Gardening with Chip

Winter annual weeds in the vegetable garden and landscape beds

Annual plants go from seed to seed in less than one year, sometimes in periods as short as 45 days. Once they have thrown off their usually prodigious quantities of seed, the plants die. As you might suspect, there are lots of annual weeds since their growth habit fits with our gardening cycles. Annual weeds have sophisticated mechanisms to ensure good year-to-year seed survival.

Annual weeds can be found throughout the gardening year. There are winter annuals, summer annuals and, in our mild climate, some that can be found throughout the year. This is the time to think about winter annual weeds, including identifying which ones you have, how they will impact your garden, and what steps you can take to reduce them for early vegetable gardening.

Winter annuals germinate in late fall through early spring and go to seed in spring/early summer. Some common examples include little bittercress, several mustards, bedstraw, red dead nettle, oxalis, and common chickweed. Clearly, the cooler temperatures and lower light intensity of winter are not an obstacle to them. They prosper when other warm season competitive weeds and plants are absent. A few winter annuals, especially common groundsel, seem to germinate in flushes throughout the year in our climate, but most winter annuals disappear by mid-May. Here are the biographies of several winter annuals.

Little bittercress is in the mustard family. There are two species found here. Cardamine oligosperma is native to the Pacific Northwest. It is often called pop-weed for the plant's ability to eject seed from its upright pods on the stems more than 15 feet. It prefers moist soil and tolerates some shade. Fall emerging plants can overwinter unless the winter temperatures are quite cold with no snow cover. Spring started seedlings grow very fast and then produce their small, white flowers on the plant's tall floral stems. One plant can produce over 5,000 seeds that can germinate in two weeks. That can produce a bed of bitter cress quickly. Since it likes moist soil, the taproot is usually easy to pull. However, there can be so many to pull if it has gotten a running start on parts of your garden. There are differing views on whether bittercress leaves are edible. Fresh, they are intense and somewhat bitter, but a short boiling makes a more "domesticated" flavor. Still, you will never eat your way out of a bittercress explosion. Fall mulching landscape beds will significantly reduce bittercress populations. C. pensylvanica is hard to differentiate from C. oligosperma, but they both basically grow much the same.

Red deadnettle is in the mint family but has no relationship to stinging nettles. There are several species, Lamium purpureum and L. amplexcicaule, that are both common here and both originally came from Europe. Despite being from the mint family, they don't have any classic mint flavor or a perennial growth life cycle. They do have characteristic square mint stems. Red deadnettle can form temporary ground covers and do support quite a few bee family species when they flower on upright stems in the spring and into summer. The biggest challenge for gardeners removing them by tillage or hand before you want to plant seeds is the space that they occupy. They don't pull out easily, and they can break off with remnants likely to come pushing back as your seeds start to emerge. Tarping an area so that no sun can get through can, if done by early February, should significantly subdue their ability to compete with your seeded garden rows you plant in 60 days or more. This is also true for most of the winter annuals. Red deadnettle had quite a few medicinal uses historically and is still sometimes used to reduce itching skin and help heal surface skin wounds.

Common chickweed (Stellaria media)is the last winter annual topic for today. Chickweed also came to North America with European settlers. Chickweed seeds usually start germinating in the fall, throughout winter, and into spring, unless winter temperatures fall to the low teens. The plant grows flattened to the ground and can form extensive covers over gardens, small caliper gravel piles, and other semi to full sun spaces. Chickweed produces lots of seeds. The plant is very popular with birds for its seeds and foliage. For that reason, some gardeners tolerate the plant until spring vegetable planting is starting. It does "till under" well when the soil is dry enough to till. Chickweed seed germination rates slow as the soil gets warm in the late spring to early summer. Chickweed is widely consumed in many parts of the world. For early planting in a chickweed populated area, it makes sense to cover the space soon with dark tarps or heavy dark plastic to reduce chickweed competition with your early spring seed plantings. If you are using transplants instead of direct seedings for your early crop, simple tillage or hoeing to reduce the chickweed competition will work if you keep ahead of any chickweed re-growth.

Take excess produce to the food bank, senior centers, or community meals programs. Cash donations to buy food for the food banks are also greatly appreciated. Sign up for Gardener training in either county.

Very helpful information sources are your local Extension offices. The Columbia County Extension is 503-397-3462, the Wahkiakum County Extension is 360-795-3278, and the Cowlitz County Extension is 360-577-3014. The Extension Service offices offer their programs and materials equally to all people.

Advice on future garden topics is always welcome by emailing me at chip.bubl@orgeonstate.edu.