1. Kevin Bautista
Molly Olson
Dmitriy Peresada
Season Extension:
An Experiment on the Effectiveness of Various Types of Materials in Lettuce Growth
Background
Sustainable agriculture has been brought to the forefront of the environmental
movement because of agriculture’s major role in the health of the natural environment.
Sustainable agriculture, as defined by the National Institute of Food and Agriculture, a
subdivision of the United States Department of Agriculture (USDA), is an “integrated system
of plant and animal production practices... that enhances the quality of life for farmers and
society.”
Sustainable agriculture has the potential to greatly reduce problems such as global
climate change and environmental pollution. Locally grown produce reduces or eliminates
food miles (the distance food must travel between production and consumption), which
significantly decreases harmful CO₂ emissions. 250,000 tons of global warming gases per
year are attributed to importing food products—the equivalent amount of pollution produced
by more than 40,000 vehicles on the road or nearly two power plants(National Resource
Defence Council).
Currently, due to the current economic practices of the food industry, a lot of produce
and meat are transported thousands of miles when they could be obtained locally. For
example, “​
Seventy­five percent of the apples sold in New York City come from the West
Coast or overseas,... even though the state produces far more apples than city residents
consume” (McWilliams). Not only does local produce reduce the carbon footprint, but it also
holds more nutritional value. Locally grown produce does not have to be shipped out before it
ripens and also does not have to be treated with artificial ripening agents. Additionally, locally
grown produce does not have to travel hundreds or thousands of miles to various parts of the
food system before it reaches the consumer.​
In 2006, the State of Illinois tied with Texas as
the third largest exporter of agricultural products, specifically soybean and feed grain (Brooks
2007). High­volume production harms fragile ecosystems and drinking water supplies around
Illinois due to the use of artificial fertilizers and pesticides (Brooks 2007). Agriculture industries
around the world use about 3 million tons of pesticides, which are formulated from 1,600
different chemicals (Horrigan et. al 2002). Pesticides and other chemicals used to allow long
distance transportation of produce also find their way into our diet. A study conducted in
France investigated the abundance of pesticide in more than 300 French wines. The results
showed that 90% of the tested wines contained traces of common chemicals used to treat
vines. “​
Some wines contained up to nine separate molecules, with 'anti­rot' fungicides the
most commonly found” (Anson 2013). These examples of pesticide­related food
contamination and damage to ecosystems as well as the high food miles contributing to the
CO​
₂ ​
emissions are unsustainable to our food system and way of life. Because of the high
density of people in an urban setting, it is especially important to grow food as close to the
area as possible because of the health benefits of fewer pesticides used and fewer CO​
2

