Many types of material, organic and inorganic, may be used as mulch. Organic
mulches may break down in one season or less or persist for more than one
season. Commonly used landscape mulches include wood chips, shredded bark
and wood of various types, bark nuggets, and shells of cocoa, buckwheat
and cottonseed.
Inorganic mulches commonly used are pea gravel, stone, marble, volcanic
rock, and crushed bricks.
There is not one perfect mulch. But understanding the attributes of different
materials can help you choose the best mulch for a particular location.
There are many mulches available for use in the landscape. Some of the more
commonly used mulches are listed here.
ORGANIC MULCHES:
Processed Bark - This is an economical mulch which makes it one of the
more widely used mulch materials for the landscape. Processed bark can be
either from hardwood or pines. Some materials are a combination of shredded
hardwoods and pines, which combine to make a more consistent, longer lasting
mulch than plain hardwood.
Cedar Bark - This material can be purchased in bags or in bulk by
the yard. It is usually a product of Canada and is generally a stringy mulch
that tends to last longer than hardwood. It is
believed to repel insects.
Twice Ground Cedar Bark - This is the same as cedar bark mulch except
it has been shredded a second time, creating a finer mulch than most shredded
cedar bark.
Cypress Mulch - This is a product of Florida, which is the main reason
for its relative high price. It is a very consistent mulch from load to
load and last longer than hardwood bark; it is very popular for use around
roses. Cypress mulch is typically purchased in bags.
Redwood Mulch - (Eco-Safe Mulch) This type of mulch is the most popular
selling mulches right now because of its color and because it is made from
recycled wood. Once chipped and shredded, the wood is dyed red with an environmentally
safe coloring that allows it to maintain its original color longer than
most natural mulches. NOTE: While some companies market this product as
"Redwood Mulch", it is not a product of the tree that is native
on the West Coast.
Goldentone Mulch - This is made from recycled wood like the Redwood
Mulch but this product is dyed yellow. (The recycled wood products are also
available in black and natural.)
Wood Chips - Wood chips are derived from many different hardwood
and softwood species. They are often found on playgrounds and are used for
paths, as they don't tend to become compacted as a result of foot traffic.
They are a very economical organic mulch.
Compared with bark mulches, wood chips tend to lose more their decorative
appearance over time, weathering to a gray or silvery gray color. Because
of this, people often renew wood chip mulches each year by adding an additional
3 - 4" of ships. This overmulching not only wastes mulch but can suffocate
the roots of shallow-rooted species and cause cankers to develop around
the bases of susceptible trees and shrubs. A better practice is to renew
mulches every 2 - 3 years and churn up the existing mulch before adding
a light renewal layer. Wood chips last longer than any of the bark mulches
and but their color fades in a similar manner. They generally do not stay
in place as well as barks and have a tendency to blow or float away.
Nuggets - Nuggets or bark chips are available in sizes from ¼"
to 3" in diameter. They last many years without breaking down, but
they are not useful in wet areas or on steep slopes because they float and
easily wash away. Nugget are made from driftwood or pine bark.
Cocoa Shell Mulch - This material has a strong chocolate aroma and
imparts a delicate, richly textured appearance. As such, they are especially
useful around highly visible shrub borders, flower beds, and rose gardens.
This processed mulch is more expensive than other mulches. It may also blow
around in strong winds and wash out after heavy rains. Cocoa shell mulch
also has a high potassium content which may injure some plants. Young maples,
lilacs, rhododendrons, and azaleas have been found to be susceptible to
damage.
INORGANIC MULCHES:
(Gravel, stone, crushed brick, white marble, volcanic rock)
Inorganic mulches offer some advantages over the organic materials described
thus far. They are not blown about by wind, they do not harbor weed seeds
or diseases, and they do not rob the soil of nitrogen like some organic
types do when they break down.
Inorganic mulches are used in shrub beds, driveways, walkways, and in steps.
Depending on the material used, they can be fine textured or coarse. Crushed
stone and gravel are appropriate mulches for rock gardens. Some inorganic
mulches can be colored to blend in with features of the home patio, or landscape.
Inorganic mulch particles can work free of beds and be thrown by rotary
mowers, potentially causing injury. Unless underlaid with a fabric, they
migrate down in soils over time. White stone can increase reflected heat
and may cause additional heat stress to adjacent plant materials. Limestone
chips raise the pH of the soil and thus should not be used around acid-loving
plants.
The type of mulch to use in the landscape often depends on aesthetics, personal
preference, and cost. Another consideration is the site. In areas prone
to flooding, mulches prone to floating (e.g. nuggets and cocoa shells) wouldn't
be a good choice. Of course, aesthetics may weigh heavier in your final
decision. Although cocoa shells float, you may be willing to reapply them
because you like their dark, rich color and chocolaty smell.
When evaluating the site to be mulched, also look at the slope of the landscape.
On steep slopes, shredded mulch is best and hardwood holds better than softwood.
However, hardwood mulch tends to break down faster than softwood (i.e. pine
bark) and may need to be reapplied sooner.
If mulches are needed for pathways, select shredded bark for easiest walking.
The irregularity of shredded bark makes it easier to walk on than some of
the chunkier mulches.
Regardless of the type of mulch selected, it should be applied at a uniform
depth of 3" around and under the plants. Low or bare spots are prone
to weed problems. Avoid placing the mulch against the trunk of woody plants
because this could encourage insect and mouse activity as well as decay
organisms.
Geotextiles or landscape fabrics are sometimes used beneath mulches, especially
inorganic mulches. These woven and nonwoven fabrics
of polypropylene or polyester are an improvement over traditional black
plastic. They not only block weed growth and reduce surface evaporation,
but also allow water, fertilizer and oxygen to easily penetrate through
to the soil.
Black plastic is not a wise choice for beneath mulches in permanent planting.
Black plastic does not let air and water to reach the roots of trees and
shrubs. As a result, many plants have died due to the use of black plastic.
Although there is no "super mulch", knowledge of the characteristics
and uses of different mulches allows a homeowner to select a mulch that
will benefit the entire landscape.
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