Mulch: earthy mix, garden fix

Times Staff Writer

Mulch is so basic to gardening that it’s become a verb. To mulch. It can even be conjugated. I mulch, he mulches, nous mulchons.

In fact, mulch is a noun derived from some kind of old German or Middle English term for largely rotting material: leaves, grass clippings, hay, ground-up wood, pebbles. Newspaper works. Mulch is anything that can be spread on top of soil to keep spring rain in and summer heat out.

Everyone with a garden should mulch, especially now, to conserve the benefits of a 100-year-rain. But beyond being good to your soil, there is its profound beauty. Mulch distinguishes a garden from a yard. Nothing focuses your eyes on a plant like an even, deep-textured background.


Ask biologists, “Why mulch?” and looks don’t come up. Rather, the talk is all about function. Mulch doesn’t just conserve water, they say. It keeps down weeds, improves soil structure, prevents dust. Use an organic mulch, and another instant plus is improved soil health. As it rots, worms appear, birds begin gleaning, a little forest-floor ecology starts.

Ask them about the downside, and they’ll warn that there can be a slight and temporary nitrogen drain, and one has to be sure to mulch with safe material. If a tree is chopped down because of disease, don’t grind it up and spread it around the base of healthy trees.

But the conclusion is always to mulch.

“You are way more likely to kill a plant by not mulching,” says Vic Claassen, a soil scientist at UC Davis.

Mulch prevents clay hardpan from forming, says Claassen. This acts as a seal: Water, instead of penetrating the soil and being taken up by plants, puddles at plants’ roots. Mulch fights this compaction, because it breaks down into chunky organic matter that aggregates with the dirt to form healthy, loose soil.

Anyone who has walked down a city street or looked at any common civic flower bed will have seen the consequence of not mulching. Shrubs and street trees arch out of dusty clay. Compaction is so bad that irrigation runs off into gutters.

When it’s dry, and yard workers and maintenance crews work the streets with leaf blowers, dirt flies up along with the potato chip packets and cigarette butts. Dried out and then slowly broken down, soil around the tree has turned to dirt and is becoming airborne, where it will be particulate matter until it comes back to Earth as dust.

All it takes to break the cycle is mulch. The best place to start is to capture what your garden already produces. Most trees are self-mulching. Pine needles, oak leaves, acacia and avocado leaves are first-class mulches. Leave them where they fall. Let them accumulate, and soil health will improve almost instantly.

Leaves fall around the tree instead of into its center for a reason: A buildup of soil around the crown would cause fungal disease, or crown rot, and slowly kill it. So let an earth line show around the base of the plant.

“It is a common reason for tree death,” says Timothy Phillips, superintendent of the Los Angeles County Arboretum & Botanic Garden.

Importing mulch is necessary when a young garden isn’t mature enough to generate what it needs. Las Pilitas nursery, whose website,, is an unofficial Southern Californian gardening bible, recommends using arborists’ clippings and shredded redwood bark around native sages.

Arborists clippings are the city’s biggest untapped resource. Most tree trimmers, even city ones, will deliver either for free or a nominal charge. However, they only deal in 10-wheel truckloads, and before one of these is dropped at your curb, it’s best to have a plan.

The city will not take kindly to your leaving a mountain on the parkway. Get it dumped into your driveway, or have it delivered on a day when you have a wheelbarrow, three pitchforks and three people to spread it. (Do not try to shovel mulch; the rim will catch. Invest in a pitchfork.) One truck should handsomely mulch the average yard.

The clippings will be “green,” meaning they are a freshly cut and ground mix of leaves, stems and sticks. This blend is perfect to allow penetration of water and air and to provide good cover. Unlike stuff from the store, it will be fragrant and relatively light to handle.

It will soon change. The leaves will decompose first and fastest. They contain the fuel, nitrogen, which canny little microorganisms will set about breaking down the minute the plant is cut. This generates heat that will cook, or compost, the pile. The higher the foliage content, the hotter it will get. In the case of trimmings from berry-rich trees, particularly hackberries, composting will help kill off the seeds.

Green mulch tends to be acidic, so it’s best not to put it directly against tender young annuals -- your tomatoes or parsley, for instance. Instead use it on beds with sages and trees, where a temporary acidification will, if anything, benefit what tends to be alkaline soil across the L.A. basin. Here, keep it clear of direct contact with a stem.

As the green mulch ages, it may briefly tie up some of the surface nitrogen. The microbes working on the mulch’s ground-up leaves don’t differentiate between nitrogen in the leaves and in the soil. Within weeks, however, the foliage is broken down, the microbes die and the nitrogen is re-released into the soil. If you’re worried about it, says Phillips, put down a light layer of chicken or steer manure.

The most important point when using ground tree trimmings from an arborist’s truck is to make sure that the cuttings are not from a tree removed because of disease, oak root fungus, pine canker or so on. Only professional composters are capable of keeping compost hot enough to kill these pathogens. You don’t want diseased plant matter in your garden.

The most logical places for mulch are our grassy front yards and parkways. If you can afford it, there’s nothing prettier in these public spaces than redwood bark. For ornamental mulch, you want longevity. Redwood bark has a good three-year lifespan, five if your dog doesn’t eat it.

Jealous of the redwood industry’s corner on the garden market, recyclers Tierra Verde Industries in Irvine got into the mulch business by using excess lumber from housing starts, dyeing it as it went through the grinder so it looks like redwood chips.

When the city of San Diego took to colorizing building waste, its recycling program supervisor Stephen Grealy found that people liked the fake thing better than the real. “It stays red,” Grealy says. Real redwood turns silver.

A newish trend around business developments is for lurid shades. Colorized mulch may one day make this most elegant fix tawdry. But so far, mulch is the only thing that in a single day’s gardening can bring a forest-floor sweetness to even the most punishing urban situation.

Landscape maintenance advisor Howard Formby of Formby Design in Silver Lake calls mulching “the single most effective fix for any landscape.” He recently brought in three trucks of arborists clippings to dress barren medians in front of a South Central school before a May fair.

“It’s good for the trees, it’s good for the air,” he says. He pauses, then adds, “It makes it look loved.”

Times staff writer Emily Green can be reached at



Just lay it on thick

Mulch is the most important element to a healthy garden. It can be any soil dressing that conserves water, prevents erosion and controls temperature. Its depth doesn’t matter in planters. Elsewhere in the garden, spread it 3 inches deep except around the plant stem, an area best kept dry.

Street trees, shrubs: Use redwood bark or trimmings from arborists.

Vegetable gardens: Try composted manure, kitchen compost, aged grass clippings, leaf mold, straw or hay, or newspaper.

Paths and parkways: In lieu of lawn, consider gravel, stone mixes or wood chips.

Potted plants: Splurge on decorative covers such as cocoa mulch, gravel and colored glass.

Conifers, oaks, avocados and specimen trees: Let the needles or leaves build up.

Native sages: Las Pilitas nursery recommends redwood bark and green mulch. Contain spillage with stone.

Desert gardens: Gravel and stone.

City mulch: Giveaway sites of green and composted mulch open daily are in San Pedro at 1400 N. Gaffey St; in Lake View Terrace at 11950 Lopez Canyon Road; in Northridge on Wilbur Avenue, north of Parthenia Street, next to the Metrolink station; and in East Los Angeles at 2649 E. Washington Blvd. For home delivery of large quantities, call Kurt Reschke at (818) 834-5128 or go to

-- Emily Green