2. emissions from transportation. Sustainable agriculture, especially in urban settings, can
reduce these problems, but there are many obstacles to overcome.
One roadblock to sustainable agriculture may include a temperate or colder climate
and urban environments, all of which make it more difficult to grow produce. New innovations
however, make it possible to grow vegetables for longer periods of time in temperate climates.
One type of “low­tech” technology is season extension methods. Season extension is a
method of growing season extension where crops are protected by a type of greenhouse
material that shields them from the elements and keeps the soil warmer. Using season
extenders, we want to predict how Chicago’s somewhat unusual seasonal climate changes
will influence the effectiveness of our season extension methods.
One study that demonstrated what we wish to do was conducted in India. The project
used strawberry plants and a low tunnel season extender and examined the effects low
tunnels have on crucial aspects of the environment that influence plant growth such as air &
soil temperature and humidity, as well as the ripening time of the strawberries themselves. By
subjecting strawberries to two experimental conditions throughout the year (open fields vs.
low tunnels), researchers were able to determine that low tunnels had a powerful impact on
the growth rate and ripening time of strawberries by making a more favorable growing
environment. Results showed increased air & soil temperature inside the low tunnels
throughout all seasons, increased humidity inside the low tunnels, less time between planting
& ripening, and extended fruit availability. This technology will be beneficial in many ways. By
applying this type of technique on a large scale, the local economy will flourish by keeping the
farms open longer and lessen the cost of transportation. Thus, this allows more of the profits
to go to the local farmers. It will also allow more produce to be sold in what would be
considered the off­season. Finally, this technology will lessen the amount of food miles
accumulated year­round, which reduces the amount of CO₂ emissions​
​
(​
Singh al. 2004​
).
We are utilizing the Rosemarie Rochetta Wisses Rooftop Garden on the top of the
Quinlan Life Sciences Building. Taking part of a rooftop, of which there are many in the city,
and transforming it into an edible garden is the first step towards sustainable urban
agriculture. There are eleven total raised beds on the rooftop, which had already been
constructed and used prior to this project. For our project, we used the six 4ft. by 8ft. beds to
grow Romaine Lettuce organically which will supply student­run business Felice’s with the
lettuce for salads. By growing the lettuce in the same place that it will be consumed, it
significantly decreases harmful emissions. Ideally this system would be able to supply them
year round, but because of the climate the growing season is limited. This is where the
season extension will be beneficial; by extending the season we are able to continue to grow
plants outside for a longer period of time. By growing produce on campus, we will reduce the
amount of food miles traveled, which reduces the amount of CO₂ emitted into the atmosphere.
The utilization of a rooftop takes advantage of as much available space in an urban area as
possible. Also, by testing the efficacy of different materials, we can provide the future STEP
classes with a strong foundation of season extension knowledge.
Project Overview
Our project is solving the problem of CO​
2 ​
emissions due to food miles and the pesticide use

3. of industrial agriculture that can pollute our water and enter our diets. These season extension
structures allow food to be grown for a longer period of time in a temperate climate. This
means the food can be grown where it is consumed for a longer season than food could be
grown without the structures.
There were three goals to our project on season extension.
1. The first goal was to build six experimental season extension frames, that are:
adjustable and reusable, efficient in extending the growing season, sturdy enough to
withstand windy conditions on the rooftop, and relatively inexpensive.
a. The frame of the structure was modeled after a low tunnel structure,
constructed with PVC pipes and brackets to secure it onto the sides of the
raised beds. This structure is commonly used in agriculture. We obtained
instructions for its raised bed adaptation, which can be adjusted to control air
and sunlight access . Furthermore, we intended on using three types of
greenhouse film materials to construct our season extension structures: 6 mm
greenhouse film, 3 mm Clear Overwintering Film, and Solar Max Reinforced
Poly Film (Greenhouse Megastore).
2. Second, we were going to design and execute a procedure which will determine the
effectiveness of the three different greenhouse films we employed. This would allow us
to rank the structures by effectiveness and cost­effectiveness.
a. To aid in this task, we were going to plant Kale seeds in all six season
extension beds. To facilitate the growing process and to make sure that we
have plants growing outside we were to start seeds indoors for three of the low
tunnels, one with each greenhouse material. We were going transplant them
into the beds when while planting the seeds in the three other beds. As a
control, we were to measure how tall the plants are before transplanting them
to make sure we have the same scale of height and growth rate across all of
the six beds. Our measurement of effectiveness would be a regular
temperature reading of the soil for each season extension material, followed by
the regular height measurements of the kale during the growing phase, and
finally the weight of the final harvest for each structure.
3. A secondary goal was to build similar low tunnel structures in the Winthrop Lot, if our
structures at the rooftop garden proved to be effective and if we met our primary goals
in a timely fashion.
a. This would increase the productivity of the Winthrop Lot during spring and fall,
furthering our mission of improving sustainability by reducing food miles and
pesticide use brought on by commercial agriculture.
Materials and Methods
1. Constructing low tunnels at the rooftop garden.
The instructions and materials list was adapted from the Samuel Roberts Noble
Foundation website (Permanent Raised...). While the original plans are designed for a
raised bed much greater in length than the ones found in our rooftop garden, we
downsized them(to ~4ft by ~8ft) using the original techniques and materials. The Solar

