Proper Mulching Technique

I have always thought "mulch is mulch". However, as Lakeland Natural Resource Director Nick Bridgeman pointed out, property mulch technique is very important.

The Lakeland Natural Resources Department provides a plethora of information on trees and landscape plant selection and care at www.Lakelandtn.gov (click on the Natural Resources tab). I learn a lot about trees and plants by occasionally reviewing this information!

The information below is courtesy of Terran Arwood, President of Woodland Tree Service.

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