Let’s take a look at some of the more common fall and winter weeds and what we can do about controlling them as best we can. Winter annuals (plants that go through their entire life cycle in one season) normally germinate in the fall or early winter and flower and produce seed by early summer.
Common types: annual bluegrass, annual ryegrass, annual sowthistle, common chickweed, common groundsel, clover, and plantain.
Most annuals can be controlled in the landscape with an integrated program of mulching, hoeing, hand-weeding, or spot application of an herbicide. If herbicide is used is used, winter annuals may be controlled by a preemergent herbicide applied during fall and a contact or translocated herbicide applied during winter.
1) Annual Bluegrass
Poa annua is a winter annual adapted to cool, moist sites, however it can grow an time of year in coastal areas, especially in shady, moist areas. It grows 3 to 12 inches at maturity. Its flower heads are branched with clusters of 3 to 6 flowers at the tip of each branch.
In ornamental plantings bluegrass can form dense patches that are aesthetically distracting, but probably have little detrimental effect on established shrubs and trees.
Annual bluegrass reproduces by seed and can have many generations in a season.
Control: mulching, hoeing, hand-weeding, or spot application of an herbicide.
Annual bluegrass seedling
Mature annual bluegrass
2) Annual Ryegrass
Annual ryegrass (Festuca perennis) is a cool season well adapted to sunny conditions and moderate temperatures.
It is often sown at high rates to overseed warm season turfgrass for fall, winter, and early spring color. It is not otherwise used for turf. Annual ryegrass dies in the late spring to early summer. It often turns yellow and dies before warm season grasses come out of dormancy.
Mature annual ryegrass
Plant structure of annual ryegrass
Plantain (Plantago major & Plantago lanceolata) is a common weed in year round. Both types have a fairly weak root system, however they grown from the base and mowing will not kill them.
Plantain commonly grows in turfgrass and their seeds and vegetative structures will contaminate equipment.
Remove plantains as early as you can, before they seed. Once you see a plantain in a spot, make sure to keep and eye on that area even after removal. Resprouting is common. Plantain control requires diligence over a period of time.
Chickweed (Stellaria media) is common in lawns during the winter. The mature plant can grow like a mat on the ground, covering a small area like a carpet. It reproduces mostly from seed, but it can also reproduce from creeping stems. Control should rely on hand weeding, hoeing, mulch, and solarization (if needed). It should be controlled before it flowers. It is important to not only remove the plant from the ground, but also remove it from the site, as it can reroot from the stem in moist areas. Proper water management is key as well, as this plant does not thrive in drier areas. Deep, infrequent watering discourages chickweed, including in lawns.
Chickweed flowers on a mature specimen
Common groundsel (Senecio vulgaris) is most common during cool, moist periods. Areas of over watering promote their growth during winter. They are toxic for humans and animals, over long periods of time or in large quantities.
They reproduce by seed. Proper water management and spot control (shallow hoeing and hand pulling), especially before they flower, help to control their spread. Mulch can also be very effective in control.
There are multiple types of common clover, and they tend cause problems in turfgrass. They can attract bees to their flowers, which is not a bad thing in and of itself, but cause problems for people playing on the lawn. Clover also diminishes the uniformity of lawns, and the mature burs of the burclover can become stuck on people’s clothes, or hurt them is they are walking barefoot.
Clover can be controlled by hand pulling, hoeing, and mulch for planter areas. Their seeds have a hard cover, and they can germinate over many years, so control will be an ongoing effort. Lawn areas are more difficult to control clover. Increasing the nitrogen and having less phosphorus in turf can help. The best defense against clover is a thick lawn. Mowing will not control clover. Hand pulling before the clover seeds are formed. Hand pulling will need to be done repeatedly. Mulch layers need to be around 4’’ thick to effectively control clover in planters.
A grouping of white clover
Annual sowthistle (Sonchus oleraceaus) can have pests that damage nearby plants, and can look like dandelion.
It germinates in the top ½ inch of soil, so cultivation or solarization before planting can provide control. Mulching is also commonly effective against this plant, however spot treatment (hoeing and hand pulling) will be required.
Because the seeds are easily dispersed by wind, these weeds often germinate in decaying organic mulch.
Whether it’s removing weeds and cleaning up your existing landscape or installing a new landscape, Creative Concepts Landscape will happily discuss possibilities with you. Take a look at our Yelp page and contact us today (818 248-7436), to see what we can do for your landscape.
By Daniel Williams
Client Liaison for Creative Concepts Landscape Management