University of California Division of Agriculture and Natural Resources
by Lyn Gannon, Master Gardener, Sonoma County Master Gardeners
© Sonoma County Master Gardeners
Gardener's Best Friend
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:
soil quality and fertility
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.
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.
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.
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.
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
Unfortunately, weather conditions vary. Hot and windy
conditions are particularly challenging because they increase plant
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
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
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.
water absorption/prevents erosion
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
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.
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
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.
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.
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
It is relatively inexpensive.
It can serve as an undercoat beneath a more attractive and costly mulch.
Worms love it!
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.
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.
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
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:
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.
"hair" works effectively, but can look artificial. Like bark, it takes
a long time to decompose compared to other mulches.
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.
(including grass clippings, garden clippings and dried leaves)
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!
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.
clippings are better consigned to the compost pile because they tend to
clump unless they are spread very sparingly or mixed thoroughly with
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.
garden waste/Chipped trees/Re-cycled wood
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.
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.
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.
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.
OF PLANT-BASED MULCHES
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
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
When using drip irrigation, lay the newspaper or cardboard under the
drip tubing, making it easily accessible.
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.
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:
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.
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