irower
HortiCountry
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'fp-Jt , Tim Elkner II
Lancaster County IL
Horticulture Agent jm
/
CHOOSING MULCH
COLORS FOR
VEGETABLE
PRODUCTION
Which color mulch should
you use for vegetable produc
tion on your farm? The
answer to that question is
it depends.
Color choice depends upon
the crop you are growing and
the season you are growing it.
Mulch color choice can also
depend upon whether you are
seeking insect or disease con
trol effects from the mulch.
In this article 1 will report
on some of the papers pre
sented by researchers from
around the world at the In
ternational Congress For
Plastics In Agriculture con
ducted late September in
Hershey.
Let’s start by reviewing a
little of the history of plastic
mulches and vegetable pro
duction.
Plastic mulches were first
developed back in the 19605.
The early plastic mulch
colors were black, white, or
clear. Black was used for
early crop production, espe
cially in areas with cool
spring temperatures. White
was used in areas with hot
summers since black and
clear would cause soil tem
peratures to become exces
sive.
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Another limitation in the
use of clear mulch for vegeta
ble production is weed
growth under the mulch.
However numerous benefits
from plastic mulches were
found in vegetable produc
tion. Plastic mulches in
creased yields and vegetable
quality by conserving mois
ture, keeping soil from
splashing on the crop, in
creasing or decreasing soil
temperatures (depending on
mulch color), reducing the
leaching of nutrients, and
preventing weed competition.
Then, in the mid-’SOs, the
development of colored
mulches arose. Dr. Dennis
Decoteau, chair of the horti
culture department at Penn
State (but then a researcher
at Clemson University) won
dered if light reflected by a
mulch would affect plant
growth. Building upon work
observing the effects of vari
ous colors of light on the
growth of ornamental plants,
Decoteau collaborated with a
researcher from the USDA
and developed the first col
ored mulch. This now famous
red mulch resulted in higher
early-season yields of toma
toes. By the 19905, numerous
colored mulches were devel
oped and marketed.
A recurring problem with
colored mulches has been
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variable effects on vegetable
production. One cause of this
problem is the result of the
lack of “standards” for these
colored mulches. The first
red mulch was developed
specifically for its light
reflecting properties. Unfor
tunately, other colored
mulches have generally not
been developed with this spe
cific quality in mind. Addi
tional red mulches have even
been marketed with different
light-reflecting properties
than the original. This incon
sistency is part of the prob
lem facing you, the grower,
when trying to choose a
mulch color for vegetable
production.
Another problem you face
is that even the specific light
reflecting mulches may not
show any advantage over
black mulch under ideal
growing conditions. Still an
other problem with colored
mulches is that once the crop
develops and covers the
mulch, any benefits from re
flected light are lost. So
should you abandon the idea
of colored mulches and just
use black? I would
discourage you from this
choice based on some of the
presentations I heard at Her
shey.
Let’s first discuss the use of
red mulch. Tomatoes are
generally regarded as the
crop most likely to respond to
this color mulch. Studies
from Pennsylvania showed
increased yields in tomatoes
in 2 of 3 years with red mulch
while red increased yields in
3 of 5 sites in lowa over a 2-
year study. Variable weather
conditions between seasons
and locations was cited as a
cause of the variation in re
sponse seen in both states.
Additional mulches giving
higher yields in tomatoes
were silver and IRT 100. An
other potential benefit from
red mulch that was observed
in Pennsylvania was a reduc
tion in the occurrence of early
blight, but we’ll talk more on
this later.
Peppers responded best to
nonreflective silver mulch in
two separate studies in Penn
sylvania. Green IRT and red
UV mulch also increased
yields for one year and blue
mulch was beneficial one
year but not the next. In New
Jersey, pepper yields were
also highest both for early
harvest and total harvest on
flat-reflective silver. Other
types of silver mulches also
gave higher yields in the New
Jersey study compared to
black.
A Virginia researcher re
ported that there were no dif
ferences in yield between
watermelons grown on red or
black mulches but both
mulches were better than
bare soil. Research in Penn
sylvania has shown higher
yields in cucurbits from blue
mulches, so if you would
want to try an alternate
mulch color, f would start
with blue.
Bill Lamont from Penn
State reported that all
mulches combined with tric
kle irrigation were better for
potatoes than bare soil. High
est marketable yields were
obtained with red and silver
mulch for Dark Red Norland
and similar results were seen
with NY 101 (Keuka Gold).
Researchers working with
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FERRI
Mulcher/Mower
leek in Belgium found that
the best crop (10 percent
weight increase) was pro
duced using white mulch.
They noted more even soil
temperatures than with bare
soil as well as more even
moisture under all mulches.
Another cool season crop
radicchio was grown on
white, silver, red, black, clear,
and blue mulch in New York.
Heads were smallest on blue
and bare soil and overall
yields were best on white and
silver, especially compared to
bare soil. Since both of these
cool-season crops responded
best to mulches that tend to
lower soil temperatures, I
would suggest that you try
these colors of mulch on
other cool-season vegetables.
Researchers in Georgia re
ported that all mulches, even
white on black, decreased
growth and yield of tomato
during the summer. Mulches
resulted in soil temperatures
that were harmful to root
growth under Georgia’s
summer conditions. While we
generally do not have the ex
tremely high summer tem
peratures in Pennsylvania
that they experience in the
south, I advise you to be cau
tious using dark mulch
during plant establishment in
the summer months. You
could increase soil tempera
tures too much for root
growth even here.
The use of black mulch,
however, is beneficial in the
early production of warm
season crops. Researchers in
Mexico reported that the
highest yields of muskmelon
established early in the
season were found on black
plastic. Most growers have al
(Turn to Pag* 11)
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