Part 2: Harvesting—Seasons and Time of Day

Each of the four seasons is defined by its unique weather conditions. Throughout the seasons, temperatures range from below freezing to swelteringly hot. Precipitation may range from bounteous rainfall to heavy snowfall to none at all in times of extreme drought. Besides temperature and precipitation, the seasons also affect insect presence, soil condition, amount of sunlight, and sunlight intensity.

Perhaps no living creature is more influenced by the seasons than plants—organisms that are unable to seek cover from a storm, scout out extra water, or regulate their temperature. The fluctuating environment produced from season to season widely determines a plant’s ability or necessity to make essential oils. Each plant is unique and will thrive in different environmental circumstances. For instance, fennel thrives in mid-autumn, eucalyptus and lavender in the summer, pine in the early spring, and fir in the heart of winter. It is important that farmers and harvesters are aware of the optimal conditions for each individual plant species. Doing so ensures that the plant material will be harvested when the essential oil yield is highest.

A plant’s essential oil production is similarly affected by the time of day. Jasmine essential oil is just one example of a plant with very specific harvesting requirements on a day-to-day basis. It is important to recognize when the yield of jasmine flowers will be highest because jasmine oil is among the most rare and precious oils on the market today. The flowers of the jasmine plant produce a beautifully fragrant essential oil; however, the flowers also rapidly lose their volatile aromatic compounds once the flowers have blossomed. It is crucial that these flowers be harvested early in the morning; before the buds have had time to fully open. Even a single hour can result in a dramatic loss of the overall essential oil content of the flower’s petals.

When producing essential oils, distilling the largest yield of oil is not the only consideration. It is equally important that the oil have an optimal chemical profile so it will efficiently exhibit its unique properties. This chemical profile is widely impacted by the season and time of day as plants undergo processes of blossoming, ripening, and maturation. An example of this is juniper, an essential oil derived from the leaves, wood, and berries of the Juniperus phoenicea tree. Overall, this essential oil is composed of a majority of monoterpene and sesquiterpene hydrocarbons. Additionally, the oil contains varying amounts of oxygenated constituents throughout the year. The properties of the oil are highly dependent on the overall profile of the essential oil as well as the ratio of one type of constituent to another. Juniper essential oil has a higher percentage of alpha-pinene in the summer and autumn months (May to November). Interestingly, the oil distilled during this time was also found to have the most powerful antioxidant properties. Collecting essential oils during the timeframe when the oil has an optimal chemical profile is a vital part of ensuring desired properties of the essential oil.

Understanding how botanical physiology is affected by the seasons and time of day allows farmers and harvesters to find a balance between total yield and desired benefits—ultimately resulting in the production of consistent, high quality essential oil products!