Among the many joys of herb gardening is the chance to observe the abundance of wildlife that visit—the industrious bee, the fleeting butterfly, hovering hummingbirds and more. Of course there are other, less-welcome visitors—the hungry rabbit or mischievous raccoon—but still, most of us would agree that a garden without wildlife seems static and even sterile.
While seeking food, water, shelter and nesting sites in and around our herb gardens, many of these animals and insects are also engaging in the valuable mechanism of pollination. Plants and their pollinators have co-evolved to acquire physical traits that attract one another in a mutual relationship, making sure pollen is carried from one flower to another. In addition, the flowering cycles of the plants have evolved to be closely aligned with the life cycles and needs of their pollinators. Together these characteristics form what is called a pollination syndrome. Using knowledge of these syndromes, herb gardeners can learn to attract and increase pollinator numbers, making for a healthier and livelier landscape.
The Facts of Life: Fertilizing Flowers
Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma of another flower. When this transfer is successful, fertilization occurs, which leads to seed development and fruit production, thus guaranteeing the plant’s continuing existence.
Eighty percent of all plants rely upon pollination for survival. But more astoundingly, for humans, one out of every three bites of food is made possible by pollination. Without pollination, say goodbye to cabbage and avocados, watermelons and coconut, and more tragically, strawberry shortcake, blueberry cobbler, apple pie, and chocolate anything. Hamburgers also can’t happen without the pollination of alfalfa to feed cattle. As it turns out, pollination hits all of us very close to home.
Pollinators are keystone species, meaning that a large number of other species depends upon them for their existence. Pollinators are also considered an indicator species, with their well-being connected intimately with the bigger picture of overall environmental health. Dramatic declines in pollinator populations are attributed to three main factors: loss and fragmentation of habitat, degradation of remaining habitat, and pesticide poisoning.
There are two types of pollination—biotic and abiotic. Eighty percent of all pollination is biotic, meaning carried out by animals. Abiotic pollination is accomplished by wind or water, the vast majority by wind.
Grasses are an example of plants pollinated by wind; they produce fine grains of pollen in copious quantities to allow for the vagaries of the weather, while at the same time vexing human beings with annoying allergies. Corn and wheat, for instance, are dependent upon the wind for pollination.
All other pollination is performed by a variety of animals ranging from the tiny tachinid fly to the rather large and unlikely lemur. The most common pollinators are birds, bees, butterflies, beetles, bats, ants, moths and flies. It can be said that flowers are the tools plants use to make seeds and thereby fulfill their genetic destiny.
Floral strategies to attract pollinators take many forms, such as visual cues, food, scent, mimicry and entrapment. Visual cues are most evident in flower color and shape, and sometimes, a nectar guide is present. A nectar guide is like an arrow on a road map indicating the location of nectar in the form of veining or pattern on flower petals. Sometimes these guides are only visible in ultraviolet light. Nectar is the obvious reward for many pollinators in searching out plants; it is a rich cocktail of sugar water, amino acids, minerals and vitamins. Some insects will also eat some of the pollen that they are intended to carry. The scents that attract various pollinators range from highly fragrant to putrid. Some flowers will mimic the very insect they need for pollination by posing as a possible mate. Lastly, some plants will lure pollinators only to trap and then dissolve the unsuspecting victim.
Beyond that, plants have evolved with different flowering times throughout the growing season to decrease competition and provide pollinators with a constant food supply. In turn, these pollinators have adapted with specialized body parts and behaviors to transport the pollen from one plant to another.
Bees: Efficient Pollinators
Herb gardeners are well aware that bees love herbs; blooming herbs almost vibrate with their activity as summer arrives. Bees especially love lavender, thyme, mint, marjoram, oregano, borage and bee balm, among others. But what is it that actually attracts them?
The pollination syndrome of bees tells us that they select brightly colored day-blooming flowers, full of nectar, often tubular in shape, with a structure that provides a landing platform. Bees are said to prefer flowers of blue or yellow, although it is not unusual to see them on blossoms of any color. Their favorite flowers also emit a sweet or minty fragrance. Beyond that, it depends upon the length of their tongue whether they visit a plate-like calendula or a cup-like sage.
Since there are about 4,000 different species of bees, plants appeal to them through plenty of variations. Bees are grouped by their nest-building behavior and by whether they are solitary or social. While the commercial honeybee may live in the iconic white box hive, just over two-thirds of bees are ground-nesters. They lay their eggs or tend their larvae in burrows where they provision individual cells for their young. The rest are wood-nesting, constructing homes in mostly abandoned beetle larva tunnels or dry cavities of dead trees, and sometimes man-made structures like hollow walls and barns. Others will parasitize and rob the nests of other bees.
