On one of San Francisco’s steep hillsides, an established garden presented an interesting planting challenge: a pronounced slope, shallow soil and beautiful shelves of exposed bedrock stepping naturally through the site.

The rock was one of the things that gave the garden its character. It wasn’t something I wanted to hide or design over. The challenge was to introduce new planting while keeping that sense that the garden belonged to the hillside.

The plan — and the ground

A planting plan gives you structure: the relationships between plants, repetition, rhythm and how the planting will move through a space.

But on a site like this, it can only take you so far.

Once we began setting out the plants, the hillside started making some of the decisions for us. A plant positioned perfectly on the drawing might land where there were only a few inches of soil over rock. Move it slightly, and suddenly there was a pocket deep enough to plant.

Groups shifted. Spacing changed. Some plants travelled rather further from their carefully considered position on the plan than expected.

And that was fine.

Working with what was already there

There was already a wonderfully established quality to this garden, with mature trees, existing groundcover and planting weaving around the exposed rock.

Rather than clear everything and begin again, we kept what was working and introduced the new plants amongst it.

The shelves and steps of bedrock began to influence the planting itself — creating natural changes in level, pockets for plants and pauses between groups. What might have been considered a constraint became one of the strongest features of the garden.

It’s also a reminder of why I like to be on site when a planting plan is installed.

The drawing provides the intention.

But sometimes, the ground gets the final vote.