The RHS Chelsea Flower Show may be the world’s most distinguished gardening event, but it doesn’t have the Pothole Gardener. To hear how this planter constructs landscapes in road divots or to take part in dozens of other offbeat horticultural happenings, you’ll have to attend the inaugural Chelsea Fringe Festival, taking place around London at the same time as the flower show. The Daily Telegraph garden columnist Tim Richardson contemplated the parallel festival for two years before announcing it last May “to force myself to do it,” he says. More than 100 groups and “visionary individuals” initially responded. Many, like the “plant graffiti” artist who sprays walls with algae, are decidedly fringy, but equal numbers will plant trees, tend community gardens, and make permanent contributions to London’s neighborhoods.