Life History

Seeds can germinate from early spring to late fall, limited mainly by water. Seedlings establishing in early July or sooner can flower and produce seed by early fall, thus reproducing as annuals. Seedlings establishing in late July or later will remain as rosettes and produce flowers and seeds the following year, reproducing as winter annuals or biennials. Short-lived perennial reproduction was observed in plants that re-grew after alfalfa cutting. Rosettes, but not flowering plants, accumulate non-structural carbohydrates (sugars) in the roots until the first hard frost. These sugars are needed for winter hardiness, respiratory maintenance during dormancy, and growth following dormancy, and therefore rosettes generally survive winter, whereas flowering plants do not.

Hoary alyssum has low water requirements. In a study in Germany, germination and establishment were limited by the availability of open sites and water. However, once established, light was more important for growth and reproduction than water. In a Wisconsin alfalfa field, hoary alyssum did poorly where alfalfa was vigorous with a shading canopy, but thrived when alfalfa growth was poor. Similar to most mustard plants, hoary alyssum does not host arbuscular mycorrhizal (AM) fungi and had high mortality when grown experimentally in nitrogen-enriched soil and in the presence of adjacent plants inoculated with AM fungi.

Hoary alyssum reproduces only by seed. Flowers are insect pollinated, predominantly by small insects able to access the shallow nectaries in the small flowers, including syrphid and other flies (Diptera), wild bees, and wasps (Hymenoptera). Spring flowering plants are able to produce large numbers of seeds when grown in the open. In Minnesota, biomass production was 10 times greater, and seed production was 20 times greater from plants grown in open areas compared to vegetated areas. In North Dakota, seed production averaged 2,530 seeds per plant. Herbicide studies suggest hoary alyssum can form a persistent seed bank and seeds can remain dormant and viable for several years.

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Last Modified: 11/18/2008