The Effects of Colored Mulch on Cucumber Transplants
Hort 433
4-17-09
Your Name
Introduction:
Plasticulture is a common method used to grow vegetable crops. The term plasticulture
is used to describe the use of plastic mulches in agricultural production. Plastic is generally laid
on the ground or a raised bed along with a drip irrigation system to supply water to the crops.
Plastic mulches have many advantages and these advantages are why the practice of plasticulture
is becoming more and more popular. The first advantage of using plastic mulch is the regulation
of soil temperature. When soil temperature is increased this allows crops to be transplanted or
seeded sooner, thus allows the producer to get a jump start on the market. Some crops tend to
produce better under conditions when the soil temperature is increased. Other advantages of a
plasticulture system include, reduced soil compaction, reduced evaporation, a cleaner product,
and reduced weed problems (Sanders).
Disadvantages of using a plasticulture system include a high cost for removal, greater
initial cost, increased management, increased soil erosion, and increased crop/weed competition.
Even though there are disadvantages associated with the use of plastic mulches, many growers
have found that the advantages outweigh the disadvantages, and plasticulture is becoming more
popular (Sanders).
Plastic mulches have been used by gardeners, both home and commercial, in the belief
that they will raise soil temperatures. Plastic mulches can do this, but application is crucial. The
underside of the mulch must be in direct, firm contact with the soil underneath it. Black-plastic
mulch has been the top choice for mulching and still predominates in cool climates. In hot areas,
white plastic is actually used to reduce excessive soil temperatures. An alternative is clear
plastic. It provides substantially greater soil heating than black plastic. Clear plastic is much
more expensive than black plastic and also has rampant weed growth under it (Growing Taste).
Today there are more options available than just black, white, and clear mulch. Mulches
are available in red, green, blue, grey, and many other colors. The physics behind colored mulch
is this. When black plastic mulch is struck by sunlight, it absorbs most of the energy in that light
at all the wavelengths of significance, including ultra violet, visible, and infrared. The black
plastic them re-emits the energy as a long wavelength also known as thermal radiation. Clear
plastic on the other hand, obviously absorbs little solar energy, but rather passes the majority of
the energy to the soil underneath of it. However, white mulch doesn’t absorb much heat, but
does not allow much radiation of heat to pass through it either. Therefore, clear mulch will
produce the warmest temperatures, followed by black mulch, and lastly white mulch will usually
actually reduce soil temperatures (Growing Taste).
However, the answer to mulching is not simply black and white. In recent years, it has
been shown that selecting a plastic mulch of the “right” color can improve both growth and
yields of the crops. Choosing the right color is twofold; first it depends on the crop being grown,
and second it depends on the climate that the crops are being produced in.
The purpose of this experiment is to determine the effects that different colored mulches
will have on the growth of cucumber transplants. Our hypothesis for this experiment is that the
darker plastic mulches will create a better environment for cucumber growth than the lighter
mulches and the control with no plastic mulch.
Materials and Methods:
For this experiment three colored mulches were used and a control group with bare soil.
The colors used were blue, red, and grey. Two cucumbers were planted in potting media in each
large tray. The large trays were covered with the plastic mulch and tied with string. A drip
irrigation system was set up to provide the cucumber transplants with adequate water. There
were a total of eight cucumber transplants used in this experiment. Two transplants were used
for each color of mulch and also two cucumbers for the control group. Data was collected
regularly. Data collected included height of plant, number of male and female flowers, and soil
temperature. The transplants were grown in the greenhouses. After a few weeks of growth the
cucumber transplants began to vine out and grow tendrils. The cucumber plants were then
trellised.
Results:
The data produced from this experiment did not give staggering results. All eight
cucumber plants from their respective mulch color or control tray had similar vegetative and
reproductive growth. In the early vegetative stages each plant was measured on February 17th
and then again on February 27th. This was day zero of the experiment and day ten.
Figure 1: Figure 1 shows the plant height that was recorded at the beginning of the experiment.
At the start of the experiment, the control plants were taller.
