The lone voice of horticultural reason

Don’t hire a landscaper to build a boulder wall when boulder outcroppings will do.

Finished this one in the fall, will plant it this spring (June?)

I see a lot of boulder walls in landscapes where the same need – keeping a hill in place – could have been accomplished instead by installing boulder outcroppings.

Boulders used in outcroppings are BIG – a homeowner could never install them – but in all cases, these large boulders will keep a hill or otherwise higher portion of a property in place for the next 2,000 years. Boulder walls – typically made from smaller boulders and stacked, like cannon balls – can fail in periods of heavy rain. Boulders crashing into the car, side of the house, or swimming pool, are never a good thing.

It depends on the angle of the grade. If it’s the homebuilder cutting sharply into a hill to install a driveway, leaving a vertical or near-vertical wall of soil, yes, a boulder wall is in order (or, a vertical wall of concrete retaining wall block, God help you). Often I’ll see milder slope, perhaps 45 degrees, where a landscaper built two, or even three, boulder walls, in terrace fashion, to retain the soil. Why not a single swath of boulder outcroppings instead?

Instead of terracing, even a steep grade – 75 degrees – can be securely held in place via outcroppings. The huge advantage being that unlike a boulder wall, a boulder outcropping area can be planted, naturalized. Instead of dead faces of stacked boulders around the property, you see plants, with the boulders as textural accent.

Don Engebretson
The Renegade Gardener