4. Max Reinforced Poly Film originally intended as the third greenhouse material, but
because of its high price, it was excluded from the project. This resulted in the
implementation of two types of film: 3mm and 6mm(3 beds per film type).
Materials used in the construction of all six low tunnels are listed below.
○ 1/2" PVC pipe 30­ 10ft pieces (hoops)
○ 3/4" PVC pipe 5­ 10ft pieces (hoop receptacles)
○ 2 X nylon rope 200ft
○ 3­mil Clear Overwintering Film (0.076 millimeter)
○ 6­mil Clear Overwintering Film (0.152 millimeter)
■ (1mm equals 0.0254 millimeters)
○ wood screws 200ct. box
○ 5/16"­18 x 2" Full Thread Hex Tap Bolts ­ 18​
pieces
○ Tools: electric drill, screwdriver, scissors, tape measure
It is worth noting that our construction methods were modified slightly from the
original plans we found. To secure the twisted ends of the film in place, rather than
using metallic components, we used a screws placed on the sides of the beds(one on
each side) as the anchoring points. Also, instead of wrapping the straps that hold
down the plastic film around a piece of rebar, we drilled holes in the hoop receptacles
and fed the straps through those holes. This was necessary, because, on the rooftop,
we could not insert rebar into the ground. However, this method was just as effective.
The procedure for constructing the low tunnels was relatively straightforward.
The following directions apply specifically to the approximately 8 ft by 4 ft beds that we
were working with, but can be easily modified for future projects involving different
dimensions.
To construct a low tunnel for one 8 ft by 4 ft bed,
1. Create hoop receptacles (Figure 3):
a. Cut 3/4" PVC pipe into 10 8­inch pieces
b. Drill two parallel holes in each 8­inch piece 3/4 PVC. Place one hole 1
inch from the bottom and the other 3 inches directly above the first hole.
Make sure to go through both sides of the PVC. Screws will be inserted
through these holes to anchor the hoop receptacles to the raised bed.
c. Drill another hole, between the first two holes(about 2.5 inches from the
bottom) perpendicular to the two existing holes, through both sides of
the pipe. The resulting holes will be used to anchor the nylon rope
straps.
2. Install hoop receptacles (Figure 3):
a. Orient hoop receptacles every 1.6 feet(distributed evenly), along the
long side of the bed (5 receptacles per side). Secure each hoop
receptacles, using two screws per receptacle, so that the end of the
pipe without the holes is level with the top of the bed( it should not stick
out above the bed). Feed the two screws through the two parallel holes
we drilled for this purpose. The hole for anchoring the straps should be
parallel to the side of the bed after the receptacle is attached.

5. i. Repeat for all 10 receptacles.
3. Create hoops:
b. Cut 1/2” PVC pipe into 7 ft pieces. Make 5 pieces for one bed.
4. Install hoops:
c. Bend the 7 ft piece of 1/2” PVC and feed each end through the two
corresponding hoop receptacles, creating arched hoops. Ends of hoops
should be resting on the screws that go through the receptacles.
i. Repeat for all 5 hoops
5. Cut the film:
d. Cut the film into a (approximately) 7 ft by 13 ft piece.
6. Install film :
e. Put film over the PVC hoops
f. There will be extra hanging off the sides. Twist these ends and tie them
off, so that film fits around the hoops as tightly as possible. (Figure 5)
i. Place 1 screw into each short side of the bed. Use rope to
secure each tied end to the screw on each side of the bed. This
secures the ends of the film to the bed and provides longitudinal
tension on the film.
ii. Feed the rope through the corresponding holes in the hoop
receptacles. Feed the rope through one receptacle, up over the
film to the other side and through the next receptacle on the
opposite side.
The rope should create a loop around each PVC hoop, holding
down the film about two inches lower than the hoop. (Figure 6) The two
end hoops will not have a loop, but a single piece of rope one one side,
facing into the middle of the bed. Do this for all pairs of receptacles(see
pictures in appendix to visualize this mechanism). This tension in the
straps holds up the film when lifted.
7. Install film­holding pins (Figure 2)
g. In order to prop up the film and make sure it doesn’t slide down due to
wind when lifted up, drill holes(through one side of the PVC hoop, at the
level where you want the film to be held when it is lifted up) for the “pins”
in the three middle hoops. The holes should be wide enough to
accommodate the pins, but shouldn’t be too loose, so that the pins don’t
fall out. Use the bolts as pins. To always make the pins easily
accessible, tie each pin to the corresponding hoop, close to the pin hole,
leaving some slack in the rope in order for the pin to hang off the hoop
when it is taken out. There are pins per bed, on the three middle hoops.
2. ​
Amending the Soil prior to seeding the Romaine Lettuce
1. Tested the soil texture­
We used a simple hand method, feeling the grittiness of the sand, then create
a moist ribbon of soil until it breaks. Then we cross referenced our findings with
the corresponding chart for deciding what type of soil we had. (Figures 7 & 8)

