Verge gardening is a citizen-led form of public urban greening where residents plant and maintain understorey and trees in the road easement, and it has the potential to significantly increase the diversity and complexity of street greenery which is, most commonly, mown grass and monocultures of street trees. In Melbourne, Australia, two forms of verge gardening – understorey planted by residents and street trees planted by residents– were investigated. The distribution of verge gardens was tested for correlation with a range of urban form and social factors that included the proportion of garden in residential parcels, the proportion of the street set aside as road verge, age of street development, the presence of footpaths, tree cut-outs (tree pits) and social disadvantage. By better understanding the factors associated with verge gardening, we hope planners, urban designers and land managers will be able to better incorporate verge gardening into urban greening strategies and so maximise the biodiversity, ecosystem function and human amenity benefits associated with this significant public activity. We found that verge gardening was common, occurring in almost a quarter (22.1%) of verges and was strongly associated with verges without footpaths, tree cut-outs rather than continuous verges, and verges on local roads rather than collector roads. Neighbourhoods with proportionally more garden had more verge gardening. With the exception of the oldest streets in our study, streets that were newer had more verge gardening than those that were older. The presence of street trees planted by local government was associated with less verge gardening. Verge gardening was less common in neighbourhoods with greater social disadvantage, and spatial contagion increased the likelihood of neighbours having verge gardens. Local government can facilitate verge gardening through engagement, education, adopting alternative street types, using tree cut-outs to better strategic advantage, and targeting areas of social disadvantage.