I have ticseed flowers, Mexican heather, and zinnias; but no bees or butterflies. At the nursery, the bees were loaded on the Mexican heather, so I bought one plant and none are coming to my garden. I admit I'm only growing one of each plant (except zinnias) but pollinators aren't coming. I have 7 milkweed plants, and butterflies are laying their eggs on it. Why don't they stay for nectar?