Reprinted from UMASS Extension Garden Clippings 2018, Vol 37:8. Article by Randy Prostak, UMass Extension Weed Specialist

As the end of the gardening season grows near, gardeners often let their guard down. This unfortunately can have consequences for their gardens and landscapes, as some weeds are still very active.

As the season closes, it is wise to shift your focus to weeds with a winter annual life cycle. Winter annual weeds germinate in late summer and fall. They grow vegetatively and then go dormant with the arrival of cold weather. In the spring, they continue to grow vegetatively early and then switch to a reproductive phrase during which they flower and produce seed. After flowering, they die with the onset of warm weather. I often refer to winter annual weeds as the “forgotten life cycle” because they appear at a time of the year when we may not be paying attention. Winter annual weeds can be just as problematic and troublesome as summer annual weeds.

Common winter annual weeds in the landscape, lawn and garden (photos of these winter annuals can be viewed at http://extension.umass.edu/landscape/weed-herbarium)
mouse-ear cress (Arabidopsis thaliana)
thymeleaf sandwort (Arenaria serpyllifolia)
downy brome (Bromus tectorum)
shepherd’s-purse (Capsella bursa-pastoris)
bittercress (Cardamine hirsuta)
sticky chickweed (Cerastium viscosum)
horseweed (Conyza canadensis)
spring whitlowgrass (Draba verna)
henbit (Lamium amplexicaule)
red deadnettle (Lamium purpureum)
field pepperweed (Lepidium campestre)
Virginia pepperweed (Lepidium virginicum)
pineappleweed (Matricaria matricariodes)
annual bluegrass (Poa annua)
knawel (Scleranthus annuus)
common chickweed (Stellaria media)
field pennycress (Thlaspi arvense)
corn speedwell (Veronica arvensis)
purslane speedwell (Veronica peregrina)

Winter annual weed management options

Landscape: Apply a fresh, thin layer (about one inch) of landscape mulch in very late summer or early fall to prevent winter annual weeds from establishing themselves. Weeds that have germinated and are very small can be smothered by mulching. Larger weeds can to treated with a glyphosate-based product as a direct spray. Non-chemical products containing clove oil, citric acid, acetic acid, or orange extract can also be used as a directed-spray to control winter annual weeds. Larger weeds occurring mid- to late fall can be physically removed by hand pulling.

Vegetable garden: After fall garden cleanup is done, consider sowing a cover crop of winter rye or oats. These grasses will compete with any winter annual weeds; the cover crop can then be tilled in the follow spring. Cover crops will also prevent water/winter erosion and over time will build soil organic matter.

Photo of Pineappleweed. Credit: UMASS Extension Weed Herbarium