San Pablo Community Nursery

Welcome to the San Pablo Community Nursery


What are we all about?

Working with the village of San Pablo, Guatemala, Cal Poly students from all majors have been involved in advancing appropriate technology and collaboratively working towards increasing knowledge and development for both the people of San Pablo as well as the Cal Poly students. One of the potential areas for investigating and possible development that was found in San Pablo was that of a community nursery in which the people could grow their own seedlings. Currently, in order to purchase the seedlings, people must travel out of the village into the nearby city. A community nursery run by the local people and cultivated with care could provide an abundance of seedlings for the locals. This would alleviate travel costs and time and could even generate revenue for the community. Furthermore, the project nursery group will be collaborating with the Entrepreneurship Group (Entrepreneurship groups website) to create a business plan that can be given to the San Pablo residents as a guide to start up the community nursery business.

Background Information San Pablo

Weather Conditions

San Pablo is fairly close to the ocean and has an altitude of 2800 meters above sea level. It is in a very tropic area an has a rainy season that lasts from mid-May to late October or early November. The typical temperature range is about 12-15 degrees C during the day with night temperatures usually staying around the same with some extreme cases of 20 degrees C during the day. During the cold season however the night time temperatures can drop to below 0 degrees C for long periods of time.

Problem Statement
San Pablo residents are purchasing seedlings from nearby villages for growing personal crops. Our innovation is needed to minimize costs to San Pablo residents as well as create a educational, sustainable business that will grow over time.

Create a greenhouse nursery where the San Pablo residents can cultivate crops like tomatoes for home use. Eventually they might even be able to export their crops.
We have completed a lot of research that will keep the creation of this greenhouse and business costs very low to the residents. Some of the research that we have found is planting deciduous trees around the greenhouse that will insulate the green house. We have thought how we can obtain maximum sunlight 365 days of the year, and the ‘green building materials’ that can be found in San Pablo.

Project Scope


The location is the first point to take into consideration when planning the construction of a greenhouse. Depending on the dimensions of the greenhouse, space can be a constructive challenge as well as getting proper sunlight. The location of a greenhouse should be situated the receive the maximum amount of sunlight during both summer and winter. The winter sun is lower than the summer sun, so planning ahead helps avoid sunlight issues in the future. Furthermore, if the greenhouse exceeds the wanted amount of sunlight during the summer months, additional shade will have to be provided to let the plants get a rest from the suns rays.

The town of San Pablo lies in a slopey terrain. We can use this to our advantage if the slope faces the rise and set of the sun. By constructing the greenhouse on a slope, we eliminate a wide area of the the heat retaining plastic, which reduces the chance for heat to escape the greenhouse. This may or may not be an option for construction but would be the best suited for the needs of our greenhouse.

Greenhouse Covering Materials

There are a number of options that we could use for covering the greenhouse. Economically, we can rule out such coverings as glass and fiberglass; they are just too expensive for the locals of Guateca. The cheaper options are film plastic and Double-wall plastic. They each have their advantages and disadvantages but the Double-wall plastic has a key feature that sets it apart from the Film Plastic. The Double-wall is a rigid structure with double layers of acrylic or polycarbonate separated by webs that give long life (up to 10 years) and retain heat within the greenhouse. This is a key point for the area considering temperatures reach freezing at night. The constraint with double-wall plastic is that 10% of the heat is lost with each layer. Therefore, only 80% of light is getting through the plastic.

Foundations and Floors

After some reserarch, we have come to what we think to be the most economically suitable, strongest, and best heat retaining foundation and floor. The average dirt stays a temperature around 55 degrees down to three feet below the topsoil. By digging the greenhouse into the ground, it is protected from wind that would normally threaten a greenhouse that was not dug into the earth. Additionally, a large area of the double-walled plastic on the sides of the greenhouse will be eliminated which reduces the chance of heat loss. We will use old tires filled with dirt or black barrels filled with water to support the greenhouse walls. These materials will reduce budget costs while being environmentally responsible. The tires and barrels are used on the sides of the excavated greenhouse to support the skeleton of the double-wall plastic. The tires and barrels will also attract heat from the sun and retain it, keeping the greenhouse warm through the cold nights.

The greenhouse foundation

A great attribute about digging the greenhouse into the ground is that there are virtually no constraints to the design besides the extra labor to excavate the hole. And since the plants are place above the ground on shelves, no direct sunlight to the plants is lost.

A low-cost, practical floor will be as simple as using several inches of gravel instead of concrete. The gravel can also be used for drainage of excess water. With this system, water can be sprayed on the gravel to produce humidity within the greenhouse if needed. A walkway of concrete or other big stones is recommended for ease of access to the plants.


