Suitability of diverse sub-optimal levels of dissolved oxygen for the cultivation of Pelargonium tomentosum Jacq. in deep water culture hydroponics

Pelargonium tomentosum Jacq. (Geraniaceae) is a herbaceous peppermint-scented groundcover native to the Western Cape of South Africa. This study measured the adaptability and vegetative growth of P. tomentosum to various sub-optimal levels of dissolved oxygen (DO) in deep water culture hydroponics over 74 days. Four different methods of oxygenation namely, passive aeration (control), vortex oxygenation (V), air-pump injection (AP), and a combination of vortex oxygenation and air-pump injection (APV) were applied to 9 replicates. Plant height, shoot weight and leaf number were significantly higher (P≤0.05) in air-pump injected treatment as compared to the vortex and its combination with air-pump injection. While passive aeration (control) had the least healthy roots when compared to other treatments, it had plant height, shoot weight and leaf number that were slightly lower than, and statistically similar to the air-pump treatment. These findings revealed that air pump injection is a suitable oxygenation method in the cultivation of P. tomentosum in a deep water culture system.