Wednesday, June 13, 2018

Pollinators and Flowers in the Wildlife Garden: What Goes With What?

Asters with Sweat Bee
Mary Van Dyke
This year, June 18-24 is National Pollinator Week. Arlington’s Central Library Organic Vegetable Garden and the Wildlife Garden are already buzzing with bees and other insects. This Wednesday’s Library Garden Talk featured Laura Beaty (Virginia Native Plant Society) and Yu-hsin Hsu (volunteer manager of Central Library’s Wildlife Garden) showcasing both the beauty of the flowers, and also the interactions and relationships between pollinators and native flowering plants. Many pollinators have coevolved in symbiotic relationships with a specific plant over millions of years. A pollinator may need that flower’s nectar and pollen to thrive. At the same time a plant may have evolved defense mechanisms against herbivory. How do these complex dynamics play out in the ecological community of a garden? As a gardener, how can I help to grow these mutual connections between flowers and insects?
Arlington Central Library Wildlife Garden in July
Mary Van Dyke
Grow Community in the Garden by planting to:
  • Extend the season of flowers, and 
  • Increase biodiversity in your garden
Grow a range of flowers for beauty in the garden and to provide essential food for pollinators that feed on nectar. Choose a selection of flowers, so that you have different kinds of flowers blooming from early spring to late fall.

Early Spring Flowers For example, in early spring, Golden Ragwort (Packera aurea), Bloodroot (Sanguinaria canadensis), and Moss Phlox (Phlox subulata) flower and have nectar that provides food. Here is a selection of spring flowers for part shade, each flower offers pollinators a nectar reward.
from Covering Ground, Mary Van Dyke, 2018
Mining or Ground Nesting Bees
Some of these flowers might provide nectar for early-emerging Mining Bees or Ground Nesting Bees (often Colletes or Andrena species). The bees then in turn pollinate the flowers as they travel from flower to flower. This spring, did you notice any mound-nests of a Mining Bee colony on a piece of bare earth? Mining Bees are solitary, but live in a colony. Once mated, the female Mining Bee is a single mother. She digs a nest on a slight slope, lays eggs, and feeds her larvae pollen. These bees are not aggressive and seldom, if ever, sting. They may fly around and be a nuisance for a few weeks while males (that can not sting) are engaged in mating displays. These Mining Bees do not harm vegetation. They may be pollinating a specific plant or perhaps pollinating a local fruit orchard. Remember to "let them be" as beneficial insects, even if this bee presence surprised you. The US has over 4,000 kinds of native bees, and many are ground nesting. Virginia has over 200 kinds of native bees in addition to the non-native Honeybee. That’s a lot of different kinds of bees. Some bees are ‘generalists’ and feed off several flower-types, some like the Bumble Bee and the Mining Bees are more specific.

Bumble Bees
This evening in early June, several Bumble Bees are choosing to forage on Penstemon digitalis.
The Bumble Bees have long tongues to reach into the tubular flowers and are guided by the
pink stripes on the petals. Although it is dusk, the bees are still busy foraging. In the photo, a female Bumble Bee worker is visiting a Penstemon flower. The Bumble Bee is lured into the flower by the nectar reward. She has pollen grains sticking to her body, and will visit many flowers and pollinate them as she goes.
Bumble Bee feeding on Penstemon digitalis at dusk
in Arlington Central Library Wildlife Garden
Mary Van Dyke
In the late autumn, the queen Bumble Bee mates. The queen overwinters and lays her fertile eggs in the spring. When she emerges in the spring she is hungry, and needs to eat pollen to get strong. The first emerging worker Bumble Bees are female. They collect nectar and pollen and make a bee bread to feed the other larvae, some of which will be males.

Does it seem like the bees visit some flowers twice?
How often does a flower recharge with nectar?
What are the risks and rewards for the pollinator?
These are topics for more science research: some flowers, such as the Penstemon can resupply nectar every few hours.

