Harvesting is carried out exclusively by hand. 

They are then used to make rose oil and other products such as rose water, rose potpourri, rose jam, rose tea and even rose brandy. 

The quality of the petals and their oil content is heavily dependent on weather conditions, with the combination of heat and humidity raising the quality of the oil. 

Conversely, low humidity negatively affects the quality of the rose oil, and soil dryness brings down the yield of flowers.

Some changes in the local climate have already been observed, though they are not yet jeopardising the production of rose petals. 

Some of the warmest years since records began have been since 2000. However, there have also been several cooler spring seasons with cold Aprils. Meanwhile, there is no clear trend in precipitation, though there have been signs of an increase in rainfall during the June harvest over the last 10 years. 

Expectations for the next climate period 2021-2050 are for higher average temperatures for all seasons and all regions of Europe and Bulgaria, the report warns. 

“The summer period is expected to show the greatest temperature increases, followed by winter and spring. Warming winters and an increase in temperature during the spring period of between 0.5 and 1.5 °C would have the greatest impact on rose oil quality,” writes the report’s author, Nadezhda Shopova. 

Given the Rose Valley’s microclimate, it should be less affected by general trends than the rest of the country. However, the report says, "climatic pressure can cause a change in the onset of flower set towards an earlier date, and can also affect the duration of flowering. In addition … an increase in temperature can cause a decrease in the essential oils of the petals and the quality and aroma of the rose oil.”

Overall, the average air temperature in the Rose Valley region is predicted to rise by between 1° and 2°C by 2025, while precipitation is expected to fall. Roses may also be affected by extreme events such as drought and waterlogging linked to climate change. 

"The data show that in the more distant future climate pressures may push back the onset of flower set towards an earlier date, and that changing climate conditions may affect the length of the flowering period,” says the report.

“As indirect consequences, the development of diseases and enemies will probably be observed, which would also increase the costs associated with the increase in plant protection activities.” The main threat to the rose is the agrilus beetle, which thrives in warmer winters, as well as diseases such as rust, black leaf spot and powdery mildew.

On the other hand, climate change could enable roses for rose oil to be grown in other parts of Bulgaria, just as fig cultivation now takes place in larger parts of the country, but it is not yet clear if this would be successful. 

In response to the potential threats to rose-growing areas of Bulgaria, a strategy for the development of rose production for the period 2021-2027 has been prepared. It includes, for example, the inclusion of the sector in specialised labour recruitment programmes and government incentives for research and innovation. 

“Despite the climate pressure, Bulgaria has very good chances and opportunities to maintain its leadership position, but the state should have an active role in solving the problems of the sector,” says the report.