Jessie Hemmons, 25, aka Ishknits, is crouching down, sewing what looks like a neon, blue-and-green-striped sweater onto a skinny tree outside utility-gray Hartranft Elementary School in North Philly. A line of ants streaming over the bright new yarn looks about as confused as ants can. Hemmons adjusts the placement up several inches, high enough that only the tallest dogs would be able hit it. Four more scarf-like creations still need to be put up, two cross-stitched in bright pink: “PWD,” for Philadelphia Water Department, and “SOAK IT UP” — for Soak It Up, Philly!, the city program that commissioned her to knit cozies for these skinny North Philly trees. “I just started using a machine the last few months, it’s the cheesiest, wonkiest — it’s called The Ultimate Sweater Machine.” Hemmons laughs. “I do miss doing stuff by hand,” which could take nine or 10 hours per piece, “but now I’m getting asked to do projects in a short amount of time, and … I work full-time.”

When Hemmons started yarnbombing (as this knitted subgenre of street art is called) as a hobby a few years ago, she didn’t imagine she’d eventually be working for the government. She sewed her first piece onto a bike rack at 16th and Market streets with “hands shaking, absolutely terrified,” and put up many pieces under cover of darkness, including a short-lived pink hoodie reading “GO SEE THE ART” on the Rocky statue. She’s never had any problems (“I wasn’t getting any negative feedback in terms of, uh, getting arrested”), and the Anti-Graffiti Network has said it doesn’t have a problem with yarnbombing due to its inherently temporary nature, but she didn’t want to push her luck.

Hemmons says small, out-of-the-way pieces like the ones she’s installing now generally last about four months before falling or being cut down, but the life expectancy is shorter in high-profile settings: “I did a subway seat that didn’t last an entire day, and the sweater on the Rocky statue lasted 24 hours.”

This is fine, though: Hemmons isn’t sentimental about her creations, and almost never purposely checks back in on them. This, she says, has made the experience of starting to get commissions from places like Urban Outfitters, Proctor & Gamble and the Mural Arts Program extra strange: “I have to go to the opening and stand there and watch people look at my work. It’s scary! It’s intimidating! Here, I get to run away.” And she sees the limited lifespan of yarnbombs as a pro, not a con. “You know, you look at your past work and you’re horribly embarrassed by it,” she shrugs, “so it’s kind of a blessing, in a way — like, if I knew myself at age 20, I’d probably want to punch myself. … When they disappear, I’m probably a different person.”

Going from commando-style installations to doing government work in broad daylight was pure accident. An early project involved fastening bright-pink, hand-knit top-tube protectors — which prevent bikes’ paint from getting nicked when locking up — onto random bicycles. “Apparently I yarnbombed a guy from the Water Department’s bike,” she laughs. Later, the department got in touch and hired her for their Soak It Up, Philly! program, a green initiative involving porous concrete, rainwater runoff and reservoirs underneath ordinary-looking trees all around the city. “No one can see them, so they commissioned me to knit the trees to be, like, “‘It’s under here!'” she says.

Hemmons works with acrylic yarn (organics like wool and cotton fall apart quickly) in a neon palette similar to ones found in big, elaborate graffiti tags — the brighter, the better. “It’s about taking a drab environment and shocking people into looking at something,” says Hemmons, and the key is “the brightness of it, the contrast … if I was knitting in brown and gray, it would just get lost in the background.” The colors undoubtedly stand out, particularly on the overcast day — they’re almost in another dimension from the dull gray of the school and pavement and the dusty brown of the vacant lots across the street.

Similarly bright and out of place is Hemmons’ bike, which she rode up from West Philly. It has one of the pink knit tube protectors on it, the same design she attached to the Water Department guy’s bike. The other day, as she was passing by a piece she’d installed on a bike rack at Reading Terminal Market, she noticed one of her tube protectors on a bike locked to it. “Someone had parked their bike there, and it still had one of those on it from two years ago!” she says, looking genuinely happy to have proof that at least one of the many pieces she’s thrown out into the world stuck.

(emilyg@citypaper.net) (@emilygee)

Yarnbombing demo, 5:30 p.m., and talk, 7 p.m., Thu., April 5, free, Philadelphia Art Alliance, 251 S. 18th St., 215-545-4302, philartalliance.org.