Guerrilla Grafting, a How-To Guide

When cities plant trees in public spaces, they usually go for innocuous, easy, and inoffensive specimens. Nothing that needs a lot of care, drops leaves or sap, or worst of all, bears fruit that'll make a giant mess and draw raccoons and rodents.

But this is an age of urban foraging, points out Tara Hui, a conservationist with San Francisco's Guerrilla Grafters. She's been trying for years to get the city and civic groups to plant fruit trees, arguing that the harvest could feed hungry San Franciscans. Since those efforts failed to bear fruit, Guerrilla Grafters decided to take matters into their own garden-gloved hands, surreptitiously grafting fruit-bearing tree branches onto ornamental specimens in parks and other public spaces.

So far, the group's unauthorized grafts have produced only a couple of Asian pears. But Hui and the Grafters are hoping their movement spreads, which is why they gave this reporter a copy of the Guerrilla Grafting instruction manual. While we don't endorse the group's methods (the city doesn't sanction them, after all), we offer them here, purely for entertainment:

Step 1: Find the right trees.

You can't just graft any tree onto another—the species have to be compatible. Hui suggests that would-be grafters ask local nurseries, garden clubs, university agricultural departments, or other local experts to find out what fruit trees grow well locally, and what trees would support these grafts. A flowering or ornamental fruit tree is a good bet for rootstock (Guerrilla Grafters has targeted flowering pears and ornamental cherries and plums).

Hui asks grafters to act responsibly. Guerrilla Grafters will only graft to trees that a steward has promised to care for. "This is not a destructive, prank thing," says Hui. "We're trying to help people and help the trees at the same time."

Step 2: Get yourself some scions.

Basically, a scion is a branch that will produce fruit. Gardeners trade them all the time, and they probably wouldn't mind giving a few to interested fellow gardeners. "I give away branches," points out Hui, who has a cherry tree in her backyard. "I have to prune my tree anyway, why not give the branches to someone who can use them?" If inquiries to local gardening societies don't turn up anything good, you can check local nurseries, which are usually amenable to selling off branches come pruning time. The best time to get your scions and start grafting is in late winter or early spring, when both scion and rootstock are dormant.

Step 3: Pick a graft site and a partner.

The best places to graft are branches about the same size as your scion. You want the two trees to have contact at the vascular cambium, a thin layer of fast-growing cells beneath the bark. This is best done between two branches of similar size.

Grafting is best done with four hands, particularly when you're doing it without permission. You will be more efficient (and look more official) if you work with a partner, particularly if the pair of you don't look like drunken amateurs.

Step 4: Cut.

Using a sharp knife, split the receiving branch down the center, forming a "V" if possible. Shave the bark all around the end of the scion until it tapers and is approximately the same diameter as the receiving branch. If the scion has a sharp end, use your knife to blunt it.

At this point, if you are grafting in a public area, citizens may wonder what you're doing. Guerrilla Grafters often say they're taking a pruning class and practicing on local trees. "City trees always can use some pruning," the manual points out.

Step 5: Insert and wrap.

Carefully slide the scion into the receiving branch, lining up the cambium layers. If they won't match all around, set the scion off to one side so that at least one side of the cambium has good contact. Holding both firmly together (here's where four hands come in handy), wrap the graft in a spiral fashion with stretchy tape. The Grafters suggest electrical tape, since it's cheap and comes in various colors, and advise pulling it taut and covering all cuts, extending beyond the graft and up onto the scion.

Step 6: Stand back and watch.

Some grafts fail, wither, and die; others thrive. The difference between these two outcomes is often due to a combination of experience, luck, and tree care. Trees can be pruned so that the new graft basically takes over—most of the fruit trees you buy in nurseries are grafts onto some type of hardy rootstock—or they can be left alone to do as they will.

If you're really lucky, the graft will eventually start producing fruit. Hui has a cherry tree in her own backyard that produces five different types of cherries—now wouldn't a five-cherry tree look great on your town's civic plaza?

Image source: Guerrilla Grafters; header image shows pears growing from a grafted branch.