Something peculiar is happening on the quiet block of Julian Avenue near 16th Street, and it isn’t the erotic entertainment company in the old San Francisco armory, or the food giveaway in the parking lot next door.

Armstrong calls it a "tree memorial."

A white outline of a 60-foot redwood tree is surfacing on the dirty concrete sidewalk. With wavy branches and a dense mesh of white foliage, it’s a lone vestige of nature in the midst of urban blight.

In the three hours of morning that the tree sketch transpires, pigeons take notice, pecking their way along the sidewalk towards the inviting limbs. Pedestrians either walk over it without a second thought, or stop in their tracks to wonder how it emerged to crawl across the sidewalk in front of them. Luckily for them, a middle-aged man in mustard-colored construction pants is eager to respond to inquiries.

“Wherever there’s a neighborhood without any foliage or vegetation,” Tim Armstrong tells a curious security guard. “I go and remind them that there used to be trees there.”

While not exactly a gardener, Armstrong is behind the guerilla-style installation of the redwood on Julian Avenue and a handful of others cropping up on sidewalks around the neighborhood. On clear, still mornings, he arrives at the chosen site, equipped with baseball cleats, a leaf blower, a four-gallon pump, and fifty pounds of flour.

Flour—with a sprinkling of water—is Armstrong’s art supply of choice, and the main ingredient of his arresting white sketches of trees and other sidewalk drawings. As a current featured artist at the Mission District gallery, The Lab, on 16th Street, Armstrong will create the impermanent images on the streets and sidewalks of the neighborhood through mid-October.

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For Armstrong, the images, nearly life-size and having the white hue and unrefined imprint of fossils, represent a kind of memorial to elements of the city’s past. “It is reminiscent,” he says of his redwood, “of what the neighborhood looked like years ago before they chopped all the trees down.”

“Tree memorials I’ll do wherever there’s wood telephone poles and wide sidewalks and not a lot of trees around.”

This flour drawing, as his calls it, begins at the base of a wooden telephone pole bearing the familiar holes, staples, and “Missing Kitten” flyer of an urban makeshift bulletin board. Instead of going up, the trunk of Armstrong’s tree crawls horizontally along the sidewalk to appear as if the pole’s shadow, or the footprint of a tree that fell from the pole’s position.

“It’s the former life of the telephone pole as a tree,” Armstrong muses.

All of Armstrong’s flour drawings interact with their surroundings in a similar fashion. A dozen yards up the sidewalk from the tree, a pair of pigeons eats away at a “welcome mat” Armstrong created three days earlier. The rectangular patch of fading white curlicues and encircled letters spelling “WELCOME” abuts a chain link fence enclosing an empty lot.

The North Beach resident says he got the idea for that piece when he walked around the Mission District and came upon the vacant lot dominated by weeds growing through the fence and sidewalk. The welcome mat on the sidewalk, he says, will “give people pause.”

Pigeons eat away at Armstrong's three-day old "welcome mat."

A pigeon pecks away at Armstrong's three-day old drawing.

“Nature’s welcome,” he suggests, “or you’re welcome to stay here and contemplate the meaning of a vacant lot.”

Three days old and being literally devoured by the urban ecosystem, the washed-out image brings a smile to Armstrong’s face. “When it fades like this it just looks perfect, like it belongs on the sidewalk.”

Photographs of his flour drawings in various stages of decay are for sale for $100 and exhibited at The Lab. It’s not an art that provides a living.

He buys the material himself, and holds a day job as a hotel handyman. However, as his current residency at The Lab suggests, his distinctive technique has begun to draw attention from local curators and art schools.

A Southern California native with a shy smile and soft falsetto voice that belie his 47 years, Armstrong has spent plenty of time observing the ground below his feet. When he was a teenager, he worked with his dad as a parking lot sweeper for $50 a lot. “My first jobs were blowing leaves out for him to sweep up early in the morning,” he says. He entertained himself collecting tumbleweeds. “I would put little mirrors in them, and let them blow through town.”

It was not until years later that Armstrong began to pursue his art and eventually invent his signature flour technique.

Tim Armstrong

Shortly after his grandmother died in 1989, Armstrong had a dream in which he was blinded by a ball of light. He interpreted the vision to be a symbol of his creative energy—latent and enigmatic, but waiting to be released.

“I identified with not being here,” he said, adding that his mother had died a decade earlier. He began to channel his existential questions into artistic expression. He read about Buddhism, Tibetan sand paintings, “and how life is more beautiful because it’s transitory.”

Still unable to shake off his depression, Armstrong moved to San Francisco in 1994 to study drawing at the San Francisco Art Institute, hoping it would offer a form of therapy. Though he never graduated, he experimented with techniques of creating ephemeral art out of flour—organic images that blend into their surroundings, and within a month’s time, fade away.

Depending on their size, the drawings take three or four hours. They can be interpreted as graffiti and therefore illegal, so Armstrong works with the caution of a criminal—fast and constantly on the lookout for those who may not appreciate his artistic taste.

Armstrong even sports a disguise for good measure: a stamp on his shirt, truck, and equipment eerily resembles that seen on cleanup crews of the city’s Department of Public Works. “It’s DWP–Dead White Plants,” he explains.

He begins by dragging a circular plant border filled with flour down the sidewalk to create a thick column for the trunk.  Using a squeegee, he goes back and buffers the edges for bark. He scoops more flour into a deflated rubber ball and pours from it to draw sinuous limbs. Finally, Armstrong packs flour into a bag with holes to shake over the limbs for a sense of foliage.

Once the tree’s form is on the ground, he straps a water pump—the kind ordinarily used by farmers for fumigation—onto his back and, like the tin man, elevates and lowers his arm to pump a squeaky sprinkle of water over the entire drawing.

It isn’t until the final step that the illustration magically emerges. Armstrong uses a leaf blower to eliminate a layer of flour from the tree. What remains on the ground is an outline of the trunk and branches, filled with concrete and white splotches in the middle, like an imperfect stamp of a life-size tree.

As morning turns to afternoon and Armstrong has photographed the tree and put his equipment away, he makes a plan to monitor and document its decay. “Today I’ll go out for a burrito,” he says, “and come back and see if the birds are eating it.”