Majestic Mulch 101: Importance and Advantages of Mulching

The smart gardener’s time-saving, water-conserving, weed-busting magic carpet.

Talk about a landscaping product! It slashes water bills, improves the health and appearance of your plants, and saves your aching back. You don’t have to plug it in or buy a service warranty for it. There’s no assembly required. What I’m trying to sell you on is simple, down-to-earth mulch.

We can learn a lot about mulch from Mother Nature. Take a walk through any woods and notice the forest floor, layered in pine needles or leaves — it’s soft and moist; there are few weeds or competing plants; the air is cool; the trees are robust.

Serious vegetable gardeners have used and praised mulch for years. Now it’s time for the rest of us to become familiar with its benefits. So vital is mulching that one bill introduced in water-starved California includes it as one of its seven key points. (Read this carefully; someday soon you could be ticketed for failure to mulch!)

Whether you’re creating new planting beds or rearranging old ones, mulch should be an integral part of your plan. Here’s why.

Mulch: what it is, what it does

Mulch is any material spread atop the soil in planting beds (Photos 1-3). It may be organic (plant and tree materials) or inorganic (rock and stone).

Cocoa bean hulls and other finely ground organic materials make excellent mulches for annual and perennial flower beds. Weed barriers are not ordinarily used in flower beds.

Bark and other wood products provide an excellent mulch around ornamental bushes and shrubs. They provide excellent benefits with or without a weed barrier — if you use one, make sure it’s fabric.

Washed gravel, rock, and stone provide a permanent mulch in established planting beds. Always use a plastic or fabric weed barrier beneath rock beds and beware of rocks negative effects.

Whatever its size, shape, or form, mulch can:

  • Greatly reduce soil moisture loss. One-third of the water we consume around our homes is used on our landscaping — and half of that is wasted through evaporation. Mulch acts like a one-way door; it allows water into the soil but blocks its departure through evaporation. Mulch also limits soil erosion and runoff.
  • Eliminate or suppress weed growth. A 3- to 4-in. layer of mulch makes it difficult for weed seeds to work their way into the soil. And by blocking light, mulch makes it harder for seeds that do sneak into the soil to germinate and grow. If a weed does struggle through (and a few Rambo-like weeds like thistle and quack grass surely will), it’ll be easier to pull because the soil is loose and moist. This means you can get by with few or no chemicals and weed killers.
  • Protect soil and plants from temperature extremes. Mulch acts like insulation; it keeps the ground cool on hot days and warm on cold days. It helps moderate and protect roots and plants from traumatic day-night, freeze-thaw cycles.
  • Promote vigorous growth in young plants. Seedlings and newly planted trees and shrubs have a shallow root system, totally dependent on rain or manual watering for moisture. Mulch holds that moisture in the soil for their use.
  • Enrich the soil. Mulches add valuable nutrients to the soil as they decompose. Earthworms are attracted to the cool, rich soil beneath. Soil that normally bakes to a hard crust stays loose and moist.
  • Provide a protective buffer between your plants and trees and the damage your lawn mower and string trimmer dish out.
  • Improve your landscape’s appearance by adding color and texture to your planting beds. Mulch prevents mud from splashing your house and plants during rains and provides a clean “carpet” for you to walk on as you tend your garden. Mulch also helps visually fill in space while young plants grow to maturity to round out a planting bed.

There is no perfect mulch. When selecting one, weigh the pros and cons — how it will look vs. how it will perform; how long it will last vs. how hard it is to maintain.

Organic mulches

  • Shredded and chipped bark, compost, pine needles, corn husks. grass clippings, peanut shells —— anything that will let air and water through but not blow away can be used. The smaller the mulch, the closer it packs to keep out weed seeds.
  • Shredded and chipped tree and bark products are the most popular mulches. Cedar, redwood, and hardwoods, like oak or maple. last longer and are less likely to promote mold than pine and other softwood. Shredded-type mulches interweave into a single large mass, making them less likely to blow or float away. This makes them ideal for use on sloped hillsides or in areas where water splashes from roof overhangs. Expect to pay between 55¢ and $1.10 per sq. ft. of 3-in. deep wood mulch.
  • Grass clippings, leaves and leaf mold are home-grown mulches you can use. They do everything a good mulch should do —just use them with care. They break down rapidly, so don't use a weed barrier beneath them. Beware of grass clippings that contain heavy doses of lawn fertilizer or weed killer: these may harm your plants. They may also change the balance of your soil. Grass and leaves may smell as they decompose, so you may want to experiment with them on more remote planting beds.
  • Peanut, cottonseed and cocoa hulls make excellent mulches, especially in flower beds. Cocoa hulls smell sweet and chocolaty after a rain — a pro or con depending on your love of chocolate (Photo 1).
  • Straw, hay and pine needles make inexpensive, easily renewed mulches. Use hay and straw that was cut before going to seed. Pine needles tend to make the soil more acidic, which is fine for plants like azaleas and philodendrons, but not for others.
  • Compost provides protection and slowly feeds nutrients to the soil. Many people place wood chips or other mulches on top of a thinner layer of compost.

