1. Nectar and pollen are floral resources that provide food for insect pollinators, so quantifying their supplies can help us to understand and mitigate pollinator declines. However, most existing datasets of floral resource measurements focus on native plants found in rural landscapes, so cannot be used effectively for estimating supplies in urban green spaces, where non-native ornamental plants often predominate.
2. We sampled floral nectar sugar in 225 plant taxa found in UK residential gardens and other urban green spaces, focussing on the most common species. The vast majority (94%) of our sampled taxa are non-native, filling an important research gap and ensuring these data are also relevant outside of the UK.
3. Our dataset includes values of daily nectar sugar production for all 225 taxa and nectar sugar concentration for around half (102) of those sampled. Nectar extraction was conducted according to published methods, ensuring our values can be combined with other datasets.
4. We anticipate that the two main uses of these data are (1) to estimate the nectar production of habitats and landscapes, and (2) to identify high-nectar plants of conservation importance. To increase the utility of our data we provide guidance for scaling nectar values up from single flowers to floral units, as is commonly done in field studies.

Nectar measurements of the 225 flowering plant taxa took place in March-October 2018 (220 taxa) or February-April 2019 (five taxa) at field sites in southern England, which included public and private gardens, allotments, garden centres and road verges. Nectar accumulated over a 24-hour period (during which flowers were bagged) was extracted using glass microcapillaries, with sugar concentration measured using a handheld refractometer. See 'Materials and Methods' within the associated paper for a full description of the methods.

See the Metadata tab in the Excel file. This explains what each column represents. See also the 'Usage Notes' section within the associated paper. We anticipate that the two main uses of these data are (1) to estimate the nectar production of habitats and landscapes, and (2) to identify high-nectar plants of conservation importance. To increase the utility of our data we provide guidance for scaling nectar values up from single flowers to floral units, as is commonly done in field studies. In addition, researchers could investigate how phylogeny and floral traits predict nectar production or nectar sugar concentration using statistical models.