Each morning the Bumble Bee decides which flower type to go to, this adaptive behavior is
flower constancy” or "traplining". Bumble Bees are very selective pollinators, in that they effectively pollinate one kind of plant. Honeybees are not so selective. If you follow a Honeybee in the garden you will see it likely visit different kinds of flowers, that may be not so efficient for pollination of one species of plant.

Sweat Bees
In the Library Wildlife garden, I notice Fleabane (Erigeron pulchellus) and Golden Alexanders (Zizia aurea) are nectar sources for smaller Sweat Bees (Augochlora and Agopostemon species).

There maybe three generations of the smaller Sweat Bees in a season. Some of these bees are small, iridescent flashes of green. Sometimes I might mistake them for flies. Sometimes a Sweat Bee lands on my arm to drink sweat. The males never sting, and females very rarely sting, unless in self-defense. So I watch these Sweat Bees quietly feeding and collecting pollen to provide food for their expected larvae. The Fleabane flowers bloom, and if pollinated, will make a seed. Annual plants, such as the Fleabane, tend to make a lot of seeds in order to reproduce and ensure succession.

Sweat Bee on Fleabane
Mary Van Dyke, June 2018

Golden Alexanders, Zizia aurea
Mary Van Dyke

Black Swallowtail Caterpillar on Zizia aurea
Photo source:
Black Swallowtail Butterfly on Dogwood
Mary Van Dyke

Plant Family to Host the Black Swallowtail Caterpillar
The Golden Alexanders, Zizia aurea, is from the Parsley/Carrot Apiaceae plant family and is a host plant for the Black Swallowtail Butterfly caterpillar.
Also you can plant carrots and parsley to support the mother Black Swallowtail butterfly finding a place to lay her eggs, and to host these beautiful caterpillars and the butterfly parents through the summer season.

Basswood, Lime Trees and Tree Flowers
Above the Fleabane and Golden Alexanders, Zizia aurea, is a canopy of tree leaves making a light shade in this part of the Wildlife Garden. I look up, we are standing in the shade of the small Basswood, Linden or Lime trees. The Lime trees are in full flower. The Lime blossoms smell sweet, and are a welcome source of nectar for Honeybees, butterflies and other pollinators. You can make a sweet tea (tila, tilleul) from the fragrant Lime tree flowers and leaves. And fun fact, Basswood or Lime timber is lightweight and soft, it is used for carving and making electric guitar bodies.

Lime tree in flower
June 2018

Early Summer Flowers
On the other side of the main path, under the River Birch trees, the yellow daisy-like Tickseed, Coreopsis is starting to bloom. Coreopsis spreads by roots rhizomatically, as well as feeding pollinators with nectar and pollen and producing seeds.
Tickweed, Coreopsis
Mary Van Dyke

Sundrops - Oenothera fruticosa
Arlington Central Library Wildlife Garden
Mary Van Dyke, June 2018

If you like splashes of yellow color in the garden, plant the showy Sundrops (Oenothera fruticosa), that blooms over the next few weeks to attract and feed moths, particularly Sphinx moths, bees, birds and hummingbirds.

Bee on Butterfly Weed - Asclepias tuberosa
Mary Van Dyke, 2018

The orange Butterfly Weed, Asclepias tuberosa, is in the Milkweed family, and is attractive to Honeybees, as well as some native bee pollinators. Milkweed seedpods are fun to open and look for the seeds. As highlighted in this video, a large community of various beetles and other insects, such as Monarch butterfly have co-evolved with milkweed plants. So look for beetles, as well as bees and butterflies on the Milkweed.
Milkweed Beetles
Mary Van Dyke
The Butterfly Weed, is now well-established in the Library Wildlife arden, and it self-sows. So each year, you can find Butterfly Weed plants growing in different places.

