Narrow-leaved Milkweed (Asclepias fascicularis) is a native, perennial herb distributed along the west coast from Baja California to Washington. It is normally emergent between March and October and experiences die-back in the winter. It is well known for being one of the larval host plants for Monarch butterflies (Danaus plexippus). We explore whether changes in phenology are predicted under future climate models, and speculate on possible impacts to monarch breeding phenology. Specifically, we use the maximum entropy habitat modeling software MaxEnt, climactic data from BioClim's Global Climate Data database and, plant location data from the UC Jepson Consortium of Herbaria, to investigate possible changes in the growing season and growing range of A. fascicularis under future predicted climatic conditions. The results show that, over the next few decades, potentially suitable growing conditions are likely to occur in every month (including months where the plant is currently dormant). This is especially true for the immediate coast, which is the same area where many Monarchs congregate to overwinter. The results suggest a temporal and/or geographic shift in Monarch's breeding habits, with the potential for a naturally occurring year-round breeding population.