Rock and stone

Rock can add color, texture, and variety to your landscape It can range from plain gravel to volcanic rock to multi-colored stone, and costs between $1 and $2 per sq. ft. (plus delivery) when spread 3 in. deep.

Use rock with caution. It’s expensive, heavy and permanent. Stone can indeed complement the stone or brickwork of your home — but can also be hard-edged and out of character with landscaping, which is intended to soften the rigid lines of your home, driveway, and sidewalk.

When considering rock, remember:

  • Rock can overheat plants and damage tender stems and leaves It can act as a heat sink and literally bake some shrubs, especially low-growing ones like junipers. This is an important consideration with south-facing planting beds.
  • Rock shouldn't be used around groundcover-type plants that spread by dropping feeders that take root and grow.
  • Rock can crowd out or damage the stems of plants as they grow. Organic mulches easily move aside to accommodate the growing trunk of a tree or shrub; not so a layer of rock.
  • A fabric or plastic weed barrier must always be used with rock. Otherwise, weed seeds will easily wash down into the unprotected soil.
  • Rocks that find their way from the planting bed to your lawn present a danger when they’re thrown by a lawnmower.

That’s a lot of negatives, but rock does have its place. It makes a great pathway or border along a driveway It can also define a space around trees and shrubs that are well established Many of us have it ingrained in our heads to use rock — but most landscape architects try to sell their clients on organic mulches.

Do I need weed barriers beneath the mulch?

I’ve seen landscapers nearly get into fistfights over this question.

Weed barriers

Weed barriers (Photo 4) are plastics or fabrics laid over the soil before the mulch is applied, to further suppress weeds and limit water evaporation Some landscapers prefer not to use a weed barrier; many praise the new fabrics; others remain fanatics for the old plastic weed barriers.

The problem? Over the years, dust, dirt, and decaying matter build up on top of weed barriers, forming a thin planting bed for weed seeds. Hardy weeds can eventually take root and grow right through fabrics.

Another negative is that weed barriers, particularly plastics, prevent the nutrients from decomposing mulches to work their way into the soil. They also take away flexibility; if you want to add or remove plants, you need to deal with the weed barrier beneath.

Following is an attempt to wade through the myths and mysteries:


Fabrics, or geotextiles, cost from 20¢ to 30¢ per sq. ft. and come in a variety of materials and weaves (Photo 4).

They all allow moisture, air, and varying amounts of nutrients to work their way into the soil, yet help prevent weeds from taking root or sprouting. (Note, even the best fabrics can’t stop all weeds.)

Fabrics can be laid right up to the plant stems. and can be covered with either mulch or rock. Fabric clings to steep hills and rolling terrain better than plastic. too.

Make certain fabrics are covered with a 3 to 4-in. layer of mulch to help prevent seeds from reaching them. Mulch will also keep the fabrics from deteriorating by blocking the sun’s ultraviolet rays.


Plastic (around 10¢ per sq. ft.) is impenetrable to weeds — but it rejects rain, air, and nutrients with equal thoroughness.

This produces a Catch 22; the plastic needs to be perforated to let these elements through but in doing so provides a place for weeds to enter and germinate.

If you’re going to use plastic, use black rather than clear plastic: it does a better job of keeping sunlight from reaching weed seeds and will last longer if exposed to sunlight. Purchase the 6-mil thickness.

Also. bear in mind:

  • Black plastic absorbs and holds heat, which can damage a plant and its root system — especially harmful to young plants. It can also promote shallow root growth.
  • Never use plastic under loose or organic mulch; it produces a slippery walking surface.
  • If you do use plastic, cut a 1- or 2-ft. dia. hole around the plant so it can receive plenty of moisture. Cover any plastic completely: sunlight will quickly deteriorate it.

There are situations where you may want to consider using plastic. If you have a wet basement, slope the soil away from the house, then cover it with plastic and rock to direct water away from the foundation.

Black plastic is also a good choice for rock gardens or for gardens containing well-established trees and shrubs.

A simple rule of thumb for using weed barriers might be, the more permanent the planting bed, the more you should consider using them.

