Agriculture Reference
In-Depth Information
Inorganic Mulches
Inorganic mulches include plastic films and porous weed barrier fabrics, as
well as gravel and crushed stone. The latter are really only useful for small
landscape plantings.
Plastic Films
Plastic films act primarily by forming a physical barrier that prevents weeds
from growing. Dark-colored plastics also reduce the amount of light that
reaches the weed seeds; germinating seedlings; and shoots from rhizomes,
bulbs, and other underground organs. Clear plastic films are not good choices
for weed barriers. In mild and cool climates, they serve as greenhouses and
actually increase weed growth under the plastic. Even in mild climates, clear
plastic heats up the soil, sometimes enough to damage or kill fruit tree roots.
In short, avoid clear plastic film.
Black and other dark-colored plastic films can effectively eliminate most
weed problems in crop rows. They do have many drawbacks, however. First,
for all but the smallest orchard, they require large amounts of plastic made
from a nonrenewable resource (petroleum). (So far, biodegradable, plant-
based plastic films have not worked well as weed barriers.) As the plastic
deteriorates, it creates significant amounts of waste that usually cannot be
recycled. From an organic perspective, these characteristics make the bene-
fits of plastic film questionable.
Impermeable plastic films also create challenges for irrigation and fer-
tilization: You can run drip irrigation lines under the plastic, but spotting
plugged emitters becomes impossible, and the films limit you to soluble fer-
tilizers applied through the drip lines under the plastic. Plastic films also in-
terfere with the movement of oxygen into the soil and the movement of car-
bon dioxide out of the soil. While impermeable plastic films have been valu-
able in some annual and short-lived perennial crops, their value in orchards
is debatable. In warmer climates, the use of black plastic film has been prob-
lematic because of increased soil temperatures under the plastic. Reportedly,
the problem has been particularly serious with highly dwarfing rootstocks.
