MULCHES FOR ENHANCED, LOW-COST, LOW-MAINTENANCE LANDSCAPES|
Malcolm Beck, Garden-Ville Horticultural Products
Jerry M. Parsons and Roland E. Roberts, Texas Cooperative 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
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 food source.
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 wasted.
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
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
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 structure.
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 watering technique.
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
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 root systems.
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
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
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 by it.
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
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
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
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!!!!