Rhus is a genus of shrubs that produces strong aromatic essential oils. These oils have numerous applications, including treating urinary infections, flavoring food, and alleviating gastrointestinal ailments. We conducted an experiment to track the essential oil yield and composition of two Rhus species, Rhus aromatica Aiton and Rhus trilobata Nutt., over the course of the growing season. The essential oil yield and composition were examined over four weeks from May to June 2023. We found that higher ambient temperature lowered the total yield of essential oils. Yield decreased in both species over the course of the experiment, with a yield of 0.21% in week 1 and 0.07% in week 4. The composition of oils changed as the outside temperature increased. Some of the lighter hydrocarbons, such as limonene, decreased, while other heavier hydrocarbons, including β-caryophyllene and germacrene D, increased as the outside temperature rose. Limonene was also shown to be the main component of R. aromatica essential oil at an average of 86.2% area, with >98% of that being the enantiomer D-limonene. Additionally, the effect of different drying methods on the yield and composition of the essential oils was investigated. The results show that when drying the plant material in the oven, a greater yield of 0.31% is obtained, whereas the shade- and sun-dry methods yield 0.09% and 0.02%, respectively. The main component of R. trilobata was α-pinene compared to the D-limonene in R. aromatica. This study helps to understand more of the correlation between outside temperature and essential yield/composition in the species R. aromatica, particularly during the May–June sampling period. To compare two Rhus species that get commonly grouped together as the same species, SPME Headspace was used to determine that the main component of R. trilobata was α-pinene compared to D-limonene being the main component in R. aromatica.