Blades, Lyn, Geoffrey Harper, Stephan Helfer, Maria Luisa Lee, Liz Rogers, and Sandra Stewart. “Rapid-Survey Methods for Flowering Phenology”. Sibbaldia: the International Journal of Botanic Garden Horticulture, no. 6 (October 31, 2008): 163–179. Accessed May 5, 2024. https://journals.rbge.org.uk/rbgesib/article/view/41.