MULCHES FOR ENHANCED, LOW-COST, LOW-MAINTENANCE
Malcolm Beck, Garden-Ville Horticultural Products
Jerry M. Parsons and Roland E. Roberts, Texas Agricultural Extension
The quality of food we eat, water we drink and air we breathe
-- in fact the well being of all plant and animal life -- is determined
by the quality of our topsoil. The earth's crucial thin layer
of soil must be protected, maintained, built and nourished. A
mulch cover of various materials on soil enables, conserves and
enhances our precious soil.
What is mulch?
Natural mulch consists of dead leaves, twigs, fallen branches
and other plant debris which accumulate on the earth's surface.
Bacteria, fungi and other living organisms use these raw organic
materials for food, a process we know as decay. In the natural
scheme of things, decay is Nature's way of returning to the earth
the raw materials borrowed by previous generations of plants.
Organic mulches not only conserve moisture, they also feed plants,
earth worms, microbes and other beneficial soil life by composting
at the moist earth surface. More species and tonnage of life occurs
below than above the soil surface. All soil life needs energy.
They cannot collect energy directly as green plants do, but the
feed on energy released from decaying mulch which is their preferred
As microbes digest organic materials they give off a sticky substance
that glues soil particles into a crumb-like structure. Carbon
dioxide-oxygen exchange necessary for healthy root growth and
proliferation of beneficial soil life is enhanced. Better control
of soil pathogens results.
Crumb-like or crumbly soil structure also allows water to soak
in better. Water that soaks in is held on the humus and clay particles
for future plant use. Water amounts higher than the field capacity
of a soil is filtered by organic matter as it flows downward to
feed aquifers that supply drinking water. Soils which have lost
crumb structure need mulch cover to re-build.
People can adapt natural mulching to cropping practices and to
production and landscape-use of ornamental plants by using available
living or dead organic matter and inorganic materials. Public
interest in mulch is aroused for two reasons: labor savings and
plant advantages. Native materials collected in your area are
the best mulch. It is neither economical nor environmentally feasible
to ship in barks, woodchips or some other fancy material from
a distant source when usually there are nearby materials being
Reasons for Mulching
Unfortunately, mulching does not perform instant miracles, but
it encourages better plant growth and development, and makes all
landscape maintenance operations easier. These benefits accrue
whether plants are growing in the coolest or hottest climates
or in the wettest or driest weather.
A mulch is any material placed on the soil surface to conserve
moisture, lower soil temperatures around plant roots, prevent
erosion and reduce weed growth. Mulches can be derived from either
organic or inorganic materials.
What Do Mulches Do?
Mulch insulates and protects soil from drying and hard-baking
effects caused by evaporation of water from soil exposed to hot
sun and winds. Mulched soils are cooler than non-mulched soils
and have less fluctuation in soil temperature. Optimum soil temperatures
and less moisture evaporation from the soil surface enables plants
to grow evenly. Plant roots find a more favorable environment
near the soil surface where air content and nutrient levels are
conducive to good plant growth.
Mulches break the force of rain and irrigation water thereby preventing
erosion, soil compaction and crusting. Mulched soils absorb water
faster. Mulches prevent splashing of mud and certain plant disease
organisms onto plants and flowers during rain or overhead irrigation.
The mulch covering excludes light which prevents germination of
many weed seeds. Fewer weeds provide less competition for available
moisture and nutrients. Using mulches to control weeds is safer
than applying herbicides or cultivating which can damage tender,
newly formed roots. Mulches also add attractive features to landscape.
Research and common sense have shown that a high organic content
favors soil microbes which de-toxify pesticides after they are
used and also furnishes energy needed by the microbes to make
high analysis fertilizers available to plants without the fertilizer
itself becoming toxic. This is another great benefit of
using organic mulches. Decaying organic mulch on soil keeps both
plants and beneficial soil life species flourishing so they can
help each other.
Management of Mulches
Apply mulches in a layer 2 to 6 inches thick. Layer thickness
depends on mulch material, e.g., coarser mulches are applied more
thickly. Thicker layers of mulch are placed around trees and shrubs
than in flower or vegetable beds. Four inches of loose fibrous
materials works well around trees and shrubs. The finer and smaller
the particle size, the thinner the layer needs to be. Thick layers
of very fine material block air to the roots of plants. In their
search for air, roots will grow up into mulch, which can be harmful
to plants if the layer of mulch is not constantly maintained.
Organic mulching materials should be added regularly to maintain
the desired layer thickness. Shredded branches from tree trimmings
and large two-inch bark is a fibrous or loose mulch. Leaves or
leaves mixed with some grass clippings and one-inch size bark
would be a medium mulch. When using medium mulch, the layer should
be about two inches thick. One-half inch and smaller materials,
such as fine-screened and double-ground barks, should only be
one inch thick layers. When piled to thickly, these tiny particles
can quickly settle together and prevent air and water from penetrating
into the soil. The finer, smaller materials should be used around
small flowers and vegetables.
