A Greenhouse Garden for Sichuan
A Greenhouse Garden for Sichuan
By Peggy Bradley
In May of 2008 a terrible earthquake shook areas in Sichuan. After tremendous loss of life, and one million families made homeless, the people of this area are ready to begin rebuilding their homes and their lives.
The rebuilding of homes will require new forms of architecture that will remain strong in the event of a future earthquake. They also need to be more energy efficient. Improved housing is possible for the people affected.
Thanks to simplified hydroponic’s intensive food growing technologies, the production of healthy food is possible and is available a lot sooner compared to growing produce in traditional gardens.
Simplified hydroponics is the technology of adding plant nutrients to the plants water supply. The nutrients can be chemical based fertilizers or organic nutrients. Usually in simplified hydroponics, plants grow faster and produce more foods than soil based gardens.
In the case of Sichuan, a garden is proposed for an attached greenhouse to grow some fresh foods year round.
For a greenhouse garden to be successful, it will have to be facing the southern exposure, and have access to full sun during the day. This means sunlight must be available from at least 10 a.m. to 4 p.m. with no shading. While some of the vegetables need some shade, most require a portion of full shade each day. If this amount of sun is not available, the plants are likely to suffer.
Winter sunspace is more complicated because the sun rises lower in the southern sky. So trees or other obstructions that are not evident in the summer show themselves in winter. So it is important to start with a site sun map that allows for both summer and winter exposure on the southern side of the new dwelling. This is also important for solar collectors for solar heating and cooling.
Vegetables to Grow
Every family will have their own preferences for foods they would like to grow. Most vegetables have been successfully grown in hydroponics, and in greenhouse culture.
A recommended space for family vegetables is 200 square feet. This amount of space can produce about 75 ounces of vegetables a day.
This growing space can be combined with a passive solar addition to a home to be an energy efficient method of heating and cooling the home. The hydroponic growers can be filled with solar collectors such as gravel and water. A solar cooker can also be included to create a living space that helps produce family foods.
For the Sichuan garden the following plants are chosen as likely favorites for several families: ginger, scallions, bok choy, Sichuan chili pepper, garlic, cucumber, celery, salad greens and tomatoes.
A good size of this year round growing space is 10 feet by 20 feet. The glazed area of this space is likely to be 200 square feet of glazed space requiring 200 gallons of water as the heat sink storage space. These 200 gallons should be on the south facing wall, exposed to the daytime sun. 25 gallon storage containers should be enough and the best shape is in cube shaped five gallon black plastic containers.
The water containers should be black plastic and located against the interior southern facing wall. They are used to collect rainwater and supply a heat sink for the excess solar energy. The 200 gallon is a minimum, and 500 gallon is the maximum for these containers.
If the greenhouse is properly designed and maintained, it can collect 220,000 BTU per day, as much as in 47 pounds of oak, 220 cubic feet of natural gas, or 1.5 gallons of fuel oil. This energy requirement is estimated as a daily cost savings of $7.50 a day.
The solar greenhouse can be made of locally available materials at a relatively low cost. To also be a solar collector for providing heat, the greenhouse space needs to be designed so that the winter sunlight is collected on the rear water tanks, so the front table grower must be lower to the ground and grow shorter vegetables. The back grower above the black water tank can grow anything so larger plants are reserved for that area. The greenhouse includes several growing areas, a composter and a solar cooker. The composter is necessary to provide some warmth and CO2 for the plants.
The expected daily output in vegetables is about 75 ounces a day. These numbers are generally correct based on experiments and literature. The actual output can be more or less depending upon management, species grown and greenhouse management. This amount of vegetables can be estimated at costing about US$10.00 a day.
The solar greenhouse should also include a solar stove. There is a wide variety to choose from, and two or more in the greenhouse can assist in daily food preparation. The solar stove can include a solar food dehydrator, and a small space under the support for a wood fire if needed on very cold days. The wood fire option requires venting of smoke out of the greenhouse.
With the solar greenhouse heating the home and the solar stove used for some of the cooking, the need for firewood should be reduced for the family.
To prepare a solar green house for Sichuan, experimental models should be built in the area to access costs of site preparation, construction and daily operation. Plant production can also be tracked and costs of nutrients and water can be evaluated. A model greenhouse adapted to the area’s climate conditions and available materials should be designed and built.
Daily water requirements for hydroponic culture varies according to environmental conditions, age of plant and type of substrate used, but it can be generally predicted that each square foot will require about 1/10th gallons.per day of water, so this greenhouse garden will likely use about 16 to 20 gallons of water every day. Assuming water storage of 500 gallons in the greenhouse, the storage should be enough for 25 days of greenhouse production.
Water can be conserved in the greenhouse if irrigation of the plants is below the surface of the substrate and if the substrate is chosen to reduce surface evaporation. If the daily transpired water could be partially recaptured in nighttime condensation, the water use might be reduced even more.
The plant nutrients can be provided by organic or inorganic sources. The actual requirements of nutrients should be about three or four grams of minerals. If this is supplied in inorganic fertilizers it should be about 15 grams of material and if supplied in organic should be about 150 to 300 grams of material. The amount and cost of plant nutrients will vary but should be just a few cents a day for inorganic and at no cost or expensive if organic.
In the wake of the recent earthquake, this simple structure can be examined as a method to reduce individual family energy requirements in the future. The solar greenhouse addition can utilize solar energy to reduce home heating costs, reduce fuel requirements for cooking and reduce energy requirements in obtaining and storing food.
There are added benefits in food security for the family and high quality vegetables that should provide a health benefit.
Institute of Simplified Hydroponics offers to collaborate with Sichuan University in adapting this technology to the earthquake-affected regions.
Article Courtesy Maximum Yield Publications Inc.
Bradley, Peggy, “A Greenhouse Garden for Sichuan”, Maximum Yield’s Industry News, May 2008, pgs 34 and 36.