Solitary bees are not loners; they actually live in an aggregation with other solitary bees, but they only tend their own nests. Mason bees, leafcutter bees and carpenter bees are examples of this category. Solitary bees may take up to a year to complete their life cycle, and pupae can lay dormant during cold and drought, waiting until conditions are more favorable.
Social bees (like the honeybee and bumblebee) form colonies where they build nests together and tend young in a more complex hierarchy of queens and workers. Turnover is high, with development taking four to six weeks.
Most solitary bees are polylectic, meaning that they feed and gather pollen from a large number of flowering plants and can adapt to changing availability of food sources. Others confine themselves to a particular plant family and some even are dependent upon a single plant species. These latter types are most at risk from habitat loss.
Social bees are also polylectic. Herb gardeners who observe bees systematically mining a particular group of herbal flowers at a time are seeing a behavior called “flower constancy,” where bees feed from a single species on a particular foraging trip.
Prolific and efficient, bees are the most successful pollinators; they can gather and deliver large amounts of pollen on the stiff hairs of their bodies or carry it in specialized body parts, or pollen baskets. It is alarming that bees are now under threat; entomologists believe that environmental stress, disease and parasites are acting alone and/or in concert to cause a worrying decrease in numbers.
Birds Rely on Sight to Find Nectar
Birds have no sense of smell, so pollinating birds rely instead on their keen vision to search out flowers with deeply hidden nectar. Once they find their food source, hummingbirds and other nectar-eating birds are dusted around their faces with pollen that they then take to the next flower. Some birds accomplish pollination while hunting for insects and spiders concealed within flowers.
Of the 2,000 species of bird pollinators across the globe, hummingbirds are the best-known and most beloved. They need to eat several times their weight in nectar every day to maintain the frenetic pace of their beating heart: more than 1,000 beats per minute! It is pure joy to watch them hover and feed among the flowering herbs in our gardens.
The tiny birds possess an eagle’s eye to spot their favored red, orange and yellow flowers but they are also seen frequently feeding on the blue blooms of herbs like catmint and sage. Their slender pointed bill and long tongue are adapted to probe tubular, funnel-shaped flowers such as lobelia and nasturtium. Beyond the herb garden, hummingbirds are a key species responsible for wildflower pollination.
Butterflies are Determined
Butterflies are less efficient than bees but just as persistent at pollination. Butterflies see the red flowers that bees cannot. They use their long tongue (called a proboscis) to siphon nectar from suitable flowers, while their brushy bodies accumulate pollen grains. Butterflies need a flower structure that supplies a landing platform on which to perch while feeding; bright, day-blooming flowers growing in clusters or umbels meet this description. In the herb garden, butterflies love the blossoms of chives (Allium schoenoprasum), thyme (Thymus spp.), basil (Ocimum spp.), coneflower (Echinacea spp.), pot marigold (Calendula officinalis), yarrow (Achillea spp.), garlic chives (Allium tuberosum) and butterfly weed (Asclepias tuberosa), among others.
Moths Go for Pale, Moon-Lit Flowers
Moths need the same landing platform as butterflies, but since they fly at night their targeted flowers are white or other pale colors better seen in moonlight. Often these flowers only open in late afternoon or evening. Besides their color, evening primrose (Oenothera spp.), yucca (Yucca spp.), mayapple (Podophyllum peltatum), and tobacco (Nicotiana tabacum) smell good to moths.
Beetles Visit Ancient Species
Beetles were one of the first pollinators and therefore visit ancient species like magnolia. They look for white, dull or pale green day-blooming flowers shaped like bowls with the sex organs exposed for effortless access. However, they will also attend small flower clusters with easily available pollen, like goldenrod (Solidago spp.) or butterfly weed (Asclepias spp.). They are attracted to fruity, spicy and sometimes fetid scents. Roses are among the flowers pollinated by beetles. Water lilies use a devious system of entrapment to achieve pollination; luring the beetle to its luminous inflorescence, it drowns the unsuspecting insect in the liquid that covers the female flower part, leaving the pollen to settle to the bottom of the bloom.
Flies are Fascinated with Dull Flowers
This group of pollinators includes gnats and mosquitoes—yes, mosquitoes. It is usually the syrphid, or flower flies and tachinid flies, that do the job of pollination. They are drawn to dull green, white, cream or even dark-reddish brown flowers, some with translucent patches upon the petals, often with unpleasant odors. As annoying as midges are, they make chocolate possible. They are enticed to the small, white downward-facing flowers of the cocoa plant (Theobroma cacao) by the flowers’ mushroom-like smell.
Ants and slugs do their part in pollination by crawling into low-growing, inconspicuous flowers like that of wild ginger (Asarum canadense). Bats pollinate more tropical herbs like mangoes, figs and guavas, as well as the agave from which tequila is made. Larger animals such as honey possums are known to pollinate eucalyptus.