Figure 2: Figure 2 represents the plant height after 10 days of the experiment. All the plants
were about equal in height, except for a plant in the grey mulch and a plant in the blue mulch had
grown taller than the rest.
Figure 3: Figure 3 represents the average plant growth after 10 days of the experiment. The
transplants grown with the grey mulch seemed to have the most growth. However, the rest of the
plants were not far behind.
Figure 4: Figure 4 represents the soil temperature, under each mulching condition. The soil
temperature was highest for the blue mulch and the control with no mulch.
Figure 5: Figure 5 shows the number of female flowers that each cucumber plant had.
Discussion:
Our original hypothesis was that the darker mulches would result in more plant growth,
because they would create a warmer soil temperature. The blue mulch, one of the darker
mulches used, did indeed create higher soil temperatures than the red and grey mulch. However,
the control plot also had a high soil temperature, which doesn’t make too much sense. This is
probably due to sources of error. In order for the mulch to function correctly, the mulch needs to
be directly touching the soil surface. It was difficult to fill the trays to the top, so that the mulch
was directly touching. Therefore the mulch may have actually been a cooling factor rather than a
heating factor, because of the air space that was between the mulch and the soil.
In this experiment the plants with grey mulch actually grew more in the vegetative stage
than all the others. Grey was one of the coolest soil temperatures. The optimum soil
temperature for cucumbers is about 70 degrees Fahrenheit, so therefore this actually makes
sense. The soil conditions and temperatures under the other two types of mulch and control
group may have actually been to warm for optimal growth. Error could have occurred with the
temperatures too, because the soil temperature was only measured once.
After the plants really took off it was hard to distinguish which plants were doing the best
because they all were growing vigorously and vining everywhere. The majority of the flowers on
all the plants were males, so we took data to see which plants had the most female flowers. The
control plot had 8, blue had 5, red had 6, and silver had 8. It should be noted that the best fruit
came from the silver tray; these plants produced some nice large cucumbers.
Our hypothesis that darker colored mulches would produce better growth than light
colored mulches can be rejected using our results, but as mentioned earlier our results do not
show statistical significance.
It was hard to evaluate the effects of colored mulch on the growth of cucumber
transplants, because our data did not show statistical significance. The main reason for this is
because once the plants started to mature they became impossible to measure. Noticeable
differences weren’t observed but this doesn’t mean that mulches (and different colors of
mulches) have little impact on the production of crops. There are many advantages that have
been proven such as increased soil temperatures (especially in early spring), less weed problems,
moisture conservation, reduction of certain insect pests, higher crop yields and more efficient use
of soil nutrients (Orzolek).
I think the main reason that significant differences weren’t observed is because the plants
were growing in a perfect environment in the greenhouse. The plants didn’t experience the cool
spring temperatures like they would have if they were growing outside. If they were outside, the
plants grown with the mulch would have definitely had a much faster start than the control plot
due to warmer soil temperatures. The different mulch colors help plant growth under different
conditions of stress; in the greenhouse plants don’t have to deal with much stress so that’s
probably why we didn’t get the best data.
For future experiments, it would be interesting to perform this same experiment in
outside field conditions. If this experiment is to be performed in the greenhouse, it would be
wise to grow crops that do not vine, so therefore they could be measured throughout the
experiment, unlike the cucumber plants.
This is an interesting experiment and should continue to be researched. If producers can
harness the use of colored mulches specific to their crops, yields can be greatly increased. With
the growing population and the decrease of farmland, yields are of utmost importance in the
agricultural industry.
References:
Sanders, Douglas C. “Using plastic mulches and drip irrigation for vegetable production” North
Carolina State University.
Orzolek, J. Murphy, and J. Ciardi. "The Effect of Colored Polyethylene Mulch on the Yield of
Squash, Tomato and Cauliflower." 2003 Web.16 Apr 2009.
<http://plasticulture.cas.psu.edu/CMulch-93.htm>.
Growing Taste: A Home Food-Gardening Resource’ “Colored Plastic Mulches for Vegetable
Gardening” http://growingtaste.com