Dandelions important for the garden ecosystem

Posted May 07, 2010, at 8:58 p.m.

The dandelions are blooming throughout Marjorie’s garden this week. On warm sunny mornings each of the dozens of flower heads lining the path from porch step to vegetable garden has one native bee, fat bumblebee or slender solitary bee, crawling slowly across a plane of bright yellow flowers, foraging for nectar and pollen. Later, in June and July, some of these same bees may be pollinating our tomatoes and cucumbers.

Most of the dandelion plants grow in places that we will mow every two weeks or so, but only after the dandelions have gone to seed. We want to keep dandelions around the garden because we value the pollinators that they attract, and I cringe whenever I see someone mowing them down when still in bloom. How many bees do those mower blades kill?

The bees need the dandelions as an early source of nectar and pollen, but the dandelions do not need the bees. They can reproduce by a process called apomixis, the seeds developing without pollination. Each new dandelion is thus genetically identical to the parent plant.

Dandelions brighten the early spring landscape. Together with the carpets of bluets that flower at the same time, dandelions turn otherwise uninspiring expanses of lawn into mosaics of color and texture.

Who can resist picking a dandelion clock, the term used for the head of single-seeded fruits, each attached to its own parachute, and blowing the seeds to the wind? So what if some of those seeds find their way into the strawberry bed? These you pop out of the ground as you wander around the garden on sunny April mornings, making grand plans for the season at hand.

And consider the impact of dandelions on garden biodiversity. A wide expanse of lawn, managed to exclude all weeds, has a biodiversity of one, the grass species. The chemicals used to control weeds (and insects) have further reduced surrounding biodiversity. On a small scale, such a lawn reminds me of another tiresome grass monoculture — the never-ending cornfields of Iowa.

The presence of dandelions in the lawn increases plant diversity by at least one species, insect diversity by the number of different nectar and pollen feeders, and other wildlife species diversity, including birds, through the absence of toxic chemicals.

Yes, I know, dandelions are not native to Maine, or North America for that matter, at least not the most regionally common species of dandelion, Taraxacum officinale. Native to Eurasia, this non-native species has followed humans around the world and can even be found in Alaska.

But is dandelion an invasive species? In Alaska’s Denali National Park, dandelions can be found in roadside ditches and cut banks, both human-disturbed areas, and there are concerned residents who would call them invasive. But experts there believe that dandelions do not have what it takes to move from those disturbed areas into wilder areas where they would outcompete native species for essential resources, the hallmark of an invasive species.

A recent publication by the Maine Organic Farmers and Gardeners Association, Bee-Friendly Farming Increases Crop Pollination, recommends dandelions for attracting native bees to the garden. Dandelions also are recommended by the University of Maine Cooperative Extension as an important pollinator plant in Maine (www.umext.maine.edu/onlinepubs/htmpubs/7153.htm). The list includes the statement, “No plants listed here are invasive exotic species.”

Wherever humans have roamed, dandelions have become naturalized in disturbed areas, like our front lawns, their seeds hitching rides on car tires and shoes. Let’s acknowledge which species is the true invasive species. Let’s appreciate dandelions for the service they provide in the garden ecosystem and for brightening the otherwise desolate landscapes in front of many homes.

Keep the lawn mower in the garage until dandelion seeds fill the air!

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