Drive down any of Ontario’s highways in early July, and it is hard not to notice the bright yellow blooms of Birdsfoot Trefoil (Lotus corniculatus.)
In Sarnia, our prettiest Birdsfoot Trefoil crop can be found in the two not-yet-developed patches of grass south of the Walmart parking lot, next to LCBO.
Birdsfoot Trefoil is so named because once the flowers fall, the remaining seed pods look like bird’s feet. The perennial plant has sulfur yellow blooms rising above small green foliage with tough, wiry stems.
Birdsfoot Trefoil is listed as an invasive species in many jurisdictions, primarily south of the border, where it invades grasslands that are home to many native plants. In Ontario it gets mixed reviews. Trefoil has several benefits, and has often been used as green manure cover crop in agriculture, ploughed under to add valuable soil nutrients.
Trefoil was introduced to North America from Europe with good intentions. It served as a nutrient rich forage for animals, and, as a member of the Pea family, it hosts bacteria that fixes nitrogen, serving to raise soil fertility.
Nature lovers appreciate Trefoil for their bright yellow blooms, which are often a hive of activity for pollen-seeking bees.
On the other side of the coin, Trefoil grows where little else grows, and once established, can inhibit the growth of valuable native plants. Although not as invasive as Phragmites, Purple Loosestrife, or Queen Ann’s Lace, we would do well to keep an eye on Trefoil’s aggressive path.
Trefoil manages to grow in the poorest of soils because its roots, which are difficult to pull, go deep in search of moisture. It needs no fertilizer because it creates its own nitrogen. Trefoil is often the first weed to grow at the edge of a gravel highway.
Trefoil can be a lawn weed, particularly in lawns that are poorly cared for and under fertilized. It likes draught and sunshine, although can survive in damp soil. Since Trefoil needs sun, the weed will not be found in the forest.
Along the highway, Birdsfoot Trefoil miserly enjoys the company of several other non-native weeds. In the past, Crown vetch was planted by the Department of Highways as a soil stabilizer to grow on slopes and prevent erosion. Knapweed, listed as an invasive species, has pale purple flowers, growing in neglected areas with poor soil.
Ontario’s worst offender is Phragmites, the tall growing grass-like weed that likes to grow in ditches and wherever it can find moisture. Like a bulldozer, Phragmites continues to expand in neglected areas, with no regard for any plants in its wake.
Once established, invasive weeds growing along the edge of roadways are difficult to get rid of. Controlled burning will set the weeds back but will not eliminate them. Herbicides will prove effective, but there is general reluctance to apply weed killer unless necessary. Planting wildflowers with the hopes they might outperform non-native plants has been largely unsuccessful because native plants prefer to grow in native environments.