It is required of the caretaker to the nursery to manipulate and maintain a sustainable environment in the greenhouse. This is done by using heaters, fans, thermostats, and other equipment. Several attributes to our greenhouse mentioned already will reduce heat reduction. But for those really cold nights in San Pablo, an extra layer of insulation might be needed to ensure the safety of the plants in the greenhouse. A cover that can be pulled over the greenhouse is a simple solution that will keep the warmth from escaping. We would prefer to find a cover in the local area that is a material of no use to anybody. A lot of materials can be used for this cover, as long as it is semi-thick but not so heavy that it threatens the instability of the greenhouse.

Air Circulation

During the winter months, air circulation can become a factor. Without a circulation system, hot air will rise to the top of the greenhouse and cold air will settle at the bottom. This thermal convection can be dangerous for the plants. A much faster and even circulation system must be created. Fans placed horizontally from each other can achieve such a uniform temperature that we are looking for.


Ventilation is a simple idea to understand. It is needed during the summer months in order to exchange hot air for cold air, cold air for hot air, remove the moisture, and replenished vital carbon dioxide. Roof vents allows for the warm air to escape from the sides while sucking in cooler air from side inlet vents.

Sample drawing of greenhouse
Since the San Pablo terrain has many hills and mountains, it would be to our advantage to dig out the greenhouse on the side of the hill, facing the rise and fall of the sun. This would eliminate some of the area which is vulnerable to heat loss as well as save some money on materials
This is a sketch of a prototype that will be used to heat the plants. The black barrel will attract heat which will warm the water inside. The water will run downward through a zig-zag pattern beneath the plants to keep them warm. The water will run through a continuous cycle and this system will require little to no maintenance.

Cost Analysis of Greenhouse
This is a table displaying our projected cost of the greenhouse. It is strictly estimations from sources based on prices in the United States. The prices of these materials might vary differently in Guatemala and some of the categories listed may or may not have to be implemented in the final greenhouse design.

Approximate cost of constructing a 28-foot by 95-foot double-layered polyethylene, quonset-styled greenhouse (2,660 sq.ft.) Cost in U.S. dollars
FrameFrame bows (steel tubes) with 5-foot spacing. 2,320 , 0.87 sq ft
Cover layers of 6-mil polyethylene (3-year life)Attachment apparatus 515360
End WallsPolycarbonate sheet and frame (10-year life)One welded aluminum front door (4 ft by 8 ft) 1,665 , 0.63 sq ft190
Heating System (if needed)Gas unit heater (225,000 Btu)Assorted heat equipment with control panelAn overnight cover (recycled) 6655400-100
FloorOld Recycled Tires or BarrelsPlastic for ground cover (3oz/sq. ft.)Gravel,13 tons, delivery extra 0180145
Power and Utility SourcesBasic irrigation hookupsElectrical service 200450
BenchesCoated wire–14 gauge, 1-inch gridTreated lumber frame, 2-inch by 4-inchCinder block legs 1,090575185
Cooling and Ventilation SystemsFour horizontal air flow fansAssorted fan and vent equipmentPower vent (5 ft by 15 ft) 375145935

The total estimated cost of a greenhouse will be approximately 10,635 U.S. dollars. This estimation excludes labor for installation.

Plant Type
The main crops grown and utilized in San Pablo include potatoes and tomatoes. The village has already found a successful method of starting potato plants, through quartering whole potatoes and planting them. However, they lack a similarly successful manner of starting tomato plants. Currently, the village’s people travel out of town to obtain tomato seedlings, wasting both time and money. Thus, the focus plant of this project is the tomato plant.

The basic needs in regards to cultivating the tomato seedlings include containment, nutrition, and water. The seedlings can be housed in various items. For instance, a more tailored option is what is termed a seed pod. A seed pod is a mesh casing that is filled with nutrient rich starter soil. The seedlings can germinate in the pods then the whole containment system can be transplanted into the ground to develop into a full-grown tomato plant. This is due to the fact that the pods are environmentally friendly and biodegradable. They will break apart naturally once the roots of the seedlings spread. An additional method of cultivation includes planting the seedlings in a rectangular slab of soil and then dividing the soil slab into numerous squares, each containing a seedling. This is simple approach to separating the seedlings and would require the use of a cutting device, whether metal, plastic, or cardboard. The soil cubes are then transplanted into the ground when ready. Using this method, the soil around the seedlings is less contained and compact. For more structure, boxes or plastic pots may be utilized. These allow for the soil to become slightly more compact. The roots must be loosened before transplantation with this method of containment. All containment methods previously listed will be effective in producing seedlings, yet they vary in the mode of transplantation. Seedlings in general require specific nutritional soil as opposed to plain ground soil or top-soil. Once they have grown enough for transplantation, they can be put in less nutrition rich soil. In regards to hydration, they seedlings need to be watered regularly. Thus, access to a steady water source is essential for their successful growth.

