In the hyper-arid Peruvian-Chilean Desert, fog oasis ecosystems are formed in the hillslopes of the Andean foothills. Urban expansion and climate change are jeopardizing the conservation of these ecosystems with a high degree of endemic species. In the city of Lima, a fog oasis formation, Lomas de Quebrada Verde, has been under local conservation during 20 years; however, conservation has been empirical and without scientific support. The objectives of the present study were to: (i) describe a year-round spatio-temporal pattern of the plant diversity along the study area, and (ii) relate plant diversity and composition with environmental variables [altitude, slope, soil gravimetric moisture (θg) and soil organic matter (SOM)]. A marked seasonality was found in plant diversity, having two pronounced seasons, a dry of low diversity during March and May 2013 and January 2014, and a wet season of greater diversity that occurred between the July and November 2013 evaluations. Altitude, θg and SOM were positively correlated with canopy cover, but not with plant diversity indexes (Shannon-Weaver and species richness). Altitude, θg and SOM were found to have an effect on shaping the plant community composition. Herbaceous species were dominant in the low altitude and low SOM belt. Whereas woody species such as Croton alnifolius and Heliotropium arborescens were more abundant in the higher altitude belt, where SOM was greater and humidity was more persistent along the year.