- June 18, 2018
For millions of years, flowering plants have engaged in an intricate ecological dance, evolving to protect themselves from predators and pathogens while, at the same time, developing ways to attract potential pollinators–both important parts of the plant’s life cycle. Pollinators, too, have been tied up in this tango, a back and forth of creating and overcoming attraction and resistance, access and exclusion, which, over time, has pushed each other to be perfect partners in their biological ballet. Here, we explore the intimate connections plants and pollinators depend on for survival and how this understanding can enhance our own efforts when gardening for wildlife.
A pollinator garden can be more than a name designating a patch of flowers. It’s value can be maximized with attention to colors and patterns and specific shapes and sizes, all orchestrated to play host to a bouquet of chemical cues, impeccably timed to provide the nectar, shelter, and other resources pollinators need as they grow, pupate, and nest throughout the season. By making your pollinator patch a safe and predictable place, pollinators can expect to complete their own life cycles and continue their evolutionary dance with angiosperms.
The plants and practices we choose to use in pollinator gardens can help to diversify the pollinators visiting our gardensopen_in_new. If we want to plant flowers to attract birds and butterflies, we also have to provide for bees and caterpillars, both different, but intimately related parts of the food webs and life cycles that influence the birds and butterflies we see. Managing for the entirety of the life cycle of a diversity of organisms often requires attending to sometimes unfamiliar plant characteristics, like flower color, morphology, and leaf texture, as well as recognizing the impacts of our management practices. For instance, how susceptible are different organisms, say caterpillars, or ground-nesting bees, to any treatments that may be used on the flowers or plant materials.
There are hundreds of thousands of plants in nature, many of which depend on animal pollination and act as important resources for pollinating wildlifeopen_in_new. A small but wonderful selection of those, fortunately, are suitable, even desirable, for home gardens and landscaping. The qualities that attract pollinators to plants are similar to those we appreciate in our own botanicals. Vibrant colors, unique shapes, and pleasant odors make blooming gardens standout against the background of greens and browns, in nature and in our neighborhoods. These features are even more important to the pollinators who are looking for food and to the plants attempting to attract them for pollination services.
- In the Great Plains, leaf cutter bees like lavender and legumes, while sweat bees seek out sunflowers, violets, and saxifrages. Curious about the plant-pollinator relationships in your area? Start with your local eco-region Pollinator Guide.
- Plan on planting for pollinators in full sun, or as much sun as possible. Bees and butterflies require the heat on sunny days to get their wings up to speed and nectar producing flowers are more productive in the sun.
- In typically shady areas, like forested regions, there are going to be native options available for shade gardens–something showy from the surrounding landscape- that will attract hummingbirds and bumble bees, both busy workers in much cooler and darker conditions.
- Select the plants that you love too. It is your garden, create something both you and pollinators will enjoy all year.
The colors we see in our gardens may be attractive but they are not necessarily the same colors pollinators perceive. Many bees, butterflies, and other nectivorous insects have eyes sensitive to ultraviolet light and many of the flowers they pollinate reflect and absorb ultraviolet light in patterns on the petals, called nectar guides, that we cannot see. Visible color is initially used as a long distance attractant for pollinators but ultraviolet patterns on the petalsopen_in_new and flower centers act as bullseyes, or targetsopen_in_new, leading hungry bees and butterflies to the copious nectar.
Colors acting as attractants can also be associated with attracting different types of pollinators. Hummingbirds are generally drawn to reds and oranges while bees and flies are attracted more to blues and yellows. Moths are nocturnal nectivors and white or pale flowers in the dark are more likely to be seen and visited. Butterflies prefer purples and oranges but will nectar on pastel petals like pinks and periwinkle. A diversity of colors and color patterns is important to attract a diversity of pollinators.
- Choose a selection of colors to display across the garden and throughout the season that attracts the types of pollinators you want to see more of. Our simple downloadable, printable, planting palette can help get you started.
- Select straight species, those unmodified from the original native variety, whenever possible. Nativars are cultivars created from native plants with a variety of unique colors or patterns but may not be as attractive to pollinators as they are to the plant breedersopen_in_new.
