Gardeners love double flowers. And why not? With their dense flowers jam-packed with petals, they really do stand out from the crowd. Moreover, double flowers are generally sterile or nearly sterile. Since they aren’t pollinated, they quite often remain open longer than single flowers, another advantage for the home gardener.
For insect pollinators, though—bees, hoverflies, butterflies, etc. —, double flowers are bad news.
Most of the time, the mutation that leads to double flowers converts stamens into petals. But in the wild, the stamen—typically a filament with a yellow anther—has a role to play. It provides pollen… exactly what many pollinators come to look for in a flower. Indeed, many pollinators depend entirely on pollen as a food source. To them, double flowers are a disaster: there is no pollen… or at least, there is less. (Some double flowers still have at least a few functional stamens, but often they are hidden by too many petals and difficult to access.)
When it comes to those creatures that come to flowers to looking for nectar, as is the case with butterflies, long-horned bees and hummingbirds, the situation is little better. The flower’s nectaries (organs that produce nectar) are generally found at the very base of the flower… therefore hidden by all those dense petals. As a result, access to the nectaries is difficult and sometimes impossible. So, double flowers are not a good source of nectar either.
With so many pollinators in dire straits, especially among bees, whose populations are collapsing worldwide, double flowers would appear to be yet another nail in their coffin.
A Waste of Time and Energy
Very often, pollinators continue to visit double flowers even if they can’t feed on them. That’s because the flower continues to signal to them, due to its color or odor, that it’s ready for a bit of pollination, yet when the insect visits and tries pushing the petals aside, it finds nothing to eat. You’d think the bug would be intelligent enough to learn from that experience and move to another plant. Indeed, some pollinators do have that kind of smarts, but others just never seem to learn from their bad experiences. So they go from flower to flower on the same pollenless, nectarless plant, wasting their energy, until they finally find flowers on a nearby plant where pollen and/or nectar are accessible.
Semi-double flowers are intermediate between single flowers and double flowers: only some of the stamens have been converted into petals. Depending on the variety, they may produce as much pollen and nectar as a single flower or less, and their anthers and nectaries may be easy to reach or not readily accessible. Usually, if you can clearly see yellow anthers in the center of a flower, it will be suitable for pollinators.
No Need to Panic
If your flower bed is composed only of double flowers, it really would be a disaster for pollinators, but that’s rarely the case.
The typical flower bed usually contains a wide variety of plants, many with single flowers. In fact, in most gardens, there are many more single flowers than double ones. Also, the concentration of blooms in a flower bed is much greater than it would be in the wild (or in a lawn!). As a result, flower beds are such a popular and reliable source of food for pollinators that many are willing to travel long distances to visit, sometimes even several kilometers.
And besides, don’t think that only domesticated flowers attract pollinators without giving them their due. Nature is full of flowers that lure insects with promises of pollen and nectar, but don’t deliver the goods. Many orchids, in particular, are specialists in visual, olfactory and sexual lures: they promise the world and organize things so they ensure their own pollination, but the insect still leaves empty-handed.
In Your Garden
Most home gardeners are rendering a service to threatened pollinators simply by putting in a flower bed, but if you specialize in plants renowned for their double flowers (peonies, roses, carnations, camellias, etc.), it would be nice of you to include a fair share of “simpler” flowers (ones with yellow stamens visible) to the mix to support your friends, the pollinators.