While weeding the other day, I had the welcome distraction of a fat bumblebee foraging nearby for nectar and pollen. Among the sea of blue violets that is my lawn, the bee zipped from flower to flower, as bees do. Anytime it landed on a violet, the weight of the bee pulled the flowerhead to the ground. Nonetheless, the bee popped right back up. Trying the next violet, it attempted over and again to gain footing on the flower petals and never succeeded.
Both bumblebee and wildflower are native to my region. But common blue violet (Viola sororia) are not a food source for bumblebees. This viola’s preferred pollinator is the Violet Miner bee (Adrena violae), whose simple 5-petal flowers with short nectar spurs on delicate stems are specialized for them. Where bumblebees are too plump, slender bees, like mason and sweat bees, easily gain access to common blue violet nectar.
Specialist flowers like violas have complex reproductive structures adapted to specific types of pollinators. Limiting access to certain insects is nature’s way of supporting a balanced and biodiverse ecosystem. Alas, the bumblebee would’ve had better luck with a generalist flower, like those from the Aster family.
It’s a telling reminder that a flower is not a flower to all bees.
The whole episode got me thinking about the flowers we grow and whether they serve the wider community of pollinating insects.
What we choose to grow in our gardens can have an enormous impact on bees, butterflies, moths, and other pollinators. These insects are facing multiple threats in habitat loss, pesticide use, pollution, and extreme weather due to the climate crisis.
The popularity of pollinator gardens shows that people really do care about protecting these hard-working creatures. These days, many plant nurseries have whole sections dedicated to pollinator-friendly plants, which would have been unimaginable a decade ago. Yet even with this progress, garden centers typically only sell cultivars and hybrids. Some have been bred so extensively that they bear little resemblance to the original plant.
Cultivars are beautiful, but may not be very useful to our bees and butterflies. And despite our best intentions, we may unwittingly be planting flowers that have little to no value for pollinators.
What is a Cultivar?
Since humans began growing plants, we have changed them to suit our needs. Corn is an example of a cultivar. It is a plant that doesn’t exist in nature. It began as a wild grass called teosinte with 5 to 10 hard-shelled kernels per ear. Teosinte grains look nothing like the corn we have today, averaging 800 juicy sweet yellow kernels per cob.
Cultivars are created through selective breeding, as with corn, by crossing two different species to make hybrids. First-generation (F1) hybrids are crossed with the original parents, and then the resulting seeds are exposed to radiation or chemicals to alter plant DNA.
(You can tell a plant is a cultivar when the label includes a name in single quotes, such as Lobelia cardinalis ‘Black Truffle’, sometimes followed by a patent number. Hybrids are denoted by an × between species crossed, like Schlumbergera × buckleyi.)
Plant breeding practices are responsible for growing larger, sweeter, tastier, disease-resistant fruits and vegetables with much greater yields than would be found in nature. It’s also been a boon for producing enormous, breathtaking flowers.
Ornamental cultivars and hybrids are usually larger and more vibrant, come stuffed with lots of petals and in a rainbow of colors not typical to the species. But through the breeding process, critical flower parts tend to get sacrificed to produce such spectacular blooms.
Why Some Flower Cultivars Aren’t Appealing to Bees
Certain flower cultivars have been crossed and re-crossed for decades, and every horticultural modification removes the plant further from the wild species. Changing the shape, size, color, and function of flowers also disrupts the morphological match between flower and insect that coevolved together over hundreds of millions of years.
A typical flower consists of four main parts:
- The petals, often colorful to attract pollinators
- The sepals, for protecting the developing bud
- The stamens, composed of pollen-producing anthers and filaments
- The pistil, containing the stigma, style, and ovary where fertilization occurs and seeds are produced
Flowers are the reproductive organs of plants. The color, fragrance, and availability of nectar are all designed specifically to attract pollinators.
In most flowers, the petals form an outer ring around the center, with the (male) stamens circling around the (female) pistil. Pollinators drink from the nectaries located at the base of the stamens or collect pollen from the anthers. As they travel from flower to flower, insects transfer the flower’s genetic material (pollen) from stamens to pistil. When fertilization is successful, the plant can start producing seeds to grow more plants.
Heavily bred and hybridized flowers have undergone such dramatic changes that they are more likely to be inaccessible to bees.
Double Flowers
There’s no question that people love full and fluffy double flowers. The more petals, the better. But they come at the cost of the reproductive parts, which are replaced to make room for the extra petals.
Double flowering mutations occur spontaneously in nature anytime a plant mistakenly develops additional petals where the stamens ought to be. Plant breeders will select for this trait and, over several generations, develop fully double flowers that are so stuffed with petals that the stamens and pistil have been completely removed. Without pollen, the cultivar is sterile and produces no seeds, and this has downstream effects on seed-eating creatures like birds.
Some double cultivars still have their stamens and pistil, but there’s such a profusion of petals that there is no opening for bees to access the nectar and pollen.
Diminished Nectar and Pollen
Even when a flower center isn’t completely obstructed with extra petals, the nectar and pollen-producing abilities of some flower cultivars have been reduced or eliminated entirely.
In developing the perfect flower for size, color, disease resistance, shade tolerance and beyond, sometimes the primary function of flowers – as food for bees and butterflies – gets lost in plant breeding. Flowers might have lower quantity or quality of nectar or pollen, if any at all.
