Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001800
11/12/99
Inert Mulches
These materials do not have plant material as their
origin, but in many respects they may be similar to
organic materials as mulches.
Physical Effects
Using inert materials sharply limits evaporation of water
from the soil surface and overly wet conditions could
develop in heavy, poorly drained soils. Mulching with
inert materials helps maintain good structure on the soil
surface by protecting the soil from the dispersing action
of water from rain or irrigation. Cultivation, of course,
is unnecessary when inert mulches are used. The soil
temperature under inert mulches is more uniform than it
would be if no mulch were applied. When clear or
translucent plastic materials are used, the soil warms
rapidly. Such materials may raise the temperature higher
than opaque materials.
Chemical Effects
Limestone or acid-derived gravel affect soil acidity but
there are no other chemical effects.
Biological Effects
The fairly uniform moisture and temperature under the
mulch are conducive to development of various
micro-organisms in the soil. This could be favorable or
undesirable, depending on the nature of the effect of the
organism. As the temperature increases, organic matter
decomposes more rapidly, releasing nitrogen that is
available for plants. Soil granulation could be promoted,
but disease-causing organisms would also flourish. Weeds
or weed seeds are not introduced with inert mulches.
Inert Mulch Materials
Asphalt Paper
Asphalt paper can be difficult to keep in place and can
become unsightly. Tar is toxic to plants, so paper
treated with tar should not be used as a mulch.
Crushed Stone, Gravel, Pebbles
Various types of stone may be used for the effects they
create. The material may be colored to blend in with the
features of the home, patio or landscape. Stones used
near lawn areas may get into the grass where rotary mowers
could throw them and cause injury or property damage. The
stones may also be handy ammunition for vandals. Stone
mulched areas are difficult to keep free of debris, such
as leaves and stems.
Fiberglass
Fiberglass is available as building insulation or in a
woven or pressed mat. The insulation type is rather loose
when dry, but it packs down when wet. When you handle the
dry material, small pieces may break off and irritate the
skin or eyes. The mats are preferable for mulch but must
be fastened down to prevent their being pushed up by
perennial weeds. Mats may be cut and placed around plants
in the landscape or containers. They are effective in
suppressing weeds.
Polyethylene Film (Black Plastic),Polyethylene-coated
Paper Or Plastic Cloth
These black materials are popular as mulch not only in the
garden but also around the home, where they are often used
under stones, wood chips or other such materials, though
organic mulches on top of plastic may float away during
heavy rains. These materials are quite effective in
preventing weed growth. (Clear or translucent materials
applied over the soil surface will not suppress weed
growth because light penetrates and undesirable plants
will grow beneath the plastic.) Prepare the planting bed
and apply fertilizer before applying plastic mulch.
Future applications of fertilizers or herbicides will
require your pulling the plastic up so you can distribute
the chemicals evenly. Soil can be used to hold down the
edges of the plastic and prevent the wind's blowing it
away. Set plants in slits cut in the material with a
knife. If you use strips wider than 3 feet, additional
slits may be needed to permit water to enter the soil.
The plastic cloth allows good moisture penetration.
Rodents can become a problem, particularly if the plastic
is laid in the fall. Poisoned baits offer the most
effective method of control. These baits are available
from garden centers and retail nurseries.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
Extension. Reprinting cannot be used to endorse or advertise
a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
For more information about this data base or its contents please contact
heatley@msue.msu.edu . Please read our
disclaimer for important
information about using our site.