Growth Requirements
Tomato seedlings require a somewhat extensive amount of tender care. The various areas in which they must be closely monitored include temperature, hydration, light, and nutrition. Tomato seedlings, as well as whole plants, require the temperature in their environment to remain relatively constant during their growth and development. Their preferred temperature range is from 65 to 70 degrees. Thus, a sealed and regulated external environment is necessary to house the seedlings. Regulation from this temperature range will stunt growth and cause a lag in the normal growth time of approximately one to two weeks. In order to produce a successful yield of seedlings, it is imperative that the temperature be maintained.
Tomato seedlings require varying degrees of hydration during their growth and development. In the initial stage after planting the seeds, they should be watered moderately, avoiding soaking the soil. It is essential that the seeds do not receive too much water when they begin to germinate. After this initial watering, they should be kept hydrated and the soil should be saturated.
Varying amounts of sunlight (or artificial light) can be shone on the plants, with those varying levels of light determining the rate at which the seeds germinate and grow. In order for seedlings to grown within one to two weeks, they prefer to receive between fourteen and sixteen hours of light a day. Less light, to a certain extent, will still allow for successful growth, however, the time in which they grow will be slowed down. Instead of happening within one to two weeks, seedlings may take three to four weeks, or longer, to grow. An artificial light source may be utilized during the growth of the seedlings. However, this method either requires the use of the grid, or the obtaining of solar panels to power the electric light source.
As mentioned briefly earlier, seedlings require nutritious soil during the early stages of their cultivation in order that they develop properly. Simple ground soil or potting soil will not provide enough nutrition for the plants, due to the fact that they are low in nitrogen content, an element essential to the success of any crop. Thus, soils rich in nitrogen, phosphorous and other essential elements must be used to initiate seed growth.

Recycling unwanted materials
Our mission in designing a community nursery is to benefit the village as much as possible. We would like to both save the people time and money, as well as potentially clean up the community. Thus, it is a mission of ours to use materials that are already prevalent in the village itself. This would help eliminate garbage and waste around the community while fostering the mentality of the importance of using all materials creatively. Old plastic water bottles can be cut and used for seed containment as well as egg cartons. To mimic the nature of the mesh-like seed pellets, old tee shirts may even be used to contain the seedlings. The availability of any of these such materials, or similar materials, will allow us to truly utilize the materials already present in the village for brand new purposes.

The main materials, in regards to the cultivation of the seedlings, to be purchased include the containers, soil, and seedlings themselves. In regards to the containers, seed pellets, complete with their own nutritious peat moss soil, can be purchased for approximately $0.12 per pellet. If instead, there are materials suitable for recycling into seedling pots, then the cost for containment will be minimal to non-existent. However, then a nutrient rich soil type will also need to be purchased. Soil suitable for seedling growth costs around $7 for a bag that contains 9 quarts of soil. The seeds themselves vary in price depending on specific tomato type. They range from $1-4 per container of approximately 30 seeds. The total cost of supplying the initial seedlings and other growing materials depends on the size of the greenhouse created but can be calculated using these approximate numbers.

Materials Cost (U.S. dollars) Benefit Drawback
Soil Pellets $0.12/pellet biodegradable accessability
Soil Cubes N/A made purely from soil need to break apart roots
Plastic bottles/egg cartons free if made from trash readily available toxic to environment
Peat pots $6.00/30 pots easy to use accessability
Plastic pots $5.00/12 pots easy to use accessability
Clothing free if made from trash readily available may not break down like pellets

Team Bios


Kyle Sato — Team leader
Focusing on project development and communication with collaborating groups. Senior Forestry and Natural Resources Major California Polytechnic State University, San Luis Obispo


Brecken Thomas — Head biologist
Researching ways to cultivate greenhouse plants. 4th year Microbiology major, California Polytechnic State University, San Luis Obispo


Matt Griego –Historian/Communicator
Researching the history and background information of San Pablo. Communicating with people that have been to San Pablo as well as other informational sources. 4th year Mathematics major, California Polytechnic State University, San Luis Obispo


Travis Cook — Lead Architecture
Designer of the Greenhouse. Researching low cost, ‘green’ building materials. Architecture Junior at California Polytechnic State University, San Luis Obispo

Grant Proposal

Works cited