What is hairy galinsoga?

Accurate hairy galinsoga identification pays off because this summer annual’s main trick is speed. Plants can start flowering a month or so after sprouting and drop seed a week or two later, so several generations can come and go in a single Pennsylvania summer.

Hairy galinsoga is a member of the aster family from Mexico and Central America. It’s mainly a garden and farm weed. You’ll rarely see it in a thick lawn, but it loves loose, rich, moist soil that’s been tilled or amended.

The upside is that its seeds don’t last long in the soil, generally a couple of years. If you can stop it from going to seed for a few seasons in a row, you can make real headway.

Hairy galinsoga identification: key features

• Flowers: tiny daisy-like heads, roughly a quarter inch across, with only four or five short white rays around a yellow button. Each ray ends in three little teeth. Rays are sometimes tinged pink.
• Leaves: opposite pairs, egg-shaped with a pointed tip and coarse teeth along the edges, 1 to 3 inches long.
• Hairs: stems and leaves are covered with coarse, spreading hairs, which is where the name comes from.
• Shape: upright and branching, usually 6 inches to 2 feet tall, often forming a dense carpet in garden rows.
• Roots: shallow and fibrous, so it pulls easily.

A close cousin, smallflower galinsoga, has fewer hairs and even smaller heads. For a homeowner, the difference doesn’t matter. You treat them the same.

Where it grows in Pennsylvania

Galinsoga is a common garden weed across the Northeast, including Pennsylvania. It prefers moist, fertile soil, so it thrives in vegetable gardens, raised beds, annual flower beds and market farms. It tends to be scarce in dry, unamended ground.

Heavy additions of compost or manure that build up soil phosphorus seem to favor it. It also spreads easily on muddy boots, tools and tiller tines, so it often moves from one bed to the next as you work.

In central PA, the first big flush usually shows up in late May or June once the soil warms, and new waves keep coming after every rain or round of cultivation through August. Plants keep flowering right up to the first hard frost, which is why a garden that looked clean in July can be thick with it by September.

Hairy galinsoga look-alikes

Few weeds have such tiny white daisies with only four or five toothed rays, which makes galinsoga fairly easy to pin down once it blooms. Before flowering, the opposite, toothed, hairy leaves are your best clue.

Common chickweed also has small white flowers, but it’s low and sprawling, with smooth, small leaves, and it grows mostly in cool spring and fall weather. Common ragweed has deeply divided leaves and green flowers. Pineappleweed has feathery leaves and rayless yellow-green cones.

How to get rid of hairy galinsoga

For home gardens, hands and hoes are the right tools. The trick is timing: get plants before they flower, and keep at it all season.

• Hoe shallow and often: a sharp hoe on a dry, sunny day kills seedlings fast. Work only the top inch or so. Deep digging brings buried seeds to the surface, where they sprout best.
• Pull before flowers: pulled plants with flowers on them can still ripen seed, and plants left on moist soil can re-root. Bag them or put them out of the garden.
• Mulch: straw, shredded leaves or wood mulch in beds blocks light from seeds sitting at the surface.
• Plant tight or cover crop: dense plantings and summer cover crops shade the soil and sharply reduce galinsoga seed production.
• Go easy on compost and manure: follow a soil test, since high phosphorus favors this weed.
• Herbicides: rarely needed in a home garden. Preemergence products labeled for ornamental beds can reduce seedlings, and glyphosate will kill existing plants but also kills anything else it touches.

If you use any herbicide, read and follow the label (the label is the law) and confirm it’s labeled for the site, especially vegetable gardens, where many products are not allowed. Spraying for hire in Pennsylvania requires a PA Department of Agriculture pesticide applicator certification.

Keeping it from coming back

Because the seeds are short-lived, a few seasons of never letting it flower can shrink the problem dramatically. Weed lightly every week from June through frost rather than one big cleanup in August.

Clean your tools and boots when moving between beds, and avoid bringing in soil or compost from galinsoga-infested gardens. Keep beds mulched or planted, and clear out spent crops promptly after harvest so late-season plants don’t get a chance to seed.

At the end of the season, don’t leave a late crop standing. A single fall flush that goes to seed can restock the soil for the next couple of years.

Questions we get about hairy galinsoga

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