The Untapped Power of Gravel Gardens

By Kenton Seth Photos: Julie D Lehman, Horticulture & Open Space Manager at At Denver Parks & Rec

Many garden terms elicit mixed, visceral reactions. “Xeriscape” can conjure either progressive oasis or dead moonscapes. “Weed fabric” calls up passive maintenance or philosophical anathema. “Irrigation” can mean broad possibilities or an unchecked social addiction. The term “gravel garden” can do the same so it’s time to talk about it. 

Summer at 7th Ave & Detroit gravel garden, Denver. Unlike woodchips, deep gravel retains moisture without rotting the crowns of low water plants.

Beth Chatto, the heroic English gardener charged with planting a former parking lot, is without question the inventor of gravel gardening. She developed a style that not only overcame limitations but introduced a new aesthetic and way to succeed with xeric plants. It was a fresh look to see space between plants, especially plants offering less sheer petal power but more texture, shape, and fun foliage. Chatto’s garden was revolutionary: mulched with gravel, watered less (if at all) during summer dry spells, and with dead plant matter removed to keep the soil lean. Does this sound familiar?

A Colorado xeriscape garden is identical, isn’t it? - or the juicy cover of a High Country Gardens catalog. Xeric gardeners understand gravel. The City of Denver has a couple of cutting-edge gravel gardens, including one in the median at University Blvd on First Avenue, dense with pollinator forage. America’s most famous example is in Philadelphia’s Chanticleer Garden. Traditional landscapers use coarse gravels heavily over fabric and drip lines. But gravel has more potential and could be leveraged better in Colorado.

Newly planted gravel garden at 7th Ave and Detroit. Loosening the soil first makes for much better plant establishment, but it is not tilled or given compost which would encourage long-term weeds.

Weed fabric is inappropriate in a gardener’s playpen. Designed for low-care landscapes, many have seen the unfortunate collapse of this system: the soil cycle is interrupted, a dust layer becomes isolated on top, and only the worst weeds are left to colonize it. Others dislike the idea of buried plastic tangled with choking tree roots, often nearly drowned by overactive drip systems. Here is where gravel gardens can be adapted to help.

7th Avenue & Detroit Street: Plants with interesting textures, shapes, and foliage are well-suited to low water gravel gardens.

The Deep Gravel System

At 4” deep and using a 1/2” screen-size, gravel will prevent weed and flower seeds from germinating. Meanwhile, dust is able to settle to the soil, whose hidden surface is very rough, absorbing water and oxygen beautifully. Such great depth insulates the soil like any mulch, but more so, retaining moisture for a very long time. Half inch (or 3/8”, or 5/8”) sized gravel is easy to dig through. Larger sizes are hard work with a shovel (but make a nice stable surface in a street-side landscape setting like a median). Unlike woodchips, gravel will not rot the crowns of plants and can be snug around their little stems.

The soil of a new gravel landscape, especially when compacted from new construction, must first be loosened with a ripping bar on heavy equipment, or by hand with a broad-fork in small areas. It’s not tilled or given compost, which may encourage long-term weeds. Loosening the soil is worth the trouble, making for phenomenally better plant establishment. (Mixing gravel into the soil is done in wetter climates and debated in dry ones.) In older soils, deep-budded perennial weeds must be killed, removed, or smothered with cardboard or paper under the gravel.

Front yards and public landscapes with budgets, public scrutiny, and aspirations for ecological and irrigation-free plantings have the most to gain from these landscapes.

Where we want naturalism or variation, different gravel size and color, as well as boulders, can enhance unplanted surfaces. A thick gravel layer around prickly pear, cholla, and yucca, can reduce those tricky weeds that sprout up in their middles - an actual pain to remove.

The 4” depth of gravel isn’t appropriate for a garden where naturalizing or seeding is wanted; a thinner 1-2” depth will encourage seeding, and when weeds do try to sneak in, a fine size gravel can be hoed and dug easily. When there is heavy foliage cover from leafy shrubs or trees, with a forest-like feel, woodchips or plant cover may be more appropriate. Deep gravel may be unnecessary under a dense prairie or meadow planting, but has been used in midwestern meadows to reduce weeds. Note: Pea gravel will roll dangerously onto sidewalks; it can either be pinned down with larger gravel on top or sharp/crushed gravel used instead.

Especially if adapted into “gravel landscapes,” this system can supercharge unirrigated plantings and rain-trapping (or rain garden) designs. We don’t know how many more types of plants can be grown without irrigation if they have a super hefty gravel mulch. It could be foundational in xeriscapes whose owners want the desert look with space between plants, perhaps leaving some areas invisibly open to re-seeding with a thinner layer. Patches of unplanted and fabric-free gravel can serve as restful negative space, standing in for lawn that’s often used for that purpose. Front yards and public landscapes with budgets, public scrutiny, and aspirations for ecological and irrigation-free plantings have the most to gain. There is unreleased potential in humble gravel.

Kenton Seth is a garden designer and consultant with a small passive solar nursery to grow plant material for “future-proof” designs. His new how-to, no-irrigation home landscaping book comes out soon. kentonjseth.blogspot.com, @plantfortheapocalypse.