Published by Brian Wagner on 10/24/25 in “Growing Flowers from Seed.”
Hesperis matronalis (commonly known as sweet rocket or dame’s rocket) is a mustard family (Brassicacae) biennial species native to mainland Europe. It usually behaves as a biennial, although it may last a third season in milder climates. Its flowers are lavender or white and it grows 3 to 5 feet tall with its four-petal, fragrant flowers. The flowers are similar to Phlox except they have four petals (not five). At dusk it has a singular fragrance like clove and lilac (sweet and a little spicy).
Seeds are quite easy to grow from seed – and the plants, while short-lived, can be planted in late autumn for a large splash of spring colour. They will likely die after flowering, similar to its cousin species Lunaria annua (Honesty), but they are a wonderful companion in the cottage garden. They can be somewhat invasive in certain areas, and it’s always good to deadhead spent flowers. I wouldn’t classify them as ‘invasive’ most of the time. There certainly isn’t much published research on this species, which reveals how minor of an invasive species they are (i.e., very invasive weeds get researched heavily). Also, the seed heads are very slow to produce seeds and can be easily removed before they disperse seeds.
Growing from Seed
Sweet Rocket is an interesting species to grow from seed. After seeds are harvested, they are conditionally dormant for the first 3 to 6 months. They will only germinate at very warm temperatures, around 25C (80F) to 30C (85F) in either light or darkness. They will not germinate at cooler temperatures. If you have freshly harvested seeds and want to sow them in late summer, this will be your best strategy.
However, the seeds have a non-deep physiological dormancy where they will exhibit cycling between dormancy and non-dormancy through the seasons, and if they experience temperatures at high heat for a while, they will get pushed into dormancy. A very hot summer will push them into this so-called secondary dormancy. To get them out of this, you will need to cold stratify the seeds for 4 weeks at 4C (40F), and then you must sow them at 21C (70F); they should germinate within a week. Light is not required, but it won’t hurt.
If you keep seeds for a year or longer at room temperature (dry storage), they will germinate just fine at 21C (70F) and in light, and they will pop up in a few days. This is because seeds have after-ripened after 12 months of dry storage, relieving them of their primary dormancy. But, don’t crank the heat – keep it cool, under 21C (70F) or else they might get pushed into secondary dormancy again (and requiring cold strat). You need to keep the seeds at room temperature and dry for at least 12 months to germinate them in this way – and even 6 months is not enough time. There is a wonderful study published by Susko and Hussein (2008) if you’re interested in the science of this mustard jewel.
References
Baskin CC, Baskin JM. Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Second Edition. 2014. Academic Press: San Diego, California
Correa L, Steinbauer GP, Grigsby B, Correa L, Frank P. A study of methods for obtaining laboratory germination of certain weed seeds. InProceedings of the Association of Official Seed Analysts 1955 Jan 1 (Vol. 45, pp. 48-52). Association of Official Seed Analysts.
Deno N. Seed Germination Theory and Practice. Second Edition. 1993. Self-Published. Available online by the United States Department of Agriculture at http://naldc.nal.usda.gov/catalog/41278
Susko DJ, Hussein Y. Factors affecting germination and emergence of dame’s rocket (Hesperis matronalis). Weed Science. 2008 Jun;56(3):389-93.
Yücel E, Duran A, Türe C, Böcük H, Özaydın B. Effects of different salt NaCl, nitrate KNO3 and acid HCl and H2S04 concentrations on the germination of some Hesperis species seeds. Biological Diversity and Conservation. 2008;1(2):91-104.