One of the early-summer bloomers lighting the garden right now is Sweet Rocket (Hesperis matronalis). Sweet Rocket is a common old-fashioned garden plant that is known by many names. According to Wikipedia, these include Dame’s Rocket, Damask Violet, Dame’s Violet, Dames-wort, Dame’s Gilliflower, Night Scented Gilliflower, Queen’s Gilliflower, Rogue’s Gilliflower, Summer Lilac, Sweet Rocket, Mother-of-the-evening and Winter Gilliflower. The genus name, Hesperis, is Greek for evening, and was probably chosen because the scent of the flowers becomes more conspicuous towards evening. I can’t vouch for this personally, however, because the mosquitos that appear in swarms in the evening discourage lingering for flower sniffing.
Sweet Rocket was probably introduced to North America from its native Europe in the 17th century and has since made itself right at home on its adopted continent. It is a prolific seed producer and can now be found along ditches and woodland edges over a wide range. The plant pictured here was already in the garden before I arrived and I have to admit that I didn’t recognize it at first. Like many others, I initially mistook the plant for a variety of phlox, but upon closer examination, it is easy to tell the two apart. Sweet Rocket is a member of the mustard family, and like all mustards, the flowers have four petals rather than five as does phlox. If you look closely, mustard flowers also feature 6 stamens, 4 tall and 2 short.
As these photographs show, the Sweet Rocket flowers are appreciated by pollinators such as the Tiger Swallowtail butterfly and bumblebee shown above. However, if it weren’t already here, Sweet Rocket isn’t a plant I would chose to add to the garden because it is considered an invasive species. The Ontario Exotic Species Ranking system has four categories, and Sweet Rocket is placed in Category 1 with the worst offenders. Category 1 plants are described this way:
Aggressive invasive exotic species that can dominate a site to exclude all other species and remain dominant on the site indefinitely. These are a threat to natural areas wherever they occur because they can reproduce by means that allow them to move long distances. Many of these are dispersed by birds, wind, water, or vegetative reproduction. These are the top priority for control, but control may be difficult. Eradication may be the only option for long-term success.
Sure enough, a quick look along the river banks and roadsides reveals plenty of escapees. Given the highly-disrupted agricultural landscape around here, it’s probably not a big issue in this area, but invasiveness is certainly an important feature to keep in mind when planning a garden. For a list of the four categories of invasive plants to avoid, check out the Invasive Exotic Species Ranking for Southern Ontario. Another excellent source of information is the Ontario Invasive Plant Council site, which features a guide to alternatives to invasive species that are often planted in gardens. Follow this link to Grow Me Instead!