Never use them in annual flower gardens; maybe use them in ornamental or perennial planting beds; strongly consider using them in beds with mature trees or shrubs — in areas where you don’t want to spend any time pulling weeds.

Weed barriers come in many textures and materials. The woven fabric has a loose plastic weave on cue rim for strength and a fuzzy surface on the other to wick moisture down into the soil. The non-woven fabric has more of a felt-like texture. Black plastic (or in this case, black plastic with a white side for use under white decorative rock) is an effective weed barrier in certain situations.

A proper planting

There is no one-and-only way to prepare and mulch a planting bed, but here’s one proven method:

  1. Prepare the bed. Remove the sod, add black dirt if needed, loosen and prepare the soil. Slope beds away from the foundation at a rate of at least 1/4 in. per foot. Always start with as weed free a bed as possible. Pull up every weed you see — roots and all. Because weed seeds can lie dormant for years before springing to life. consider sprinkling a pre-emergent herbicide over the area to kill most weed seeds before they germinate.
  2. Install the edging. This could be plastic, wood, modular concrete pieces, boulders – almost anything that will contain the mulch.
  3. Place the plants (Photo 5). Plant as directed, fill around them with dirt, then soak thoroughly to make sure no air pockets are around the roots.
  4. Clean the bed one final time and rake it smooth.
  5. Install fabric or plastic if you choose (Photo 6). Overlap seams at least 6 in., so no bare spaces open up if the area settles. Overlap the material onto the edging. Fabric can directly contact plant stems and trucks.
  6. Add the mulch or rock (Photo 8). Three or four inches is considered optimum. Don't skimp — or weed seeds are more likely to slip in, as well as water is more likely to evaporate.
  7. Trim the fabric or plastic along the edge of the border (Photo 9).

Some people prefer to prepare and slope the bed, then lay down the landscape fabric, make slits, dig holes, and plant their greenery. This is a good method for a planting bed containing loads of smaller plants or perennial flowers, but it doesn’t work as well for bigger shrubs where all the digging and jostling involved can damage the fabric and leave soil on top of it.

Prepare the planting bed. Slope the sail away from the foundation. Pick all weeds and grasses and apply a pre-emergent herbicide to kill roots in very weedy areas. Position shrubs according to how much space fully grown plants will eventually require.

Install weed barrier by loosely laying fabric over plants, cutting an “X” through the fabric, then slipping it over the plants.

Overlap seams by at least 6 in. and let fabric run well beyond edging or borders. Trim the excess after you place the mulch.

Spread mulch over fabric to a depth at a or 4 in. Thin mulch to 2 in. around trunk and base of shrubs. Don’t let mulch come in contact with house siding — it could promote rot or insect damage.

Trim fabric along the inside, upper edge of borders. Check annually to make certain the weed barrier fabric remains totally covered by mulch — direct sunlight will cause fabrics to deteriorate.

Costs and time

When you buy organic mulch or rock, you’re usually paying very little for the product itself; it’s packaging and shipping that’s costing you. You’ll find local products much cheaper than those that have been trucked a-great distance.

Cypress bark is most reasonably priced in the South where it originates. Volcanic rock will be cheaper in its native Western states. Redwood chips will be cheapest on the West Coast.

You can buy mulch by either the bagful (usually 3 cu. ft.) or truckload, with substantial savings when you purchase large quantities. One cubic foot of mulch will cover 4 sq. ft. of planting bed. 3 in. thick; a cubic yard will cover 108 sq. ft. to a depth of 3 in.

Mulch Maintenance

Mulches and rock eliminate most maintenance chores, yet present a few of their own. In fall, leaves must be removed from the planting beds.

Shredded materials, because they interweave, are more resistant to being raked from the bed; wood chips or hulls tend more to tag along with the leaves. Blowers are an effective way to clean rock beds.

When you mow your lawn, direct grass clippings away from mulched beds —— especially those with an underlying weed barrier. Grass clippings rapidly decompose and form a weed planting bed on top of weed barriers: a real chore to correct with rock mulch.

In spring you can renew the depth and color of organic mulch by top-dressing your beds with 12 in. of fresh material. Occasionally during the growing season, fluff up your mulch with a pitchfork to reestablish air circulation.

Some mulches, particularly straw, sawdust, and wood shavings, can rob the soil of nitrogen as they decompose. If your plants appear yellow or stunted, you may need to add a high-nitrogen fertilizer.

Over time you’ll get a feel for how much weeding and watering your planting bed requires. When you do water mulched plants, stick the end of the hose down under the mulch and slowly, but thoroughly, soak the soil.