Mulch–a Gardener’s Best Friend

by Lyn Gannon, Master Gardener

Tired of pulling weeds? Wincing about rising water costs? Want to enrich the fertility of your soil? Then consider using mulch in your garden! Mulch, especially when plant-based, offers innumerable advantages to home gardeners including:


  • Reducing maintenance
  • Minimizing water usage
  • Equalizing temperature
  • Improving soil quality and fertility

Mulch--a Gardener's Best FriendWhat is mulch? It’s any material placed on the soil to cover and protect it. Many different materials can be used, ranging from straw to decorative gravel. But the hallmark of all effective mulches is 1) they allow air and water to penetrate the soil, and 2) they are long lasting and attractive. This article will focus on plant-based mulches, as they offer the most benefits to your garden.

Maybe you’re thinking: Hauling all that stuff is so much work! Is it really worth it? Yes! Mulch is one of most versatile tools available to gardeners. Specifically, mulch:

Controls Weeds

Mulch can reduce the many hours spent weeding your garden. Weeds rule the plant kingdom for 3 reasons: 1) Weed seeds germinate easily when exposed to light. 2) Garden soil is teeming with weed seeds; and 3) Weeds have adapted to survive under difficult conditions.

As a result, every time the soil is disturbed – even with the best intent – the germinating cycle begins again. Before long, your plants will be competing with weeds for water, sunlight and nutrients. And weeds are going to be the likely winners.

How to deal with those nasty weeds? Stop them from germinating in the first place! By blocking sunlight, you can stop them in their tracks, and give your plants a head start. Without a doubt, mulch is the most effective way to do this.

Later, once your bed is mulched, you’ll still have occasional weeds from airborne seeds. But the weeds will easily be removed, because their roots are less entrenched. If the mulch is damp, weeds will come out easily with the twist of a trowel or when pulled by hand.

Conserves moisture

Mulch--a Gardener's Best Friend

Mulch acts as a porous membrane which easily absorbs water, while simultaneously reducing evaporation from the soil. During daylight hours, plants are constantly using water. Absorbing it through their roots, they use it to process nutrients, and eventually evaporate it through their leaves.

Want to enjoy your garden while still practicing water conservation? Mulch it! Both your plants and environment will benefit. Most plants can survive when moisture levels in the ground fluctuate, but they thrive when water levels are more even. Unfortunately, weather conditions vary. Hot and windy conditions are particularly challenging because they increase plant evaporation.

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Bare soil loses moisture quickly. By adding mulch, you’ll have a buffer which keeps the water where you want it – in the soil. In the process, you’ll have healthy plants and minimize your water usage.

Moderates soil temperature

Like people, plants become stressed during extreme temperatures. Delicate plant tissue is easily damaged when exposed to intense heat and cold. During the summer, the sun can burn delicate roots hairs which lie close to the ground’s surface. Even trees are not immune – 90% of their roots lie in the top 3′ feet of soil. In the winter, the crown (base) of a plant can be easily damaged by frost. And, the longer temperatures are extreme, the more damage they cause.

Even during ordinary weather conditions, mulch can be a boon to your garden. The wear and tear of ordinary seasonal temperatures still affects the health of your plants. The key is to protect the crown and root, which form the core of most plants; the less they are stressed, the healthier your plants will be.

By acting as an insulating layer, mulch will minimize temperature fluctuations in the soil temperatures. Maintaining moderate soil temperatures, allows your plants to use their resources for growth rather than repair.

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Enhances water absorption/prevents erosion

Bare ground is particularly vulnerable to the whims of nature. Wind can cause loss of valuable topsoil. Rain can cause erosion and add silt to waterways downstream. Heat and drought can kill valuable soil microbes. Severe frosts can kill plant tissue. A layer of mulch can’t solve all the world’s problems, but it can lessen the damage caused by all the above.

Unprotected soil sheds water easily. A thin layer of garden clippings on the same piece of ground will soften rainfall and help the ground absorb water. Branches stuffed into cracked earth can lessen erosion. Think twice about tossing ordinary garden cuttings and twigs in the re-cycle bin. They can contribute to the overall health of your garden soil by protecting it from the elements.

Enriches soil

Plant-based mulches have an added advantage over rock based mixes, because plant-based mulches can improve the fertility of your soil, which is the key to healthy plants.