When applying mulch around plants, cover the entire area of soil
containing roots. Do not pile mulch against tree trunks. It isn't
needed against trunks and may do harm. Donut mulch around plants
to be benefited allowing the plant to be in the hole of the donut
Mulches can increase availability of certain elements in the soil.
Gardeners can make a synthetic chelate with mulch by mixing one
cup of iron sulfate (copperas) to each bushel of mulch applied.
Iron particles will adhere to the surface of the mulching material
and will be released for plant use as decomposition occurs around
plants. Iron sulfate treated mulches are also effective when incorporated
into the soil.
Mulching Your Lawn
The Texas A&M Don't Bag It Program which encourages people
to mow frequently and allow grass clippings to remain on lawn
areas, and mulching lawn mowers are best for mulching your lawn
naturally. However, most lawns will benefit from additional mulching.
Naturally you wouldn't use the same mulch you put around flowers,
shrubs and trees. It is best to supply one-half inch of fine screened
compost in the fall or early winter after the grass has stopped
growing. During periods of water restrictions, cover bare areas
or dead turf with one inch of a red sand : compost lawn dressing
mix to precondition the area for replanting when water is once
again available. Remember, all grasses and grass seed must be
watered AT LEAST twice a day for 7 to 10 days after sodding or
sowing to insure stand survival and water restrictions prohibit
such water use. The use of lawn dressing during drought conditions
will insure a rapid establishment of lawn grasses when planting
can occur and will make unsightly areas more attractive.
Lawns are our biggest water consumers. For this reason lawns are
the most important places to practice water conservation by mulching.
Lawns with no crumb structure, no humus, no beneficial soil life
or root colonizing microbes require more care.
Watering with Mulch
While mulches do retain moisture in the soil, it will still be
necessary to water plants growing in mulched soils. Water should
be targeted beneath the mulch specifically at the root zone of
desirable plants. Drip irrigation is the most efficient, effective
The only fate worse than thirst for a plant is death. In fact,
death can follow severe thirst! Even if some folks are wise enough
to know when to water a thirsty plant just seconds before it crosses
death's threshold, these procrastinators are still losers. When
a plant thirsts and is severely stressed, overall vigor and production
(of flowers and fruit) are decreased. Shrubs display foliage abnormalities!
Flowers bloom with mediocrity! Trees do not grow rapidly! How
does one know when to water?
When to Water
Soil moisture level is the best criterion for watering. If soil
moisture is adequate, don't water, even if a plant is wilted.
To test for soil moisture, probe around plants with your finger.
If the soil is moist several inches deep, i.e., will form a ball
when squeezed, there is adequate moisture present.
How to Water
You may know when to water, but you may not know how. Knowing
"how" may be the most important part. First of all,
plant soils need to be thoroughly wet not saturated. These are
not swamp plants we are trying to grow. If treated as such, garden
plants and most trees will respond appropriately by dying. Deep
watering is desirable to insure development of deep, drought-tolerant
It is best to water plants thoroughly and deeply with drip irrigation.
"Drip or trickle" irrigation is a unique method which
allows precise application of water in the immediate vicinity
of plant roots. Soil moisture in the root area around the plants
is maintained at a uniformly optimum level throughout the growing
season. Small amounts of water are applied frequently to replace
that withdrawn by transpiration of water from leaves. Most water
loss by evaporation from the soil IS PREVENTED BY MULCH! Growth
and production of plants is greater with uniform watering (kept
moist - not too wet or dry) rather than being subjected to wet
and dry cycles which normally occur with other irrigation methods.
Operation of a drip system for three hours per day every other
day will insure adequate soil moisture. Distribution and evaporation
losses are minimized. Less of the total soil surface area is fully
wetted than with sprinkler systems. Normally, only 25 percent
of the soil surface is wetted with drip. This significantly reduces
the amount of water required for irrigation. This does not reduce
the plant's water requirement.
Drip irrigation also simplifies irrigation procedures and reduces
labor requirements. Drip systems can be easily activated from
one faucet. A drip irrigation system also waters otherwise forgotten
or missed plants. Once drip hose is installed around shrubs, vegetables
and flowers, it never "forgets" to water - - it specifically
waters each and every plant.
Drip systems are available at most local nurseries. Try one and
reap the many rewards which it offers. Drip systems can be used
to water during periods when drought restrictions forbid most
other types of watering. However, drip systems are not fool proof
and must be properly maintained for best results.
