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Tree Mulching
Improper mulching kills trees. Mulch should never be
piled into a cone around a tree trunk. This type of mulching is referred to as
a "mulch volcano". "Mulch volcanoes" waste money excess mulch and eventually
lead to diseased trees.
How should I mulch my trees?
* Start 6 inches from the tree trunk at ground level
and mulch outward to the edge of the dripline to a maximum depth of 2 inches to
4 inches.
* Keep a 2-inch to 4-inch layer around, but not touching the
base of the tree. Mulch as much of the area under a tree as possible without
having mulch touch the trunk.
* Never pile-up a cone of mulch around
the tree trunk! Mice, insects, and fungus may hide next to the trunk and feed
on parts of the tree. The cone-shaped mulch piles and thick layers of mulch
also prevent water from reaching a tree's roots. Tree roots that grow up into
the cone of mulch on top of the soil cannot be healthy.
* One layer of
woven Landscape Fabric may be used under mulch in heavy weed areas. Never use
plastic sheets under the mulch. Plastic sheets block the passage of air and
water and stunt root growth.
* Every spring or every other spring, rake
or remove any hard crust and add only enough new mulch to maintain a 2-inch to
4-inch layer. Never build up layers of mulch by adding new mulch on top of the
old mulch around a tree.
What is the best material for mulching
trees?
* Bark chunks or shredded bark that is at least 3/8 inch in
size. Pine bark will last longer than hardwood bark.
* Pine needles
*
One-year old wood chips Leaves that were shredded and composted for at least
three months
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What is the worst material for mulching trees?
* Fresh grass clippings or fresh wood chips
* Any fresh organic mulch
* Any
organic mulch that smells bad
* Peat moss or sawdust
* Pebbles, rocks, or cobble stones
* Bricks or pavement or black plastic
* Ground-up rubber tires |
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Proper Mulching
Techniques
Mulches are materials placed over the soil
surface to maintain moisture and improve soil conditions. Mulching is one of
the most beneficial things a home owner can do for the health of a tree. Mulch
can reduce water loss from the soil, minimize weed competition, and improve
soil structure. Properly applied, mulch can give landscapes a handsome,
well-groomed appearance. Mulch must be applied properly; if it is too deep or
if the wrong material is used, it can actually cause significant harm to trees
and other landscape plants.
Benefits of Proper Mulching
* Helps maintain soil moisture. Evaporation is reduced,
and the need for watering can be minimized.
* Helps control weeds. A 2-
to 4-inch layer of mulch will reduce the germination and growth of weeds.
* Mulch serves as nature's insulating blanket. Mulch keeps soils warmer
in the winter and cooler in the summer.
* Many types of mulch can
improve soil aeration, structure (aggregation of soil particles), and drainage
over time.
* Some mulches can improve soil fertility.
* A layer
of mulch can inhibit certain plant diseases.
* Mulching around trees
helps facilitate maintenance and can reduce the likelihood of damage from "weed
whackers" or the dreaded "lawn mower blight."
* Mulch can give planting
beds a uniform, well-cared-for look.
Trees
growing in a natural forest environment have their roots anchored in a rich,
well-aerated soil full of essential nutrients. The soil is blanketed by leaves
and organic materials that replenish nutrients and provide an optimal
environment for root growth and mineral uptake. Urban landscapes, however, are
typically a much harsher environment with poor soils, little organic matter,
and large fluctuations in temperature and moisture. Applying a 2- to 4-inch
layer of organic mulch can mimic a more natural environment and improve plant
health.
The root system of a tree is not a mirror image of the top. The
roots of most trees can extend out a significant distance from the tree trunk.
Although the guideline for many maintenance practices is the drip line--the
outermost extension of the canopy--the roots can grow many times that distance.
In addition, most of the fine, absorbing roots are located within inches of the
soil surface. These roots, which are essential for taking up water and
minerals, require oxygen to survive. A thin layer of mulch, applied as broadly
as practical, can improve the soil structure, oxygen levels, temperature, and
moisture availability where these roots grow.
