Planting date impact on flowering, pollinator visitation and yield of mass flowering oilseed crops in the Northern Corn Belt

Declining natural pollinator populations are a potential threat to global food supplies. Mass flowering summer annual oilseeds can provide much needed crop diversity and floral resources to support pollinator communities. We evaluated how managing planting date affects floral phenology, floral accumulation (flower coverage time x flower area), pollinator visitation, pollinator diversity and yield of nine oilseed crops. Borage (Borago officinalis L.), calendula (Calendula officinalis L.), crambe (Crambe abyssinica Hochst), cuphea (Cuphea viscosissima Jacq. x Cuphea lanceolata W. T. Aiton), echium (Echium plantagineum L.), flax (Linum usitatissimum L.), spring camelina (Camelina sativa (L.) Crantz), spring canola (Brassica napus L.) and sunflower [Helianthus annuus L.] were grown in Morris, Minnesota during the summers of 2013 and 2014. Each crop was planted on a "standard" planting date of mid-May and additional planting dates of early May, early June and early July. Shifting planting dates affected flowering phenology, floral accumulation, pollinator visitation and crop yield. Later planting dates led to later onset of flowering for all crops and affected total floral accumulation for crambe, cuphea and echium. Pollinator visitations changed with planting date and were generally greater with the later planting dates. At least two of the four planting dates supported high yield for each crop. The ability to maintain high crop yield across a window of planting dates affords growers management options for their fields and can be used to design complementary resource pairing and improve pollinator health through crop diversification and management.