ARS | Publication request: Effect of High Temperature on Extreme Substrate Acidification by Geranium

Submitted to: Southern Nursery Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 7, 2007
Publication Date: August 9, 2007
Citation: Taylor, M., Nelson, P., Frantz, J. 2007. Effect of High Temperature on Extreme Substrate Acidification by Geranium. Southern Nursery Association Proceedings, Atlanta, GA, August 9-11, 2007.

Technical Abstract: The cause of sudden substrate pH decline by geranium is unknown and it may be due to high temperature and/or low P. ‘Designer Dark Red’ Geraniums were grown in two experiments and the first tested the effect of four temperatures (57/50, 64/57, 72/64 and 79/72º F day/night) on substrate acidification. With increasing temperature, substrate pH declined from 6.8 to 4.6 at 63 d. Tissue P was lower in the three highest temperature treatments and it was unclear whether the cause of acidification was due to P deficiency and/or high temperature. The second was a factorial experiment with the three highest temperatures from experiment one by 5 pre-plant P rates [0, 0.56, 1.13, 2.25, 4.50 lb triple superphosphate (TSP) • yd-3 substrate]. At 63 d in the 0.56 and 1.13 TSP treatment, tissue P was not significantly different and pH decreased with increasing temperature from 5.6 to 4.8 and 5.9 to 4.7, respectively. At the 2.25 TSP treatment tissue P was similar at the two higher temperatures and pH decreased as temperature increased. In the highest P treatment all tissue P levels were adequate and pH declined with each increase in temperature. When plants received P, pH fell to below 5.2 by 57 d when temperature was high. These data indicate high temperature-stressed geraniums increase acidification rate independent of tissue P, which offers one explanation for sudden substrate pH decline.