Soil is made up of soil particles, air and water. Half the volume of ideal soil is pore space – the area between the particles, where air and water can penetrate. Because roots need air and water, pore space is essential to healthy soil. No amount of fertilizer will solve the problems created by dense, compacted soil. Organic matter promotes a crumb-like granular soil with better pore structure, improving your soil’s water holding capacity, water infiltration, and aeration. Plant-based mulch will decompose and add organic matter to your soil, while feeding both the visible and invisible organisms that keep your garden healthy: earthworms and microorganisms.

Earthworms enhance your garden’s aeration, drainage and nutrition by ingesting, grinding, and digesting large quantities of soil. Their castings (excretions) are richer in nutrients than the surrounding soil. By adding mulch to your garden, you’ll develop a healthy workforce. Provide worms with what they need, and let them do the work!

Microorganisms are an essential link between the nutrients in your soil and plant growth. They insure your plant’s health and development through sophisticated and symbiotic relationships with plants roots. And, like earthworms, they thrive in organic matter. They perform crucial tasks such as decomposing plant residues into the simpler forms needed by your plants. They also synthesize plant hormones, add nitrogen to the soil, and make soil minerals accessible to your plants. Your plants need these critters! By placing organic matter (mulch) on your soil, you create a virtual feast for microorganisms, which will increase the fertility of your soil.

Overall, using mulch will begin an increasing cycle of growth and productivity in your garden. It will foster a vast number of plant partnerships, encouraging diversity in the soil and its environment. This, in turn, will create unique niches which support a growing web of life. In short, mulch improves soil fertility, the cornerstone of all healthy and thriving gardens.

Types of mulches


Straw, commonly used in the vegetable garden, is one of the most effective mulches because:

  • It traps air easily, effectively moderating soil temperatures.
  • It is extremely porous.
  • A bale can be easily broken into “flakes” which can be easily moved.
  • A bale of straw is so compressed, that it covers a surprisingly large area.
  • It is relatively inexpensive.
  • It can serve as an undercoat beneath a more attractive and costly mulch.
  • Worms love it!

There are different kinds of straw. Rice straw, for example, is usually available in the late summer and early fall after rice is harvested in the Central Valley. Because it is weed free, it can be used immediately. But it deteriorates quickly.

Wheat and oat straw are alternatives. They last longer than rice straw and they have a better consistency. But, neither can be used until the seeds are killed. Soak the bales with water until they are covered with 1-2″ of sprouted grass, or leave the bales exposed to rain for a month during the winter. But use the straw quickly at that point, or the bales will rot completely, and remember to place the bales where you want them to be before they get wet – they’re hard to move when soaked.

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Alfalfa Hay/Pellets

Though more expensive, alfalfa offers all the advantages of straw plus the added boost of more nutrition. Rich in nitrogen, alfalfa is used as animal feed. It can give your plants an added boost, too. It is seedless so can be used immediately, without the soaking treatment described above, and it has a longer life than rice straw.

Pellets are merely compressed alfalfa in small chunks. Sold in bags, they are more easily transportable if you don’t have a truck. Whether in bale or pellet form, alfalfa and the other straws are available at most feed stores.

Barks and hulls

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Barks and hulls can usually be purchased in bags. They are attractive, easy to transport, and they are useful for small areas. But a bag does not cover many square feet, and costs can quickly add up.

There are quite a few different types:

  • Cocoa bean hulls are appealing because initially they smell like chocolate. If applied too thickly, they can get gummy after a while. Consequently, they lose their porosity.
  • Barks have the advantage of being long lasting, attractive and allow water to pass easily to the soil. But they take many months, often years, to decompose. As a result, they protect soil, but they do not enrich as other mulches can.
  • Redwood “hair” works effectively, but can look artificial. Like bark, it takes a long time to decompose compared to other mulches.

Barks and hulls are available in bags at most hardware and garden centers and in bulk at landscaping materials suppliers such as Sonoma Materials in Sonoma, Wheeler Zamaroni in Santa Rosa or Grab N’ Grow near Sebastopol.

Yard Waste (including grass clippings, garden clippings and dried leaves)

There’s nothing as satisfying or cost effective as using materials that your own property (or a neighbor’s) generates. And this way, you are retaining all of the nutrients that those plants took out of your soil!

