Optimization of harvest regime and post-harvest handling in geranium production to maximize essential oil yield in Rwanda

In Rwanda, the production of geranium (Pelargonium sp.) essential oil is becoming an important commercial crop for income generation. The understanding of postharvest handling of the crop prior to distillation is a key strategy to maximize oil yields. Two experiments were conducted in commercial fields of rose geranium, Pelargonium graveolens, in Kiyombe (Rwanda) to investigate the effects of (i) the length of dry-down or partial wilt and (ii) the time of day on the quantity and quality of essential oil yield and composition. In the first study, the plant material was harvested at 12:00 noon, and while drying also under the same shade conditions the material was sub-sampled immediately and again at 3 h intervals up through 46-h after harvesting. In the second study, the geranium plants were manually harvested at 10:00 AM, 12:00 noon, 2:00 PM, and 4:00 PM and dried under shade for 17 h prior to steam distillation. The geranium plants harvested in the early afternoon (2:00 PM) had the highest essential oil concentration (0.22%). The chemical profile of the essential oil showed that Kiyombe geranium oil exhibited a suitable chemical composition (citronellol 26.4%, linalool 2.3% and geraniol 13.9%), acceptable for international markets.