6. 2. Tested the soil pH.
We used Hellige Soil Reaction pH Tester Kits that only required the soil we
were testing. They were provided by the Tuchman Lab.
3. Tested levels of Macronutrients N, P, K
We used NPK Soil Test Kits that were also provided by the Tuchman Lab. The
only required supply that is not included is deionized water.
4. Added Compost
We first tilled and weeded the six beds. Then we obtained organic compost
from a local garden store. We used four 40 lb. bags per bed.
3. ​
Measuring the effectiveness of various greenhouse films​
.
To test the efficacy of the season extension structure we constructed as
accurately as possible, it was important that the growing conditions (besides the
season extension structures) were similar for all the of the beds. This will required that:
1. all raised beds received a similar amount of sunlight and shade
2. all raised beds received the same amount of water, administered at the
same time during the day ± 1 hour
3. all raised beds contain a similar soil mixture, with regards to nutrient
content(see appendix for soil testing data)
4. all raised beds are exposed to a similar amount of wind
■ This is especially important, considering the excessive amount of wind
on the rooftop, which will test the sturdiness of our structures
5. all seeds were planted on the same day, following the same planting pattern
in each raised bed, using a similar amount of seeds per square foot in each
raised bed as well as similar spacing between each plant
6. when unnecessary due to weather conditions, all structures were adjusted at
the same time.
At this time, as a part of comparing the effectiveness of the two greenhouse
materials, we have installed the two materials on all the beds and planted the seeds,
according to the guidelines described above.
However, at this time we were not able to obtain plant growth and temperature
data, because the seeds are yet to germinate. We have planted the seeds later than
expected because the construction of the low tunnels was more labor­intensive than
we anticipated and required more adjustment than we predicted. Our construction
plans also got delayed due to the long amount of time we had to wait for the films to
arrive in the mail. Furthermore, we had not anticipated having to amend the soil for all
the beds, which created additional setbacks for our project, since we had to amend the
soil before we could plant the seeds.
We have created a data table for recording the conditions that will assist in
comparing the effectiveness of the greenhouse materials we are testing. This plan
calls for a daily check­up on the structures, involving taking atmospheric temperature
inside and outside the low tunnels, measuring plant height, recording any
observations, and tending to the plants.Specifically the daily check­ups involve:

