Hesperis is an herbaceous flowering perennial or biennial belonging to the Brassicaceae, or mustard, family of plants. The most familiar species, Hesperis matronalis, is commonly known as Dame’s Rocket or Sweet Rocket. Native to Europe and Asia, it has naturalized over the years in much of North America, where it is now considered an invasive weed in many states. Though there are more than 60 species other than Hesperis matronalis, they are fairly obscure and not easily found. Hesperis matronalis is the only variety that is generally known and widely available.
The flowers of this plant bloom in shades of purple or white and grow on showy, extremely fragrant racemes, or stems on which flowers start at the base and add new blooms as the shoot grows. Their scent gets stronger at night, hence the name hesperis, which means evening in Greek. Plants are usually quite tall, reaching up to 5 feet (1.524 meters) with proper growing conditions.
These plants usually won't survive in hot, humid climates, preferring at least partial shade and moist soil. Hesperis loves damp thickets and wooded areas and is often seen growing along streams and riverbeds. They are frequently planted in wildflower gardens and are an addition to many mixed wildflower seed packets.
Some caution is needed when growing hesperis, which can spread and overtake a garden within a few years. Hesperis left to multiply can crowd out less aggressive plants. This can be avoided by removing the dead flower stalks promptly, before they set seeds.
Wild hesperis has become a problem in many areas. It has overtaken many fields and roadsides in the northeastern United States, and the flowers can be seen blooming by the thousands in early summer. It is a beautiful sight that, nonetheless, has caused the plant to be listed in many areas as invasive and not to be cultivated.
Seed makes it easy for those who wish to grow hesperis in their gardens to do so. Germination can take up to four weeks, so it should be started indoors several weeks before the last winter frost in cold areas. Seeds need light to sprout and should be left on the surface of the soil. Plants started early enough will flower the first year, though most won't bloom until the second year.
Hesperis is frequently confused with phlox. They look similar but have several differences. Phlox has five-petaled flowers and smooth leaves that grow parallel to each other, while hesperis flowers have four petals and hairy leaves that alternate on the stem. Hesperis also tends to bloom earlier in the summer.