Hybrids and cultivars may still produce abundant floral rewards for pollinators, but the pollen and nectar might be less nutritious. Some sampled cultivars proved to have less than 20% of the nectar sugar content than the straight species. Or sometimes the pollen can be so low in amino acids that bees are forced to discard it when it gets refused by nurse bees back at the hive.
That’s all to say, foraging for poor quality nectar and pollen is a terrible waste of time and energy for our bees.
Unusual Colors and Scentless Flowers
Bees have an exceptional sense of sight and smell, finely tuned for locating a feast of flowers.
But – bees can’t see the color red. They can only see yellow and orange, blue-greens, blue, violet, and “bee’s purple”, a combination of yellow and ultraviolet light. Bees are most attracted to purple, violet, and blue flowers. So when a flower that was originally purple has been bred into a flashy red, for instance, it would go unseen by bees.
Another helpful trait for bees and other pollinators find food in flowers is by scent, but this too can be erased through the flower breeding process. The loss of floral fragrance makes it all the more challenging for bees to discover the nectar source, and might fly right on by it.
6 Flowers Bees Can’t Use
Here are some examples of popular garden flowers that have been so intensely bred for beauty that they are no longer a good food source for bees:
1. Garden Pansy
I hate to include garden pansy (Viola × wittrockiana) on this list – it’s one of my favorites and their happy little faces never cease to make me smile! But as far as wild life value goes, pansies aren’t very useful for bees.
With larger blooms in every color imaginable, garden pansies have a longer nectar tube (known as a spur) than its forebear wild pansy (Viola tricolor). The spur is too long for Viola specialists and small bees with short tongues to reach. Long-tongued bees, like bumblebees, can’t access pansy nectar either. They are too heavy to get a good grasp of the petals and fall off the flower.
Although the sugary liquid can’t be accessed by bees, garden pansies achieve pollination with the help of pollen beetles and ants.
2. Petunias
Petunias (Petunia x hybrida)are incredibly popular bedding, container, and basket plants, loved for the variously colored and patterned funnel-shaped flowers that bloom freely to frost. Despite the long blooming window, have you ever noticed that petunias never seem to attract many pollinators? The reason is hybrid petunias have very little nectar.
According to a British field study, both multiflora and grandiflora petunias had remarkably few visits from bees. With plenty of flowers in bloom (1200 in the single flower multiflora; 540 in the single grandiflora; 44 in the double flower grandiflora), only 3 bees were observed foraging the petunia flowers over the course of a day. Not a single one was interested in the double cultivar.
3. Hybrid Tea Rose
It’s too easy to become entranced while gazing at a fully double tea rose (Rosa x hybrida) and its undulating swirls of soft velvety petals. But when you can’t see a protrusion of stamens and pistil spilling out from the center of the rose, bees won’t be able use it.
If you want to plant a few rose varieties for the bees, old garden roses and wild roses have an open floral disk that pollinators can access.
4. Double Peony
Garden peony (Paeonia lactiflora) was originally a much simple flower, large and cup shaped with 5 to 10 petals arrayed around a center teeming with yellow stamens. After 2,000 years of cultivation, peonies look a lot different today – particularly double cultivars like ‘Sarah Bernhardt’ and ‘Kansas’.
Double peony cultivars are so densely arrayed with petals that the yellow center is completely obstructed. If there is any pollen or nectar to be had, it’s hidden away under the petals.
5. Begonia
Tuberous begonia (Begonia × tuberhybrida) was first hybridized in the Victoria era and since then thousands of cultivars have been created. Many varieties have fully double flowers that, as you might’ve guessed, don’t harbor any sustenance for our local bees.
Similarly, other Begonias with more open-faced flowers, like Semperflorens, Trailing, and Elatior types, house almost zero nectar and pollen.
6. Double Coneflower
Coneflowers (Echinacea spp.) are a must in pollinator gardens – attractive, long-blooming, and a significant food source for bees, butterflies, and songbirds. Since the 1960s, major efforts to have been underway to improve the look of coneflowers and now there are more than 100 cultivars gracing retailer shelves today.
When choosing a coneflower for the bees, not just any Echinacea variety will do. Double cultivars, like ‘Pink Double Delight’, ‘Secret Desire’, and ‘Puff Vanilla’ have heavily modified flowerheads. Where normally the dome center is filled with tiny orangish-brown florets, in double coneflower these are remade into a pompon of fluffy petals.
Nativars (cultivars of native species) are growing in popularity. Although there are some exceptions, bees will usually choose the wild type over the cultivar.
So…what if your most cherished flowers aren’t so great for pollinators?
There’s no need to be a purist – I’ll certainly be keeping my pansies (‘cuz I love them), but I’ll also balance it out by planting even more beautiful and useful flowers.
It’s not so much the presence of cultivars in gardens that’s the problem; it’s the absence of natives. When your gardening goals include supporting pollinating insects, the simplest way to help is by planting more flowers native to your region. The straight species are the ones that the local bees will find easily and the open flowers will provide a high quality source of nectar and pollen.
Given the popularity of cultivars and hybrids, it can sometimes be difficult to source non-cultivars from the usual places. But native plant suppliers are out there. If you’re in the Midwest, for instance, Prairie Moon is excellent for wild genotype native species.
Natives are best, but non-native flowers have a lot of value for bees, too. Zinnia, lavender, cosmos, and many small-flowered herbs are pollinator magnets no matter where you live. Use them to supplement the bee diet while you go ahead and revel in those frilly double blooms.
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