This datafile consists of a subset of plant phenology observations drawn from the USA National Phenology Networks National Phenology Database (www.usanpn.org). The data were collected by citizen and professional observers and archived and distributed by the USA National Phenology Network. Protocols are available in Denny et al. (2014). This datafile consists of plant phenology observations that were used in an effort to construct predictive models of phenophase transitions using accumulated growing degree days based on PRISM daily minimum and maximum temperature data. The phenology data were queried from the USA National Phenology Network on 9-25-16.