Variation in pollinator visitation among garden cultivars of marigold, portulaca, and bidens

Due to declines in pollinator populations, many people are now interested in learning about which annual flowers they can plant in their garden to better support pollinators. However, reports of experimental evaluation of cultivars of annual flowers for attraction to pollinators are scarce. We sampled pollinators visiting six cultivars of marigold (Tagetes erecta and T. patula), ten cultivars of bidens (Bidens ferulifolia and B. aurea), and eight cultivars of portulaca (Portulaca oleracea and P. grandiflora) for two years to compare pollinator visitation rates among cultivars within each flower type. Pollinators collected on flowers in research plots were categorized into four groups, honey bees (Apis mellifera), common eastern bumble bees (Bombus impatiens), wild bees, and syrphids, to show the proportion of different pollinator visitors to each cultivar. Pollinator visitation rates varied significantly among cultivars of marigold, bidens, and portulaca, with some cultivars having as much as 10-fold the visitation rate of other cultivars of the same flower type. In the second year we also evaluated nectar production and nectar quality of the most and least visited cultivars of portulaca and bidens. Our results show that pollinators have a strong preference for cultivars that produce the most nectar or nectar with the highest sugar content. This research will better inform entomologists, growers, educators, and plant breeders, about which cultivars of marigold, portulaca, and bidens are visited the most by pollinators, and how to accurately determine this at the cultivar level.