The endangered Mexican cycad Dioon merolae has been a nice surprise in our winter hardiness trials, surviving 7 degrees F so far. This was quite a surprise since it hails from the more southern provinces of Chiapas and Oaxaca where it can be found on steep sandstone cliffs near waterways in pine-oak forests. Dioon merolae, named in 1981 after Italian botanist Aldo Merole, forms a slow-growing solitary specimen with 3′ long, stiff, upright, green leaves whose new flush is covered with silvery-grey hairs. We’ll probably never see a trunk in our Zone 7b garden but in warmer zones the trunks can reach 3′ or more. We recommend a dry, sheltered site in climates north of Zone 8b, where it becomes deciduous when temperatures drop below 20 degrees F.