7.
1. Measuring soil temperature in each bed (at the center of each bed, at a
similar depth).
2. Measuring the height of 10 (randomly chosen) Romaine plants from each
bed and calculating a mean height for the 5 plants.
3. Watering the beds with an equal amount of water per bed, depending on
weather conditions
4. Weeding the beds (if necessary)
5. Collapsing/opening season extenders if necessary (weather­dependent)
6. Checking for damage to season extensions
7. Recording any other observations in a journal
Our plants, as of 28 April 2013, have sprouted. We have not been using the proposed
data sheet, but have been recording general observations and the number of plants in each
bed. This is because we are unsure if there will be a summer intern to continue collecting
data. The sheet is created and ready for the fall semester.The data and observations we
currently have taken are summarized in Figure 11.
2. Secondary goal: constructing low tunnels at the Winthrop Lot.
Unfortunately, we were not able to complete the main objectives in the proposed
amount of time due to unexpected delays as described above. This left us with no time
to construct additional low tunnels at the Winthrop Lot.
Results
Our group set out to build six experimental season extension frames, that are:
adjustable and reusable, efficient in extending the growing season, sturdy enough to
withstand windy conditions on the rooftop, and relatively inexpensive. We have successfully
constructed six season extension frames on each of the six plant beds that were provided for
us. Each season extension structure features a thin film that we have affixed in a way that
allows people to adjust the film on the PVC pipes (Figure 2). Through a simple mechanism,
each film can be fully or partially opened to allow ventilation inside the low tunnel. In the event
that any of the season extender structures needed to be removed and stored, the structures
were installed so that people could disassemble each pipe from the mounting attachments
(Figure 3). Since the season extenders have been installed, they have been able to withstand
the wind that flows through the rooftop garden. Additionally, each structure was fairly
inexpensive to construct (Figure 1).
Our group also set out to test the effectiveness of each greenhouse film material. This
was achieved when we developed a standard procedure to obtain the required data. We were
to plant romaine lettuce in all six beds through direct seeding techniques. In each bed two
rows of eight clusters each with three seeds per cluster were planted. This gave each bed 48
seeds.
We performed various soil tests that measured nutrient levels (nitrogen, phosphorus,
and potassium), pH levels, and labeled soil texture. As shown in Table 1​
, ​
beds 1­4 and 6 had

8. a sandy loam soil texture, while bed 5 had a loamy texture. In all beds, nitrogen levels
(“Levels of N” in the table) were low​
1​
. In beds 1­3 and 5, phosphorus levels (“Levels of P” in
the table) were low, while beds 4 and 6 showed optimum levels​
2​
of phosphorus. In beds 1 and
4­6, potassium levels (“Levels of K” in the table) were high​
3​
, while beds 2 and 3 showed
optimum levels of potassium. All beds had a soil pH of 8. As a result of this testing, we
amended the soil with organic compost to give a more favorable growing conditions to the
Romaine.
Our final goal was to construct more low tunnels for use in the Winthrop garden lot.
Here, we will leave it up to the caretakers as to whether or not this is necessary. We will
provide the same building instructions to assure consistent build quality with the original
season extension structures.
Objectives Accomplishments
Build six low tunnel structures for six raised
beds on the Quinlan Life Sciences Building
Rooftop Garden (Rosemarie Rochetta
Wessies Rooftop Garden)
Built six low tunnel structures for each of the
six beds on the Rosemarie Rochetta
Wessies Rooftop Garden
Design and execute an experiment to test
effectiveness of different greenhouse films
Designed experiment for testing the
effectiveness of the greenhouse films,
started to implement the experiment
Extend low tunnel structures to Winthrop lot Tested the pH and composition of soil as
well as macronutrients
Added compost to amend the soil
Discussion
The low tunnel structure was inexpensive and easy to build. The 8” pieces of the 3/4”
PVC pipe had two holes drilled into it and they were drilled into the sides of the beds as
holders. Then the 1/2” PVC pipe was cut into 7ft pieces which were then bent and inserted
into the holders. This process and installation only required a saw and hand drill. The cost of
materials for all the beds, not including the organic soil, was $217.99 which is relatively
cheap, especially since it did make six season extensions for 4ft by 8ft beds. The structures
are sturdy and stood up against several storms. One modification of the original design was
anchoring the films with extra rope after a few storms blew them out of place.
We designed our experiment to test the effectiveness of the different greenhouse
films. We decided to only use two different types of material because the third type was too
expensive. The experiment is started, and should continue to be monitored as stated in the
methods section. Romaine Lettuce was substituted for Kale because we found out that
Felice’s, a student run restaurant on campus, was looking for more local food, specifically
Romaine Lettuce for their salads. At the time of harvest, the plants of one bed should be

