Eye on the Garden: A Weed by Any Other Name

August photo 1(Mallow leaves vaguely resemble a wheel of cheese, earning it the nickname “cheeseweed.”)

How is it fair, weed?
With one hand I can destroy
All that you’ve worked for

A “weed” is simply a plant that grows somewhere you don’t want it. Some are desirable under the right conditions. They may be edible and medicinal, or support wildlife. Yet certain plants, despite their potential benefits, just don’t play well with others in the garden. Their mission is nothing less than total domination of the space. The 20th Street Garden is wondrously diverse, and we want to keep it that way.

Because our native and drought-tolerant plants are thriving, weeds are reduced, but still present. Weeds have many tricks to ensure the survival of their species:

August Photo 2Little Mallow can be hard to spot when young.

1) Disguise. The Little Mallow (Malva parviflora) starts out with attractive, heart-shaped “seed leaves” that look nothing like the roundish leaves that eventually develop.  If you don’t recognize this plant right away it has a chance to get larger and take over.

August photo 3

2) Quantity vs. Quality. A bunch of sprouts coming up in an area you don’t remember planting is suspicious. Little Mallow produces thousands of seeds as a reproductive strategy. Seeds can remain viable for many years. Although many young plants will not survive, enough of them will.

August photo 4Bermuda Buttercup is one of the city’s most invasive weeds, according to sfwma.org

3) Indestructible Roots. Bermuda Buttercup (Oxalis pes-caprae) resembles clover but can be distinguished by its heart-shaped leaves. It’s easy to tear off the top of this invasive plant but far more difficult to remove the bulblets, which reproduce as deep as 8 to 12 inches below ground. Little Mallow also develops a very deep taproot once the plant gets big enough. You’ll wish you had some dynamite to help dig it out.

August photo 5The bright green leaves of Petty Spurge, center right, give it away.

4) Hide and Seek. Petty Spurge (Euphorbia peplus) quietly develops under and between desirable plants until it gets big enough to flower and produce seed. Seeds up to 100-years-old from this plant have been reported to germinate.

August photo 6No room for weeds here!

Prevention is the best defense against weeds – minimize vacant spots. A bare patch of earth is an invitation. Cover soil with site-appropriate plants that out-compete weeds. If the area can’t be planted, wood chips or rock mulch will help suppress unwanted plants. Pull weeds at least monthly to weaken deep-rooted plants and minimize seed production. Most importantly, remove weeds before they flower. We’ll never win the weed war, but it is possible to control populations so that our desired plants can thrive.

Ellyn Shea is a gardener and garden educator in San Francisco. Haiku and photos are her own.

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