Weeds you may want in your Sonoma County garden

Summer-blooming weeds surround us. They come in many forms. Some, like bindweed, star thistle, mallow, puncture vine or Bermuda grass can be the bane of our gardening and farming lives; their aggressive tendencies, resistance to removal and persistence cause much frustration and sometimes despair.

Some 97% of our native grasslands are gone, replaced by weeds, both grasses and forbs. A few weeds provide benefits to us, farmers and wildlife. Some plants considered weeds are really native wildflowers, and unrecognized, are often weed-eaten and mowed from our properties.

It is both interesting and important to get to know some of the commonly occurring weeds and native wildflowers around our gardens, roadsides and farm fields.

Birdsfoot trefoil (Lotus corniculatus) is a nonnative, grassland, perennial legume from North Africa and temperate Eurasia. Highly adapted, it grows throughout much of North America and Canada as a weed, but a number of cultivated varieties are grown as a forage or hay crop in the northeast and southeast.

It does not cause bloating in foraging animals as do other legumes like alfalfa and white clover. In our area it grows in a range of inhospitable conditions from cracks in asphalt roadways and compacted soil on farm roads to ponds, vineyard floors, roadside ditches and field margins.

While some cultivated varieties of Birdsfoot trefoil are more upright, the weedy varieties are generally very low growing.

In no-till vineyards or orchards with poor draining soil, it can form a neat, very low, green, non-irrigated ground cover throughout the field if other weeds are kept mowed low.

As the plant is nitrogen fixing, it benefits soil fertility. The profuse and cheerful clusters of pea-like bright yellow flowers are a favorite nectar source for butterflies and are also visited by bumblebees.

When in full bloom, entire vineyard floors can be bright yellow with its flowers. Deer and Canadian geese are avid consumers of the foliage. Seed can be purchased locally.

Spanish clover or American birdsfoot trefoil (Lotus purshianus) is a native legume, annual lotus somewhat resembling the birdsfoot trefoil. It is slightly taller, to about 10 inches with a mounding growth habit, has lighter green, hairy leaves and single pale pink flowers.

It grows throughout much of the United States from the West Coast to the Midwest, and north into Canada. It is found in chaparral areas, oak woodland and around our farm fields, ponds, and fence lines.

As a more inconspicuous and unrecognized plant, it is often mowed. Its leaves are a larval food for the Afranius Dusky Wing butterfly and Acmon Blue butterfly.

Beginning in late June and continuing through at October, the yellow or white flowers of native tarweeds hold sway in fields, roadsides and hillsides. Tarweeds have a distinctly sweet/sour, fragrant, sticky foliage that, when walked through, can make shoes, livestock’s lower legs and dog’s feet (especially poodles) sticky. Many people find the smell pleasant or at least nostalgic of hiking trips. There are three distinct species.

The tall (3 to 4 feet), sparse yellow daisy flowers of Madia elegans are often seen along roadsides and around field margins. Where mowed, they are smaller. Some of the flowers have decorative red centers.

Madia do well in gardens, but can seed profusely and are probably best in more wild settings among native plants. Close to the coast, plants are prone to rust.

Easy and long blooming are the Hemizonias, or hayfield tarweeds. They are much smaller, densely growing plants, to about 1½ feet, with profuse amounts of small, showy daisy flowers of yellow or white.

The fields around Sonoma State University in Rohnert Park used to be yellow with the Hemizonia congesta ssp. lutescens. Another variety has white blooms: Hemizonia congesta luzulifoli.

The plants grow in a variety of soil types; even heavy soils and serpentine conditions.

As plants begin growth relatively late in the spring, if weeds are mowed in the spring, this can allow the tarweeds to flourish without competition.

On one dam face completely covered by the very aggressive, nonnative perennial Harding grass (Phalaris aquatica), hemizonia tarweeds flourished every year after the Harding grass was mowed low in the spring.

Both hemizonias do well in the garden - in pots or in the ground, and reseeding is nil in many cases. Avoid fertilizer, but a small amount of compost will generate stronger plants that bloom longer.

Tarweed flowers open very early in the morning, and close by about noon. They are favorites of small native bees. Pollen is white and easy to see on the bees’ back legs.

The yellow variety is available at Annie’s Annuals and Perennials Nursery ( All the tarweeds are available by seed from Larner’s Seeds in Bolinas (

In late summer, vinegar weed (Trichostema lanceolatum) blooms. It is a small, upright plant that grows to about a foot tall, and has vinegar-scented, sticky foliage and very attractive violet flowers that bees love. It grows in poor conditions on rocky, nutrient-poor soil. According to accounts of early beekeepers, there used to be great swaths of it in the valleys - to the bees’ delight.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at:,, Twitter @katebfrey, Instagram @americangardenschool

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