Proper Use of Mulches
In garden beds planted every year, organic mulches can be incorporated
into the soil each year to improve soil structure. New mulch is
applied each year. Regardless of the source of organic matter,
two factors are important to the user. One is the stage of mulch
decomposition and the second is relative salinity of the material.
Manures and sludges are usually saline and may sometimes cause
trouble unless used in moderation.
One question with organic mulches dependent upon the state of
decomposition is whether to add a nitrogen source to the mulch.
Many fresh materials may require this to avoid nitrogen tie-up.
The microbes decomposing untreated wood and bark use nitrogen.
In this example some nitrogen must be added. Slow-release nitrogen
fertilizers are much more effective. When required, nitrogen can
be added at the rate of one-half pound of actual nitrogen per
10 cubic feet of material.
Municipal Tree Trimmings - Using local mulch (from municipal
tree trimmings) around plants has certain advantages over pine
or hardwood bark. The contents of the local mulch is much closer
to the contents of rich compost. The local mulch blend actually
feeds plants being mulched but bark usually causes nutrients to
be robbed from plants being mulched.
Bark (Pine) - Ground bark is available mostly from pine
trees in sizes ranging from 2-inch chunks to a fine grind. It
provides an attractive long-lasting cover and is usually reddish
brown in color.
Grass clippings - These should be used only before grass
seed has ripened, must be spread thin (two inches or less) and
allowed to dry. If applied too thick they will build up heat and
foul odors and become slimy during decomposition.
Compost - This dark colored material is easily spread and
has slight nutrient value. It may be highly satisfactory where
available from commercial producers or homeowners.
Peat Moss - Fine texture and good color are characteristic
of peat moss, but it has a tendency to dry out and become impervious
to water. It is costly to use in large quantities. Domestic peat
moss may be so finely ground that it will blow away and is difficult
to wet if it becomes dry. Water may run off rather than be absorbed
Pine Needles - Needles are green when fresh then turn reddish
brown to gray upon drying, are long-lasting and supply nutrients
as they decompose. Pine needles make attractive mulch which is
good for acid-loving plants such as azaleas, gardenia, and hydrangeas.
Sawdust - If fresh sawdust is incorporated into the soil,
supplemental nitrogen should be added to prevent nutrient deficiencies.
Shavings - Shavings last longer than sawdust and will not
mat as badly, decompose rapidly but blow away easily during strong
winds. Wood chips mixed with shavings pull much nitrogen from
soil. Nitrogen level must be increased.
Straw - Straw is coarser, more durable than most kinds
of hay, and in most instances, is not attractive in ornamental
plantings unless chopped. Straw requires applications of nitrogen
because of its non-decomposed nature.
Wood Chips - In landscape operations wood chips offer a
useful method for disposing of waste twigs and branches. It is
good mulch, coarser than sawdust and less likely to cause nitrogen
deficiency. Wood chips are long-lasting, lie flat, and do not
blow away easily in strong winds. Cypress chips do not decompose
within our lifetime and disrupt water movement in soil into which
they have been incorporated so DO NOT TILL CYPRESS CHIPS INTO
THE SOIL!! Instead, rake or pull cypress mulch off beds before
tilling and re-apply again after planting.
Inorganic materials used for mulches do not add nutrients or humus
to soil and do not decompose except after long exposure to weathering.
Otherwise these materials are effective mulches, and several are
permanent and quite attractive.
Crushed Rock - Crushed volcanic rock or stones are available
in many colors or sizes and make a permanent cover. These materials
are especially useful around plants subject to crown rot. Spread
deeply, crushed rock can be walked on immediately after watering.
Remember that white rock radiates sunlight and can create too
much heat for most plants to survive. Black rock absorbs heat
and can cause soil temperatures to be hotter than normal. A caution:
Inorganic mulches of this type are exceedingly difficult to maintain
and keep clean under pine or other very small-leaved evergreens.
Pea Gravel - Pea gravel is an attractive permanent mulch.
It is usually applied 2 to 4 inches deep and can be reused indefinitely.
Pea gravel in various sizes is especially good for soil surface
around plants in containers.
Plastic Film - Plastic film is used to cover vegetable
beds. In ornamentals it is often used under gravel or stone mulches.
It is not practical under sharp stones unless used with 1-inch
layer of sand between soil and stones. Plastic is difficult to
dispose of when used on large areas.
Conserving moisture, slowing flood waters, reducing pesticide
use, healthier plants, smothering weeds, saving money recycling
materials considered waste -- and on and on. We still have not
yet discovered all the benefits of mulching. WE HAVE DISCOVERED
that the proper use of mulches can help us and our plants make
it through the hot, dry times ahead -- AND IN STYLE!! Mulching
is about SAVING (plant life, resources, environment, labor) FOR
NOW AND FOREVER!!!!