Midsummer Flowers, Coneflower, Rudbeckia, Bee Balm and Coral Honeysuckle
In the sunny section of the garden, the Purple Coneflower started to bloom this week. Coneflowers are native to the prairies, and grow well here too.
Coneflower with Bee
Mary Van Dyke
The Coneflower has noticeable external petals, that make an easy flat landing platform for beetles, bees and butterflies. Coneflowers are a composite flower. The Coneflower center, as in other composite flowers of the daisy family, including Rudbeckia and Dandelion, is made up of lots of different florets. Each of the many flowers in the center has nectar and pollen grains and are a favorite food for pollinators including bees, beetles and butterflies.
Monarch Butterfly on Sunflower with Rudbeckia below
Mary Van Dyke

Image result for bee balm with hummingbird
Ruby-throated Hummingbird visiting Bee Balm, Monarda didyma
photo by Larry Master
Bee Balm, Monarda didyma
Mary Van Dyke
Over the next few weeks, the Bee Balm, Monarda didyma, will be flowering. It is fragrant with scent of bergamot. Bee Balm has beautiful red flowers that we enjoy visually, that also attract hummingbirds and long-tongued bees to visit for the nectar rewards and to pollinate.
Central Library Wildlife Garden
View of Pergola, Coral Honeysuckle and Buttonbush
Garden Talk, June 2018
Mary Van Dyke
Central Library Wildlife Garden
Pergola, Coral Honeysuckle, Bee Balm and Buttonbush
June 2018
Mary  Van Dyke
On the pergola, I notice the red trumpet flowers of the Coral Honeysuckle (Lonicera sempervirens). Coral Honeysuckle is one of my favorite plants in the garden. It has a very long blooming time, and can flower in succession from March to October. The Coral Honeysuckle co-evolved with hummingbird pollination and produces nectar and pollen from about April 15th, when it is ready to be pollinated by the arrival of Ruby-throated Hummingbirds.  Coral Honeysuckle is the logo of the Plant NOVA Natives alliance, it is also the host plant for the Snowberry Clearwing moth that looks like a miniature hummingbird.
Coral Honeysuckle, Lonicera sempervirens
Mary Van Dyke

Plant NOVA Natives logo
with Coral Honeysuckle and Hemaris diffinis moth
Ruby-throated Hummingbird visiting Coral Honeysuckle
photo by Will Stuart

Late Summer Flowers
Between the pergola and the bike racks, the Buttonbush shrub (Cephalanthus occidentalis) is in bud. In a few weeks, the Buttonbush will be covered with flowers with nectar attractive to bees and butterflies.

Buttonbush flowers with bee
Mary Van Dyke

Tiger Swallowtail Butterfly drinking Buttonbush nectar
Mary Van Dyke

Obedient Plant and Carpenter Bees
Related image
Carpenter Bee on Obedient Plant
photo by Henry Hartley
Obedient Plant, Physostegia virginiana, flowers later in the season and is often pollinated by Carpenter Bees (Xylocopa virginica). Carpenter Bees have a short tongue and sometimes drill a hole in the back of the plant’s flower.  They are ‘nectar robbers’. Scientists studying blueberry pollination have found that 'nectar robbery' by Carpenter Bees may or may not impact pollination rates, given that another bee, such as a Honeybee may additionally pollinate through 'nectar thievery'. Sometimes you might find a Carpenter Bee asleep on a flower. The white-faced Carpenter Bee is the male. As with all bees, the male bees do not sting. The Carpenter Bee behavior can be annoying when they buzz around together in early spring or make holes, excavating a nesting site, in your deck or pergola. However the Carpenter Bee damage is rarely structural. The female bees do have a stinger (a modified ovipositor) but like most native bees, female Carpenter Bees do not use their stinger unless they are under severe attack or defending a nest.
Autumn Flowers and Pollinators
from Covering Ground, Mary Van Dyke, 2018

Visit the Library Wildlife Garden in the autumn to see the yellow Goldenrods (Solidago spp), purple Ironweed and Fall Asters in full flower. These flowers provide nectar and pollen for pollinators at the end of the season in September and early October, and are very important additions to extend the food sources for insects and birds in our garden.

