rob,
just throwing out some ideas for you. we have 80 acres in a river valley, farm land, corn and soybeans. in the past 5 or 6 yrs, because of droughts and floods, our wildflowers, native plants and non native plants have been wiped out or are not the typical expected blooms.
we asked one of our lease farmers to plant soybeans only. we took back one half acre field from a lease farmer and planted native pollinator species, ie, something blooming all season long. did the same with the other lease farmer, but a buffer of a about a half acre of what he now plants (soybeans). we cleared out the overgrown tree line on that section. in the tree line were/are berry bearing bushes that have come back. we also plant a small amount of buckwheat, and a small amount of clover in different areas.
i guess what i am saying is, if you can, try to plant, if you can, something the bees can benefit from all season long or a variety of, not a one time shot..... not just clover, not just buckwheat, not just dandelions. plant a variety if you can of plants that bloom season long.
we also applied for and received a grant from the usda to restore parts of our land or plant for pollinators. these plants bloom all season long, long road ahead of us on this, it is still in the works.