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The Dry Garden: Gravel, unsung hero of low-water landscapes

July 15, 2009 |  1:20 pm

GravelFross Emily Green, our columnist on drought-tolerant gardening, says it better than anyone else: Gravel is so much more than a way to cover up dirt. It can keep sun-baked soil cooler, hold weeds at bay, reduce the need for watering and look appealing. Look for the full text of the column, including advice on how to make the most of gravel in the garden, after the jump. And stay tuned: We'll be adding a photo gallery later in the week.

In other news, Green blogs on the Metropolitan Water Board's vote to resume some rebates for conservation efforts.

-- Craig Nakano

Photo credit: Native Sons

By Emily Green

When the son of friends began using his mother’s cellphone to photograph the ground at a Sunday lunch in the garden, we grown-ups laughed. “Look at Leon.” But when Leon’s mother began looking at her son’s photographs, then showed them to me, Leon had the last laugh. There, frame after frame, were abstract compositions of mesmerizing beauty. Were Leon’s downward-looking portraits to have a title, it might have been: “Dappled Sunlight on Gravel and Fallen Leaves.”

Gravel is so much more than a way to cover up dirt. As Leon noticed, its ability to catch light makes the garden floor a dancing field of shadows. Gravel also transforms the way heat, coolness and water are retained. Then, as powerfully as anything, gravel brings music to the garden. There is nothing at once so pleasant and intriguing as the sound of footfall on gravel.

For the plants grown in and around gravel, these seemingly aesthetic qualities are biological. In the right situation, gravel is an ideal habitat for dry gardening. Before praising gravel further, it must be admitted that gravel is not a pain-free choice for the conservationist. One need only visit the city of Irwindale, home of most of the gravel that went into Southern California’s road system, to see that gravel production requires the chewing up of some rocky place. But the stillness and durability of gravel make it an indispensable tool in Southern California’s transition away from lawn as a default ground cover.

The first and most obvious place to apply gravel is on trafficked areas between planting beds. Unlike grass, gravel does not require watering and  is easily weeded (though it shouldn’t need weeding if it’s not watered). Unlike wood chips, gravel doesn’t break down and get tracked into the house by the vacuum cleaner canisterful. Pea gravel and its many colored equivalents come with softened edges, making it safe underfoot for dogs.

The second place simply begging for gravel is where hedges typically run in ruffles around the footings of our homes. Builders slap in foundation hedges for insta-coziness, but, contrary to the storybook ideal of the plant-clad home, abutting the foundation is not a good place for plants or irrigation. It courts dry rot, termites and varmints. By contrast, gravel gives an elegant, clean periphery.

Certain garden beds, too, come to life when given gravel. The Mediterranean garden’s best loved standards of lavender, ceanothus and sage all do best in a rocky medium that approximates their native ranges. If you’ve never been able to grow lavender before, give it gravel mulch and go easy on the water (very easy). You’ll be weeding out feral volunteers within a year.

The most beautiful surprise in gravel gardening might be its benefit for citrus. Snails can be rehabilitated overnight from their addiction to the leaves of oranges, lemons and limes when forced to slither across at least 5 feet of rock to reach the trunk.

This brings us back to aesthetics. There might be something prettier than light bouncing off a gravel covered bed to illuminate the underside of a ripening orange, but I haven’t seen it. At a guess, neither has Leon.

Sidebar: Practicalities

Once you’re resolved to use gravel as ground cover, the questions stack up. Where to buy it? How to choose it? How much is enough?

Leaving aside glam rock, the best all-around garden choice is usually pea gravel. This term means two things. First, as the name suggests, an individual piece is roughly the size of a pea. Second, when quarry or building supply merchants use it, it is also often the name for a rugged gravel that, at $30 or so a ton, is keenly priced but sharp-edged. So if you have children or pets, look for the more paw-friendly pebble gravel.

In this pebble category, where prices run about $80 to $90 a ton, one type called Del Rio is to gravel what Levi’s are to blue jeans. It’s pretty enough for display, affordable enough for broad use. When dry, its tan and gray stones are highly reflective. This can contribute to glare, but its tones will darken over time.
Mixes are available in more muted tones — yellow to red ones for Southwestern-style gardens and more blue to green for alpine ones. These will often cost far more than Del Rio, but not always. Comparison shopping is essential.

Start with your local building supply merchants and fan out until you have quotes from at least three suppliers. As you do so, watch the units. Measurements used in showrooms can jump from pounds to tons to cubic yards to skips in a single sentence.

The way around this mire of mixed measures is to collect quotes armed with the following information:

1. The size and type of pebble you want.
2. The dimensions of your space.
3. How thickly you want the gravel to be spread.

For size of rock, 3/8- to 1/2-inch is easiest handle. As for depth, 2 inches is a good standard cover. Go deeper and you will be slipping around in it.

You may find yourself stunned by the price differences. A recent sweep of suppliers produced a range of quotes for a hypothetical order of 3/8-inch Del Rio to cover a 50-by-50 space. Excluding tax and delivery, the estimates were $1,890 from Southwest Boulder & Stone in Fallbrook, $2,635 from Sunburst Decorative Rock in Irwindale, $1,799.50 from West Los Angeles Building Materials in Inglewood and $1,557 from Bourget Bros. in Santa Monica.

Yet if you move to a more richly toned pea gravel mix, the price tripled at Bourget and skyrocketed by five times at West L.A. Building Supply, while Sunburst and Southwest Boulder and Stone prices varied only a little. Delivery fees ranged from $150 to $310 for the greater L.A. area; a hypothetical trip from the Fallbrook supplier to Van Nuys would have cost $390.

To prepare the garden for gravel, weed the area and then rake back loose top soil. You will want some loose organic matter beneath it, but not much. What is left should be smooth. Part of the beauty of using gravel in native and Mediterranean planting beds is how the seeds will fall into the rock, then root quickly without mulch or dry soil wicking the moisture away from them.

If you order in quantity, the gravel will be dumped in the street or your driveway. To move it, have scoop shovels, at least one wheelbarrow (preferably two), and some good, hard-tonged bow rakes.

Then fill the barrow, make a test dump, rake it out. This will tell you how close together the wheelbarrow dumps should be made. Covering a 50-by-50-foot space should take two able gardeners a morning. It’s hard work, but it’s the last hard or regular work you’ll do on a gravel bed or walk until cursory weeding after winter rains. The upshot will be beautiful, tough and water-savvy.

Green’s column on low-water gardening appears weekly on this blog. For past columns, click on “Dry Garden” in the category cloud. Green also blogs at www.chanceofrain.com.

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