GARDENERS FACTSHEET NO. 5
MULCH FOR YOUR GARDEN
Dr. John M. Gerber
Mulching garden plants is a common practice
throughout the world. It is especially important here in the
Virgin Islands where rainfall is erratic because mulch will
protect plant roots from heavy rains as well as conserve
soil moisture during periods of drought.
Mulches that cover the soil serve as protection for
the plant roots. Raindrops fall with tremendous impact and
can break up the soil crumbs which promote drainage. A
compact, poorly drained soil will then become hard and
crusted upon drying, making it unsuitable for root
development. Heavy rains may also wash down slopes,
erode away valuable topsoil and expose roots to the
drying sun. A few inches of cut guinea grass or palm
fronds will protect the soil from the harmful effects of
direct rainfall, yet allow water to reach the plant roots.
A thick organic(') mulch or a layer of plastic will also
reduce the loss of soil water by evaporation. This is
especially important in our islands where water is a scarce
and valuable resource.
An advantage of organic mulches is that they improve
the soil as they decompose and may supply some nutrients
essential for plant growth. Organic mulches also tend to
cool the soil which may be an advantage during our hot
Mulching can be an effective method of controlling
weeds in the garden. Mulching with either plastic or a
thick layer of guinea grass will reduce the amount of time
you spend on the back-breaking job of hand weeding.
Weed seeds that germinate under a mulch will soon die
from a lack of light.
TYPES OF MULCHING MATERIALS
Although any organic material can be used for
mulching, the most common is dried grass or straw.
Sawdust, wood chips (from untreated wood), manure,
compost, paper, and large leaves such as banana or palm
can also be used. Plastic mulch is also very useful in
protecting the soil, reducing water loss and controlling
Guinea grass: Guinea grass can be cut from the
roadside for use as a mulch. The grass should be piled
around the plants to a depth of no less than six inches. A
smaller layer of grass will allow light to get through and
weeds will grow. When the grass decomposes it can be
turned under to improve the soil.
Sawdust, wood chips and paper: When using one
of these woody products, nitrogen fertilizer should be
added to aid decomposition. If nitrogen is not supplied,
microorganisms(2) that decompose the woody material
will then use soil nitrogen which the garden plants require.
Either one pound of ammonium sulfate or two pounds of
10-10-10 fertilizer per 100 sq. ft. should be spread on
the mulch in addition to the fertilizer applied to the plants.
Manure and compost. Manure and compost will
help conserve soil moisture, improve soil structure and
supply some nutrients. However, they will not prevent
growth of weeds. Since weed seeds are often found in
both manure and compost, they may actually increase the
number of weeds in your garden if they are applied on the
surface. These materials should be turned into the soil,
rather than left on top, to improve soil structure and supply
Banana leaves and palm fronds. Several layers of
large leaves around plants may help conserve soil
moisture. However, unless it is applied thickly, weeds are
likely to grow through.
Plastic Mulch: Although plastic is the most
expensive mulching material, it is widely used by
gardeners. This is probably due to the lack of organic
materials as well as the effectiveness of the plastic mulch.
Plastic is the best material for conserving water and
controlling weeds. However, it does not improve the soil
as does decomposing organic materials.
Black plastic tends to raise the soil temperature more
than organic mulches. This can be avoided by using either
white or silver coated plastic. Clear plastic should be
avoided since weeds will grow under clear plastic.
Plastic mulch should be laid over moist soil. A dry
soil that is covered with plastic will remain dry, but a moist
soil will be resupplied with adequate water through the
planting holes. Approximately six inches of the sides of
the plastic should be buried
to secure it from being blown away. Stones may then be
strategically placed to prevent tearing by the wind.
Any size plastic may be used. Although the most
common size is a sheet 3 ft. wide, it is not really ideal.
When the sides of a 3 ft. sheet are covered only a narrow
strip remains to cover the soil. A four foot wide roll is a
better mulch because it would cover more soil and
reduce the time spent weeding between rows. A large
square sheet of black plastic that covers the entire garden
will eliminate weeding altogether.
After the plastic is laid, punch holes at the
appropriate locations and plant the slips or seed through
the holes. If you are planting slips, pour some water or
starter solution(3) through the hole to help the roots settle
into the soil.
(1) organic = derived from living things (grass, trees, etc.)
(2) microorganisms = primarily fungi (molds) and bacteria that
decompose organic materials
(3) starter solution = a fertilizer solution that encourages root
Products and suppliers mentioned by name in this publication are used as examples and in no way imply endorsement or recommendation of these
products or suppliers.
Issued in furtherance of Cooperative Extension work, acts of Congress of May 8 and June 30, 1914 (as amended), in cooperation with the U.S.
Department of Agriculture, D.S. Padda, Director, College of the Virgin Islands Cooperative Extension Service. The College of the Virgin Islands
Cooperative Extension Service is an Equal Opportunity/Affirmative Action organization, providing educational services in the field of agriculture, home
economics, rural development, 4-H youth development and related subjects to all persons regardless of race, color, religion, sex or national origin.