Types of
Mulch
Mulches are available commercially in many forms.
The two major types of mulch are inorganic and organic. Inorganic mulches
include various types of stone, lava rock, pulverized rubber, geotextile
fabrics, and other materials. Inorganic mulches do not decompose and do not
need to be replenished often. On the other hand, they do not improve soil
structure, add organic materials, or provide nutrients. For these reasons, most
horticulturists and arborists prefer organic mulches.
Organic mulches
include wood chips, pine needles, hardwood and softwood bark, cocoa hulls,
leaves, compost mixes, and a variety of other products usually derived from
plants. Organic mulches decompose in the landscape at different rates depending
on the material and climate. Those that decompose faster must be replenished
more often. Because the decomposition process improves soil quality and
fertility, many arborists and other landscape professionals consider that
characteristic a positive one, despite the added maintenance.
Not Too Much!
As beneficial as mulch
is, too much can be harmful. The generally recommended mulching depth is 2 to 4
inches. Unfortunately, many landscapes are falling victim to a plague of
overmulching. A new term, "mulch volcanoes" has emerged to describe mulch that
has been piled up around the base of trees. Most organic mulches must be
replenished, but the rate of decomposition varies. Some mulches, such as
cypress mulch, remain intact for many years. Top dressing with new mulch
annually (often for the sake of refreshing the color) creates a buildup to
depths that can be unhealthy. Deep mulch can be effective in suppressing weeds
and reducing maintenance, but it often causes additional problems.
Problems Associated with Improper Mulching
* Deep mulch can lead to excess moisture in the root zone, which can
stress the plant and cause root rot.
* Piling mulch against the trunk
or stems of plants can stress stem tissues and may lead to insect and disease
problems.
* Some mulches, especially those containing cut grass, can
affect soil pH. Continued use of certain mulches over long periods can lead to
micronutrient deficiencies or toxicities.
* Mulch piled high against
the trunks of young trees may create habitats for rodents that chew the bark
and can girdle the trees.
* Thick blankets of fine mulch can become
matted and may prevent the penetration of water and air. In addition, a thick
layer of fine mulch can become like potting soil and may support weed growth.
* Anaerobic "sour" mulch may give off pungent odors, and the alcohols
and organic acids that build up may be toxic to young plants.
Proper Mulching
It is clear that
the choice of mulch and the method of application can be important to the
health of landscape plants. The following are some guidelines to use when
applying mulch.
* Inspect plants and soil in the area to be
mulched. Determine whether drainage is adequate. Determine whether there are
plants that may be affected by the choice of mulch. Most commonly available
mulches work well in most landscapes. Some plants may benefit from the use of a
slightly acidifying mulch such as pine bark.
* If mulch is already
present, check the depth. Do not add mulch if there is a sufficient layer in
place. Rake the old mulch to break up any matted layers and to refresh the
appearance. Some landscape maintenance companies spray mulch with a
water-soluble, vegetable-based dye to improve the appearance.
* If
mulch is piled against the stems or tree trunks, pull it back several inches so
that the base of the trunk and the root crown are exposed.
* Organic
mulches usually are preferred to inorganic materials due to their
soil-enhancing properties. If organic mulch is used, it should be well aerated
and, preferably, composted. Avoid sour-smelling mulch.
* Composted
wood chips can make good mulch, especially when they contain a blend of leaves,
bark, and wood. Fresh wood chips also may be used around established trees and
shrubs. Avoid using noncomposted wood chips that have been piled deeply without
exposure to oxygen.
* For well-drained sites, apply a 2- to 4-inch
layer of mulch. If there are drainage problems, a thinner layer should be used.
Avoid placing mulch against the tree trunks. Place mulch out to the tree's drip
line or beyond.
Remember: If the tree had a say in the
matter, its entire root system (which usually extends well beyond the drip
line) would be mulched.
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