Bud Burst Mobile is a smart phone application for an environmental Participatory Sensing project that focuses on observing plants and collecting plant life stage data. The app was initially designed for record-keeping and motivation to participate in this project has been based on improving scientific knowledge. To test other methods for motivating data collection and increasing user retention, we added an outdoor game activity, similar to geocaching, called flora caching. Players gain points and levels within the game by finding and making qualitative observations on plants. Location-based information is included in the game with the display of local lists of plant species occurring in a user's area derived from governmental data sources. Additionally, user-collected data and the occurrence of species on the local lists obtained from the photo-sharing website Flickr are displayed on an interactive map. Administrator targeting of individual plants facilitates expert control over crowd-sourced data collection for species of interest. We evaluated these additional features with the help of 50 volunteers playing on the UCLA campus as a case study. Results indicated that participants were highly motivated by the flora caching game, and next-most by the knowledge that environmental scientists will use the data collected for studying the effects of global climate change. Other motivating features included sharing plant observations with other users and the information contained in the local lists of plants.