By Laura Gardner, Master Gardener

At this time of year there are two kinds of easily identifiable weeds: “winter annuals” and “biennials.” Biennials begin their lifecycle by germinating from seed in the first growing season. Winter annuals germinate from seed in the fall. They both form a vegetative basal rosette that lies in a suspended state over winter. The rosette protects what is known as the shoot apical meristem—stem cells of the plant that are responsible for the generation of shoots and leaves later in the spring. They will then grow more upright, flower, produce seeds, and then die, finishing their lifecycle. Some species may function as either a winter annual or a summer annual. Summer annuals germinate from seed in the spring and complete their life cycle that same year. One of the challenges of managing summer annuals is that they can reproduce more than once a year, potentially contributing to a large seed bank. Biennials generally take two years to complete their lifecycles. However, some so called biennial species may extend into subsequent growing seasons and be more like perennials if they have sufficient root energy stores and have not had the opportunity to flower and go to seed. This can happen if you do not remove at least the root crown of the plant when weeding.

In the Peterborough Public Library’s native plant garden, I took some photographs of some basal rosettes with the idea of identifying them later at home. Coincidentally, a copy of a book that I had on order for more than a year finally arrived: Weeds of the Northeast, 2nd Edition, by Joseph C. Neal et al. (Cornell University Press). In addition to the US Northeastern, Mid-Atlantic, and Upper Midwestern states, the book includes Southern Canada. In the 26 years since the first edition was published in 1997, more than 200 new species have been added. Many of these new species are invasive plants from the horticultural trade [e.g. Common Periwinkle (Vinca minor)]. It is strictly an identification guide and so if you are looking for weed management guidance, this type of information will need to be found elsewhere.

The book has a dichotomous key that is a bit different from others. It relies on identifying the plants through their vegetative parts such as leaf lobes, leaf arrangement, leaf margins, leaf hairs, etc., but not on their floral traits. It also does not lead you to an immediate single species identification, but rather enables you to compare your plant with several possible matches through their photos and descriptions. The photos are particularly valuable for identification purposes—showing plants in various stages of life—from seedling to maturity. The glossary is helpful for those that are unfamiliar with some of the botanical terms. This is a great resource for anyone to use to confirm the findings of a plant identification app.

Here are some of the weeds I found and identified using this guidebook:

Shepherd’s Purse (Capsella bursa-pastoris): A summer or winter annual.

Field Pennycress (Thlaspi arvense): A Summer or Winter Annual

Canada Horseweed (Erigeron canadensis): Summer or Winter Annual

Bull Thistle (Cirsium vulgare) and Common Mullein (Verbascum thapsus): Biennials