How Environmental Factors Affect Oil Quality
The production of essential oils in plants is a reaction and adaptation to environmental circumstances. Because of this, environmental factors such as elevation, climate, soil health, water abundance and temperature can impact the health, vitality and essential oil production by medicinal plants. These variables, among others like harvest time and processing conditions, influence the quality and quantity of essential oils the plants produce. To gain a better understanding of the effect each of these factors has on oil quality, we’ll talk about each individually.
Native Climate and Country of Origin
The native or indigenous region where a plant originates, naturally has the ideal climate and best growing conditions. These conditions encourage plants to produce aromatic compounds in the most idyllic proportions. Selecting sources already within the plant’s native region eliminates the need to attempt to recreate unique combinations of soil texture and chemistry, humidity, elevation, wind conditions and annual precipitation levels among other variables. Using plants grown in their native climate or country/region of origin (whenever possible) ensures the optimal conditions for producing the highest quality oil.
Research shows that elevation has an impact on the presence and potency of essential oil chemical constituents. One example, is Stachys lavandulifolia (Betony), at 1600m above sea level, measured 47 constituents, whereas at 3200m, it produced 64 (7). There are many important environmental aspects of an ecosystem that change with elevation. The height above sea level can affect temperature, relative humidity, wind speed, water, and sunlight rates among other factors. Because of this, as altitude changes, the plant’s chemical make-up will also change to reflect its growing conditions.
A major aspect affecting the quality of essential oils, is accurately timing the harvesting of the crops. Because plant’s chemical content changes throughout its life, harvesting at the proper time is vital for proper essential oil chemical composition. There are unusual instances when there only days of optimal harvest. Knowledgeable growers understand the proper flowering time of the plants they grow, and the influence this has on essential oil composition.
Chemical changes that take place before, during and after flowering can produce extreme variations in oil composition. Artemisia annua L., when harvested before, during and after flowering, was found to have the highest free radical scavenging activity of the essential oils during full flowering stage(5). “The chemical changes occurring during the entire life cycle of the Vietnamese Artemisia vulgaris have shown that 1,8-cineole and b-pinene contents before flowering were below 10% and 1.2%, respectively, whereas at the end of flowering, they reached values above 24% and 10.4% (Nguyen et al., 2004)”(2). Although growers have understood the importance of timing and have developed precise timing, thanks to technology such as macro-distillation and gas chromatography (GC) techniques, timing has become increasingly exact.
There are rare instances where even the time of day can influence yield. The oil yield of rose will decrease as the daily temperature increases. To ensure the highest content, rose petals must be harvested between 6 to 9 a.m. “In the case of oil glands imbedded within leaf structures, such as in the case of eucalyptus and pines, oil yield and oil quality are largely unaffected by time of harvesting”(2).
Although the need for exactness in timing may vary from time of season, to before, during, or after flowering, or even to time of day (depending on the plant), harvest timing remains extremely important and growers are constantly improving.
Soil & Water
Soil and water are not subjects often discussed when it comes to their impact on essential oil quality and yield. One reason for this, may be that when it comes to soil nutrients, watering schedules or water stress (drought), the impact these have on essential oil producing plants can vary widely. For example, research suggests that Thymus vulgaris L. oil outputs are increased by maintaining optimal availability of water, whereas “…moderate water stress imposed on sweet basil resulted in higher oil content and greater total oil yield”(4). Soil studies are similar in that they are generally aimed at discovering how specific plant types deal with differing conditions to find the optimum environment for each specific plant type. Reputable growers keep up to date on the latest research as their findings can have a direct impact on important aspects of plant health.
In the end, it’s all about finding sources that understand the correct processes to produce the highest quality oil. The best sources are growers who use the latest technology and techniques to increase the health of their crops to produce the best oils. Growers who farm using the best methods, in the plant’s native location, using sustainable techniques, whose oil consistently tests completely pure and with the highest potency, are those who become the best sources.
- Mahdavi, et al (2013) Investigating the altitude effect on the quantity and quality of the essential oil in Tanacetum polycephalum Sch.-Bip. polycephalum in the Baladeh region of Nour, Iran. China Journal of Natural Medicine. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/24359783
- Baser, K. H. C., & Buchbauer, G. (2016) Handbook of Essential oils, science, technology, and applications. (2nd Ed) Taylor and Francis Group; Boca Raton, USA. Retrieved from https://books.google.com/books?id=JXe9CgAAQBAJ&pg=PA136&lpg=PA136&dq=how+do+harvesting+techniques+affect+the+quality+essential+oils&source=bl&ots=ktUec6-nAp&sig=xq7ng-6KP3aucaYawEE2KnPUPZQ&hl=en&sa=X&ved=0ahUKEwj2o4aQhs7NAhUhzIMKHSzsBOsQ6AEISjAG#v=onepage&q=how%20do%20harvesting%20techniques%20affect%20the%20quality%20essential%20oils&f=false
- Saharkhiz, M. J., Kamyab, A. A., Kazerani, N. K., Zomorodian, K., Pakshir, K., & Rahimi, M. J. (2015). Chemical Compositions and Antimicrobial Activities ofOcimum sanctum L. Essential Oils at Different Harvest Stages. Jundishapur Journal of Microbiology, 8(1), e13720. http://doi.org/10.5812/jjm.13720
- Eiasu, B. K., Steyn, J. M., & Soundy, P. (2009). Rose-scented geranium (Pelargonium capitatum× P. radens) growth and essential oil yield response to different soil water depletion regimes. Agricultural Water Management,96(6), 991-1000.
- COŞGE ŞENKAL, B., KIRALAN, M., & YAMAN, C. (2015). The effect of different harvest stages on chemical composition and antioxidant capacity of essential oil from Artemisia annua L. Journal Of Agricultural Sciences, 21(1), 71-77.
- Petropoulas, S.A., Daferera, D., Polissiou, M.G.,, Passam, H.C. (2008) The effect of water deficit stress on the growth, yield and composition of essential oils of parsley. Scientia Horticulturac 115 (2008) 393-397. DOI: 10.1016/j.scienta.2007.10.008 Retrieved from https://www.researchgate.net/publication/248478000_The_effect_of_water_deficit_stress_on_the_growth_yield_and_composition_of_essential_oils_of_parsley_Sci_Hort
- Mahzooni-Kachapi, et al. (2014) The effects of altitude on chemical compositions and function of essential oils in Stachys lavandulifolia Vahl. (Iran). International Journal of Aromatic Plants. ISSN 2249-4340. Vol. 4, No 2, pp. 107-116, June 2014. Retrieved from http://www.openaccessscience.com/pdf-files/vol4_2_jun2014/IJMAP_4_2_5_Stachys_lavandulifolia.pdf