An organic mulch
A mulch is any material placed on the soil to cover it.
Mulches suppress annual weeds by limiting the light, moisture,
and gas exchange required for weed establishment. They can
improve water penetration, regulate soil temperature, and
prevent soil erosion.
For best weed control, use a coarse-textured mulch with
a low water-holding capacity. When used alone, mulches rarely
provide 100% weed control. To improve the level of weed control,
apply preemergence herbicides at the same time as the mulch.
Supplemental hand-weeding or spot spraying may also be needed.
There can be problems associated with mulches. Some perennial
weeds such as nutsedge often have sufficient root reserves
to enable them to penetrate some mulches, such as a black
plastic. Some annual weeds will grow through mulches; others
may germinate on top of them. Applying mulches at depths
of greater than 4 inches may injure plants by keeping the
soil too wet and limiting oxygen to the plant's roots. However,
lesser depths may have less weed control benefits. Disease
incidence may increase when deep mulches are maintained.
Organic mulches can conserve moisture, prevent surface
crusting, improve water penetration, and cool the soil,
but also can harbor invertebrate pests. Mulches include
compost, very fine wood chips, grass clippings, sawdust,
leaves, clippings, chipped and shredded prunings, wood
products, and hardwood or softwood bark chips or nuggets.
Plan to replenish landscape mulches periodically because
of decomposition, movement, or settling.
Natural inorganic mulches include sand, gravel, and
pebbles. They do not provide organic matter for soil,
but do conserve moisture. If using a rock mulch, consider
placing a landscape fabric underneath to create a layer
between the mulch and the soil and prevent rock pieces
from sinking into the soil. Black plastic has been used
to improve weed control, but it restricts air and water
movement. Synthetic mulches, which are manufactured materials
that are called geotextile or landscape fabrics, have
been developed to replace black plastic in the landscape.
Geotextiles are porous and allow water and air to pass
through them, overcoming the major disadvantage of black