  • Fallen leaves are great! If you rake them on to your beds in the fall, they will soften the heavy rains’ effects on your soil, and they will protect your plants during freezing temperatures. Before using them, toss them in a shredder or a run a lawn mower over them, to prevent them from clumping. If they are dry even crumbling them with your hands as you spread them around is effective. While not as attractive as barks, they are porous and decompose quickly, enriching the soil.
  • Grass clippings are better consigned to the compost pile because they tend to clump unless they are spread very sparingly or mixed thoroughly with other materials.
  • Clippings from flower beds and shrubs, if chopped up, can be used to cover the back portions of beds. They are not attractive, but they can suppress weeds and they are an effective way of dealing with erosion.

Municipal garden waste/Chipped trees/Re-cycled wood

Our county has a number of sources which provide re-cycled materials, ground up and sorted according to size. These are worth their weight in gold. And they have the added advantage of blending easily with fallen leaves and other debris. Usually sold by the yard, they are relatively inexpensive, though sometimes transportation costs can equal the materials if you arrange for a large delivery.

Getting the right consistency of material is very important. Chunky is better than thready, to ensure good water absorption. Also, consider the source of the material and use it in your garden accordingly. Re-cycled lumber products are better used for pathways and ornamental areas than for vegetable gardens since they may be impregnated with unknown chemicals.

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Sonoma Compost at the Sonoma County Landfill and the various local tree companies such as Atlas Tree are potential sources of this type of mulch. There are also companies such as Affordable Landscape Materials that sell attractive chipped and screened lumber mulches.

Remember, compost and mulch are not the same. Compost is made up of fully decomposed plant materials and is an asset when added to your soil, as the microorganisms can use it immediately. Mulch has not yet decomposed, and only becomes compost over time. Mulch should be used as a top-dressing only: never mix raw mulch in with your garden soil, as it will deplete the Nitrogen level in your soil as it decomposes, and rob the soil of a key ingredient for plant growth


For the most effective results, before applying any mulch to a bed for the 1st time, cover the ground with cardboard or thick layers of newspaper to block the light. Overlap your material, leaving no bare ground exposed. Coarse textured mulches can be applied up to 4″ deep; fine-textured mulches only need to be applied up to 2″, since they pack more closely.

You’ll need to replenish your mulch periodically because it will decompose over time. But once you have an established mulch layer, you won’t need to lay newspaper or cardboard again.

Here are a few tips:

  • When using drip irrigation, lay the newspaper or cardboard under the drip tubing, making it easily accessible.
  • If you want to add plants after carefully covering your garden with newspaper and cardboard, don’t despair! Push aside the mulch, expose the paper, and cut an “X” large enough to accommodate your plant. Fold back the flaps, dig a hole, and add your plant. When done, lay the flaps back in place and re-cover your plant with mulch.
  • One caution: when mulching plants with woody stems, especially trees, leave a couple of inches of bare earth around the trunks. Too much moisture around woody stems can rot them.


In the case of plant-based mulches, you can use the seasons to your advantage by following these guidelines:

  • Many seeds require warmer soil temperatures in order to germinate. Therefore, start adding mulch to newly planted beds in the late spring after the ground has warmed up a little.
  • In established beds, you can add mulch earlier. By mulching as the winter rains taper, you can often delay watering plants for several weeks as the weather warms.
  • Early summer is prime time to maximize your use of mulch.
  • Over the summer months, your mulch will decompose and reduce in thickness, just in time to take advantage of the mid-fall rains.
  • Allow your mulch to continue to decompose as winter rains increase. Plants need good drainage during these months.

How to decide what type of mulch is best for your garden? As you visit local nurseries and gardens, take note of what types of mulch are used. Determine which look you prefer and which fits the style of your garden the best. Ask your favorite nursery which material they use in their demonstration gardens and why. Experiment with a few bags of different materials to see which effect is most pleasing. You may decide to use different materials in different places in your garden. Whichever type you decide upon, however, nothing will benefit your garden quite like mulch. No longer will you be a slave to weeds! You can have a beautiful garden while still practicing water conservation. And, you can be steward of your land, protecting the soil and increasing its fertility over time.