9. harvested and weighed together. The average weight of the Romaine Lettuce from three beds
using the 3mm greenhouse film will be compared to the average weight of the Romaine
Lettuce from the three beds using the 6mm greenhouse film to see if there is a significant
difference between the two averages. After being harvested and weighed, the lettuce should
be taken to someone​
​
at Felice’s.
We were not able to fulfill our secondary goal because we did not finish determining
which material was more efficient. The low tunnel structure and materials, however, are sturdy
and relatively inexpensive especially because they can be reused every year and are
removable as well as easily storable.
The cost effectiveness of the low tunnel systems as well as its ability to be attached to
a raised bed makes it practical for the average family, even in urban areas. It is also easy to
remove, store and is reusable, which is also a benefit. By testing the two materials and the
sturdiness of the structure itself we have helped to further season extension in temperate
climates where growing seasons are generally shorter. This allows more local produce for a
longer time which reduces the CO2 emissions and more nutrients absorbed by the fruit or
vegetable without use of chemicals.
During this project we learned how to build a practical solution to expand the short
growing seasons of the temperate climate and maximize urban space to grow more local
food. The low tunnels allow for a longer growing season. By using the rooftop garden we are
maximizing our limited space. We learned how to test soil to determine its composition, pH,
and macronutrient levels. Our low tunnel structures will be available for future students to use
on the rooftop garden. The instructions to build low tunnels will also be provided to students if
they wish to expand the structures to other campus agriculture sites such as the Winthrop
Urban Agriculture Demonstration Lot.
Conclusions
These low tunnel structures are easy to construct with very few materials and tools.
Very reasonably priced materials along with the structure being reusable makes it affordable
to the average family. The only modification is to make sure to tie down the film well so it does
not blow away. Also, do not leave only one side open because it will catch the wind and be
more susceptible to wind damage. Monitoring for damage is needed only after major storms.

10. Appendices
● Figure 1: Budget
Insert finances table here at the end when we’re done editing on Google Docs.
● Figure 2:​
​
Opened low tunnels​
. The holding pins are inserted to prevent film from
sliding down.
● Figure 3:​
Hoop receptacle attached to the side of the bed.

11. ● Figure 4:​
Installing the hoops.

12. ● Figure 5:​
Anchoring the ends of the film. The twisted ends should be tied off, then
anchored to the anchoring nails using rope.
● Figure 6:​
Anchoring straps. Tension in the anchoring straps should hold the film down
about two inches below the top of the hoops.

13. ● Figure 7­ Soil Texture Flow Chart

14. ● Figure 8­ Soil Composition Pyramid
● Figure 9 ­ Quinlan Rooftop Garden Plant Bed Soil Texture, Nutrient, and pH
Level Test Results

15. ● Figure 10: Proposed Data Table for Data Collection

16.
● Figure 11: Data Table Used
Bed / Material Plants Groups Observations
#1/ 6mm 32 13 Winds of 4/8 blew
down the plastic on
all four beds.
#2 / 6mm 29 11 4/10 Fixed the
plastic and added
end ties
#3 / 6mm 31 12 Winds on 4/8 blew
down the plastic on
all six beds.
Hypothesized that
it is because they
were left half open
and caught the
wind
#4 / 3mm 24 11 Bed #1 First bed to
show germination
#5 / 3mm 29 13 Overall all beds
had sprouted by
Sunday 4/28/2013
#6 / 3mm 32 15 All beds were
venthilated on 5/1
when outside
temperatures
reached 83 degrees
F

17. ● Figure 12: Before & After

18. Bibliography
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