For animal-based pollination to work, the plants must bloom when their pollinators are active, and the pollinators must be adapted to the structure of the flowers. There are pollinators that are most active in spring, and others that develop later in the year. Flowers that rely on pollinator animals are often colorful, large, have a scent that may be pleasing, or offensive, to humans, produce a good amount of nectar and may have special arrangements of pollen that are easily seen by insects. These traits are used to attract pollinators.
Flat, shallow flowers are best for many types of pollinators, especially those with short tongues, to land on and drink from. Native sunflowers (Helianthus spp. and Heliopsis helianthoides), asters (Symphiotrichum spp.) and many other members of the aster family are examples.
Flowers with elongated, tube-shaped blooms and nectar deep inside are visited by long-tongued pollinators. Beardstongue (Penstemon spp.), false dragonhead/obedience plant (Physostegia virginiana) and columbine (Aquilegia canadensis) are among the species with tubular flowers. They may include a landing platform for pollinators on the bottom of the tube. Ruby-throated hummingbirds (Archilochus colubris) prefer red, tube-shaped flowers with no landing platform. Some moths are attracted to white or dull-colored, tubular flowers that are open at night.
Beetles are attracted to bowl-shaped flowers with strong fruit odors.
Other pollinators are generalists and visit all types of blooms.
Some flowers do not need pollinators to fertilize them. There are flowers that self-fertilize. Wind-pollinated flowers are often small, with no petals and dull-colored. Water is used to pollinate other flowers. Some flowers produce little pollen and nectar, often because of selective breeding by horticulturists that has been used to enhance their color, flower size, blooming period, disease resistance or other factors. They may look pretty in your garden, but they do not attract and are not helping native pollinators.
When planning your pollinator garden, try to include a variety of flower shapes as well as colors. Watch the flowers over the growing season to see which ones are visited regularly by pollinators and which ones are ignored. Try changing species the following year, if needed, to include more flowers that are friendly to pollinators.