- Stage your plantings according to height with taller plants in the back or middle and shorter plants at the edges to improve color visibility from multiple and further distances.
Flower sizes, petal shapes, and even the position or angle the flowers are presented can select for, or limit, access to the stamen and nectaries by certain pollinators. Composite flowers, like black-eyed Susan and sunflower, have a flat, disk-shaped flower which acts as a convenient landing pad and offers hundreds of tiny, shallow florets which are easily accessed by most bees, flies, and butterflies. Umbelliferous flowers, like milkweeds and Joe-pye, shown above with a Tiger Swallowtail, offer similar landing platforms and easy access to long and short-tongued pollinators.
More complex flower shapes limit some pollinators’ abilities to gain access to pollen or nectar–this reduces competition for the resource and offers greater reward for the few specialists that can put in the effort. Tubular flowers, like lobelia and beardtongue, are inaccessible to short-tongued bees and most flies unless they have a large flat bottom petal to act as a small landing pad for pollinators who then crawl inside to find their sweet treat. Large carpenter bees have powerful mouthparts and will often just poke or chew a hole through the tubular flower from the outside to reach the nectaries. Hummingbirds and clearwing moths (shown above), are excellent at accessing the tubular flowers of monarda with their very long proboscis.
Nodding flowers, like harebell and the columbine shown above, hang down and are even more difficult to access. Bumble bees, however, can easily reach these deep nectaries with their long tongue and small bees will often crawl up inside, clinging to the floral structures, and perform buzz pollination to collect the protein-rich pollen.
- Increase the variety of flower shapes and sizes available to pollinators when adding flowers to your gardens (look for composite, tubular, nodding, and umbelliferous flower shapes). This can improve the diversity of specialists and may reduce competition for daily pollen and nectar resources among visiting pollinatorsopen_in_new.
- In dense clusters, position the flat, composite, and umbelliferous flowers in the center, with tubular and nodding flowers towards the outsides and edges. This allows for improved access to flowers that are approached from the side or from underneath.
- Again, when acquiring native plants, choose straight species–those unmodified from the original native variety–whenever possible. Cultivar varieties of native plants may have unique sizes and shapes, like double petals, but may not be familiar or even accessible to native pollinatorsopen_in_new.
Plants, especially their flowers, produce varying cocktails of volatile organic compounds giving them specific odors or fragrance, that are picked up by sensilla, small hairs located on many insect’s antennae and mouthparts. These olfactory cues guide pollinators to their source and produce the pleasant aroma gardeners and passers by may stop to enjoy. Butterflies are generally drawn to sweet and spicy scents, while bees are more often found chasing a fruity or flowery fragrance. Flies, on the other hand, are often attracted to flowers smelling of dung, or rotting carrion, but can be found pursuing a host of other odoriferous emanations.
Plants also emit chemical signatures which can be picked up by the sensitive sensilla on pollinators searching for, or avoiding, specific plant qualities. Secondary metabolic compounds produced within plants, such as the pictured pink turtlehead (Chelone lyonii), can act as either toxins or medicines depending on the pollinator and the plant. Pollinators suffering from parasites or pathogens seek out certain, often native, plants with higher concentrations of important metabolites in hopes of medicating themselves against afflictions.
The secondary compounds in plants are especially important to reproducing moths and butterflies which can be very selective about the species of host plants they lay their eggs on. Plants produce these compounds to protect themselves from being eaten. Some of the secondary metabolites produced by plants taste bad to common herbivores, while others are outright toxic. In order to eat enough to survive, insects have had to overcome some of these defenses. As there are thousands of plant defenses out there, insects specialize in getting around at least a few of these obstacles, so they can safely eat a few kinds of plants. Moths and butterflies who detect a certain secondary compound, like this Painted lady on her common sneezeweed (Helenium autumnale) host plant, can lay eggs knowing their offspring will be able to eat when they hatch. Plants that are not native to the same range of the insect do not emit the same familiar signatures and will not attract the insects looking for them.