Allergies and Pollen
Note that the flowering plants that have pollen that is often allergenic to humans: Oaks, Pines, Birch, Grasses, Ragweed are all wind-pollinated. These wind-pollinated plants produce lots of light wind-borne pollen to ensure their effective pollination and reproduction. The flowers in the garden that are pollinated by insects and other pollinators, have heavier grains of pollen that is usually non-allergenic to humans. In the fall, many people are allergic to Ragweed with its small wind-borne pollen. Fall-blooming Goldenrod, and spring blooming Golden Ragwort are pollinated by insect pollinators. Here’s some photos to help remember the differences and correctly identify Ragweed with its greenish flowers:
from Covering Ground, Mary Van Dyke, 2018
Winter Beauty - Leave the Stems and Seedheads in the Garden
For a gardener, wishing to support pollinators, rather than "tidying up the garden" it is better to leave the flower stems and seedheads in place over the winter. A lot of plants (such as Lobelia syphilitica) have hollows stems. Native bees will overwinter in the stems.  Another tip is to "tidy up" the garden in the spring, and as late as possible, for example in April rather than March.
Winter Beauty - Native Plant Sun Garden
at Green Spring Gardens
Mary Van Dyke, January 2018
Here at Green Spring Gardens, photographed in January, you notice that the sunny native garden beds are maintained in this way, leaving the flower stems and seedheads well into the spring before trimming back. Any stems cut in fall or early spring are left on site as “bee hotels”

Pollinators and Food Crops
After the Garden Talk and tour of the Central Library Wildlife Garden, I visit the Central Library’s Organic Vegetable Garden. I watch a bee or two visit the Buckwheat flowers.

Bee on Buckwheat Flowers
Mary Van Dyke

I am reminded, that “Pollination is critical for food production and human livelihoods, and directly links wild ecosystems with agricultural production systems” (from Biodiversity for a World Without Hunger).

In the global context:
  • 80% of all flowering plants are pollinated by animals (mainly insects)
  • Pollinators such as birds, bees and bats affect 35% of the world’s food production
  • “ At least one-third of the world’s agricultural crops depends upon pollination provided by insects and other animals”

What Can I do to Grow Community in My Garden?
  • Grow flowers for seasonal beauty and interest, and to provide food for more pollinators from early spring to late fall
  • Add locally-native plants that co-evolved with pollinators
  • If possible, don’t trim flower stems in the fall, leave as many seedheads as possible in place to overwinter, as the stems will likely will be sheltering bees and other insects
  • If you do cut flower stems, leave some stems on-site as “bee hotels”
  • Grow flowering plants to attract pollinators to food crops
  • Register your garden as a pollinator garden and "bee one in million" at
The Central Library Wildlife Garden is managed under Yu-hsin Hsu’s guidance with consultation with experts from Virginia Native Plant Society, Plant NOVA Natives, Arlington Regional Master Naturalists, and now hosts a thriving collection of over 50 native plant species. Come and visit this garden with its growing regional native plant collection, and find out what is blooming at different times of the year.

Thank you to Yu-shin Hsu and Laura Beaty for presenting this week’s Garden Talk at the Central Library Wildlife Garden. The Arlington Central Library Wildlife Garden and the Organic Vegetable Garden are open to the public all year round. If you would like to volunteer in the gardens, or have questions contact Adult Services Supervisor, Patricia West,

If you would like to know more and are interested in growing a garden for pollinators check out resources at:

Xerces Society -
The Pollinator Partnership -
Guide to Native Plants for Northern Virginia -
Video - Milkweed Co-evolution with Insects, Cornell
Video - The Hidden Beauty of Pollination Louis Schwartzberg, TED2011