Help Conserve and Support Pollinators
The very act of planting an herb garden is a big first step in helping conserve pollinators. So all herb gardeners have already progressed to the point where they can fine-tune their gardens to increase the number and variety of pollinators that visit.
The fun part of this effort, if it can be even called that, is planting more flowering herbs to serve as foraging habitat. Whether using herbs or not, there are four important characteristics to follow when establishing the habitat.
• It should incorporate a succession of flowers in order to provide blooms throughout the entire growing season.
• It should have several different species in bloom at a time.
• It should combine annuals and perennials.
• It should be free of pesticides.
One example of a pollinator-friendly herb garden might be starting with purple garden chives (Allium schoenoprasum), sweet woodruff (Galium odoratum) and thyme (Thymus spp.) in spring; adding summer-blooming bee balm (Monarda didyma), chamomile (Matricaria chamomilla) and borage (Borago officinalis); ending with late-blooming Joe-pye weed (Eupatorium purpureum), hyssop (Hyssopus officinalis), calamint (Clinopodium spp.) and garlic chives (Allium tuberosum).
There should be a diversity of flower shapes to accommodate the different mouth parts of all of the pollinating insect and birds. Offering a spectrum of colors will attract more pollinators. But, it is best to plant blocks of color, at least four feet in diameter, of each species to help the pollinators locate the food source. This also supports the behavior of flower constancy.
Native plants that have evolved along with the pollinators are the best food sources, allowing pollinators to forage most efficiently. Native mints, clovers and coneflowers are just a few likely candidates, among a very long list of possibilities. Consulting a university extension website to identify plants native to your region would be advisable.
Leaving the garden a little untidy can be a good thing for pollinators. Allowing spent herbs to stand over winter provides nesting and overwintering sites for pollinating insect adults, larvae and eggs. For the same reason, unless it is a danger, leaving a dead tree can be an important component in building habitat. Other common landscape (evergreen hedges, rock walls, stone patios, mulched paths) can shelter pollinators during their life cycle. Water sources can be bird baths and even puddles. Leaving some bare ground gives a home to ground-nesting bees. Butterflies need damp spots to “puddle” or siphon nutrients from the ground.
The Challenges of Pollinator Conservation
As pollinators struggle to survive in a changing world, it seems unlikely that one individual herb gardener can do much for the daunting task. In fact, in The Forgotten Pollinator (Island Press, 1997), Stephen L. Buchmann states fatalistically, “Alone, a small garden for pollinators can’t conserve threatened or endangered pollinators or plants, but it can remind people of the primacy of the precious keystone relationships between them.”
But if we imagine a series of small habitats, a corridor of interconnecting “patches” of pollinator-friendly properties, eventually the fragmentation might lessen. It would also heighten awareness of the problems facing this miracle of nature that is often taken for granted.
A truly successful herb garden is one where pollinators find food, water, shelter and nesting sites. The presence of fluttering birds and buzzing insects only builds upon the joy we find in our gardens, while adding another link in the chain of habitats to help ensure the survival of these invaluable creatures.
Rhonda Fleming Hayes was a university extension master gardener for more than a decade. Now she writes at www.thegardenbuzz.com.
Butterfly Bait: 20 Herbs to Entice Butterflies
Plant these pretty herbs and watch your garden come alive with butterflies. These varieties are of particular interest to butterflies and some moths because they offer a “platform” where the butterflies can alight while they sip their meals.
• Basil (Ocimum spp.)
• Butterfly weed (Asclepias tuberosa)
• Calamint (Clinopodium spp.)
• Caraway (Carum carvi)
• Chicory (Cichorium intybus)
• Chives (Allium schoenoprasum)
• Coneflower (Echinacea spp.)
• Dill (Anethum graveolens)
• Fennel (Foeniculum vulgare)
• Heliotrope (Heliotropium arborescens)
• Hyssop (Hyssopus officinalis)
• Lavender (Lavandula spp.)
• Lemon balm (Melissa officinalis)
• Mint (Mentha spp.)
• Oregano (Origanum vulgare)
• Pot marigold (Calendula officinalis)
• Rose (Rosa spp.)
• Sweet marjoram (Origanum majorana)
• Thyme (Thymus spp.)
• Yarrow (Achillea spp.)
Build a Plant Bridge for Pollinators
When we increase the number of avenues through which pollinators may safely and successfully travel from one plant population to another, we help make genetic diversity among our native plants more secure. With this goal in mind, The Herb Society of America has created its GreenBridges program.
Certified GreenBridges gardens serve as corridors for the movement of birds, bees and butterflies that pollinate native herbs. GreenBridges also serve as networks connecting those with shared interests, providing opportunities for communication, education and research. For more information, contact HSA Headquarters at (440) 256-0514. And if you do create a GreenBridges certified garden, please let us know (firstname.lastname@example.org) and take photos. We’d love to share the information with our readers!