While some arthropods are generalists who can access, consume, and nest in a large variety of suitable habitat conditions, most–around 90%–are specialistsopen_in_new and require specific plants to complete their life cycle. Specializations can be morphological, like shapes and lengths of mouthparts or body sizes. They can be physiological, like resistance to toxins, or they can be behavioral, as in the habits, timing, and preferences that are synchronous with the habits and timing of flowering plants. This monarch caterpillar eating very toxic and sticky milkweed (pictured), can do so because it has a digestive system that allows it to–a physiological trait–and because it first chews a hole in the midvein of the leaf–a behavioral adaptation–to stop the milky sap from flowing to the ends where it eats, preventing damage to its mouthparts.
- Include plants of different species as well as those from different genera and families. A garden with a couple of kinds of milkweed will be greatly enhanced by the addition of a few aster species. Include shrubs and grasses to provide host plants for hundreds of moth species, as well.
- Skip the chemicals. Holes in leaves are usually a sign of success as hungry growing caterpillars are consuming their host plant. Pest species may be less likely to take over in diverse native gardens because they are controlled by predators like birds and other insects.
- Consider letting a few “weeds” grow in. These may be native varieties of local wildflowers and can attract beneficial insects that may prey on any pest species, keeping them under control. You can remove seed heads as they form to keep from spreading.
Pollinators rely on plants for a myriad of materials as they progress through their lifecycleopen_in_new. Beyond pollen and nectar, some bees collect oils and resins from flowers to line their nests with, which offers waterproofing and antimicrobial benefits to developing larvae. Wool carder bees, shown above, collect pubescence, or plant fuzz, from the leaves and stems of plants like mullein and lambs ear. They too use this to line their nests, which they make in the hollow stems of previous year’s flowers.
Many native bees and other important insects nest in hollow stems and branches; leafcutter bees use little bits of plant leaves to line them and make cocoons, while mason bees use mud to create partitions in the stems and seal up the ends. Numerous moths and butterflies will also depend on the plant leaves and stems to lay eggs, make cocoons, or cozy up for the winter. This, in turn, provides excellent and abundant food sources for nesting birds in the spring and other ravenous wildlife emerginging from their winter slumber.
Since plants provide the necessary materials for foraging, nesting, and overwintering we must take a serious look at the practices we employ when managing that plant material in our yards and gardens. Weeds invade in the spring and herbivores snack all summer. Perennial and annual wildflowers leave behind stems and dried seed heads and shrubs and trees leave leaves in the fall. Winter brings few challenges for gardening but offers opportunities for planning and improving connections.
- Include a variety of textures and leaf types in your native plant selections to appeal to a variety of pollinators looking for nesting materials.
- Avoid nativars (native cultivars) with altered leaf color, like bronzed or variegated patterns. This is shown to be the plant breeding quality with the biggest effect on native pollinators’ useopen_in_new.
- Avoid “cleaning-up” pollinator gardens in the fall and allow the leaf litter and dried stems to persist until late in the spring.
- When spring cleaning before temperatures are consistently above 50˚F, place garden debris–the dried leaves and hollow stems, etc–in a sunny place for a couple more weeks to allow pupating bees and other insects time to finish their development and emerge–just in case.
- To help annual plants, like black-eyed Susans (Rudbeckia hirta), to reseed, allow a thin layer of broken down leaf litter to collect around the base of plants, instead of thick bark mulch. This will help prevent a few weeds and retain moisture like mulch but will also allow newly germinated plants to make it through.
- Leave some bare ground for bumble bees, collettes, and others ground nesting bees to dig in for their nests.
Mutualism between plants and insects is regional. Below are some suggestions for pollinator gardens that will work for almost any location. They are a diverse selection of sun-loving native plants pollinators are known to prefer. Together these picks offer host plants to locally important butterflies or moths, they provide a sequential array of blooms, colors, shapes, and structures both gardeners and pollinators will appreciate, and they supply some of the required resources for nesting bees and overwintering wildlife.
Click on a region button below to download your local garden card and plant list.Northeast Southeast Mountain Southwest
It may seem like complicated lists of dos and don’ts but maintaining a pollinator garden simply comes down to one question; in short, what does nature do? From there you can decide how much planning and organizing to do, how much you want to let go and enjoy, and how much should be taken care of to suit your own preferences. Many people find the challenge of assembling a diversity of plants tailored for their region and regional pollinators a delightful and satisfying hobby.