# How Biological and Environmental Factors Affect the Quality of Lavender Essential Oils
## 3 Biological and Environmental Factors Affecting EO Production
### Developmental Factors and Plant Age  
EO quality is variable based on the plant organs used for extraction [14] and depends on plant developmental stages. Remarkably, the amount and constituents of essential oil also vary during inflorescence and floral development [46]. Usually, higher amounts of EO are observed in younger plants, while richer compositions are found in 8-year-old plants [47]. Almost 25% of lavender cultivars grown in Hungary display remarkable differences in their essential oil compounds with plant age [37]. From one year to another, there are variations in the same genotype of lavender. The highest-quality EO composition is obtained from flowers, as shown by [48]; therefore, stems and leaves should be avoided during harvesting. Lavender flowers are 4-5 times richer than leaves in _L. angustifolia_, _L. latifolia_ and _L. x intermedia_; as a result, essential oil from lavender flowers has the finest fragrance [14; 49]. Furthermore, the inflorescence stem accumulates less essential oil than the leaves [50]. The composition of EO is also variable within floral organs; for instance, sepals and gynoecium have 50 times higher EO than petals and stamens [50]. Therefore, the flower developmental stage and ontogeny are fundamental for optimal harvest time [33; 50]. EO accumulation in flowers of Grosso lavandin increases and reaches a maximum at 30% of anthesis, followed by a gradual drop towards senescence [51]. The harvest time considerably affects lavender's production and EO composition parameters [13; 35; 41]. The optimum harvesting stage to achieve the maximum lavender EO content is at 60% blooming [41; 52; 53]. However, in _L. x intermedia_ plants, the ideal harvesting period is at the early stage of flowering [54]. lavender anthesis period, linalool content increases slightly towards the end of flowering, reaching 43.5%. In contrast, linalyl acetate content displays a reverse trend, reaching 18.7% at the end of flowering [26; 31; 37; 55]. Linalyl acetate and several sesquiterpenes attract pollinators during the flowering period [56]. The highest amounts of the major EO components, such as linalool, 1,8-cineole, terpinene-4-ol, limonene and cocime, accumulate in the flower buds and at the end of the flowering period [26; 55; 57]. In contrast, in _L x intermedia_ plants, the linalool content is at a maximum of 50% during the blooming period. On the other hand, the linalyl acetate content is at its optimum at the end of flowering [58]. When the first lavender flowers open, the lavandulyl acetate content is at its maximum [26]. Borneol and bornyl acetate accumulate in immature flowers and leaves [41]. The terpinene-4-ol amount starts to accumulate in the first lavender flowers, reaching the maximum level at the end of the flowering period when the first seeds are mature. Additionally, the amounts of terpinene-4-ol accumulate in mature inflorescences of _L. tatifolia_[59]. Interestingly, lavender EO production is regulated diurnally [13], suggesting that the circadian rhythms affect the biosynthesis of monoterepenes. Table 2 summarises the significant factors affecting the specific compounds of the EO produced by lavender flowers.