Planning

Planning for a new greenhouse is one of the most important steps a grower will have to take. Proper site selection and location with relation to markets, labor, utilities and future expansion make the difference in how profitable the business becomes.

Certain decisions need to be made before a plan is developed. These will influence the location, type and size of greenhouses that are built. Basic information is needed. Start by answering the following:

• Crops to be grown - Bedding plants, potted plants, vegetables, perennials, herbs, etc.
• Growing period - year-round or seasonal.
• Plants to be grown in - pots, flats, beds, hydroponic troughs, etc.
• Growing media - soil, soilless mix, nutrient solution, compost, etc.
• Growing system - floor, fixed or movable benches, beds, growing bags, ebb and flood
• Annual production - How much growing space is needed?
• Marketing system - wholesale, retail or both.
• Investment capital available - $.

Although a greenhouse can be built on almost any site, some sites offer major advantages over others.

Consider the following:

Space - The area needed depends on the type of business, wholesale or retail. A minimum area should be about two acres to allow for the greenhouse, parking for customers and employees, access driveway for deliveries, storage and future growth. A wholesale operation generally requires more area because more greenhouse space is needed.

Zoning - These local regulations control the use of land and promote health, safety and welfare of the community. Greenhouse operations can only be located in certain zones. Frontage, side yard distances, signs and the number of parking spaces are frequently specified. A check with the zoning enforcement officer should be one of the first steps taken. At the same time inquire about building codes to see whether a permit is needed.

Highway Access - Location with respect to highways should also be considered. For a retail operation, a location on a high traffic count road or near a large residential area can increase business. For a wholesale business, access to an interstate highway is desirable to handle heavy truck traffic.

Property Values - The cost of a piece of land can add a significant debt load to the business. Location for retail purposes is more important than for a wholesale operation. Inspect several sites before making a choice.

Environmental Concerns - Care should be taken to pick a site away from industrial pollution. Beside plant injury from pollutants, light levels may be lower in these areas due to smog.

Climate - Areas with temperature extremes should be avoided. Because plant growth in the winter is directly related to the amount of light received, avoid areas that are noted for their cloudy weather. The potential for high winds, heavy snow and hail should be determined before site selection is made.

Slope - The functional and environmental separation of a greenhouse can be affected by the building site selected. Ground slope for drainage of water is important. Greenhouses should be placed on a gravel base, 6" to 12" above grade. Swales between greenhouses are necessary to direct the water from the area.

Drainage - Property with limited wetland is desirable as regulated areas may be 150' from the edge of the wetland. Obtain a topographic map of the area to see where the water will drain. A permit may be needed to drain onto neighboring property. In larger installations, culverts down stream may have to be enlarged to handle the extra water collected from greenhouse roof surfaces and parking areas.

Orientation - The ideal site would have a slight southerly facing slope for good winter light and protection from northerly winds. The area for the greenhouses should be level to reduce materials handling costs. It generally pays in the long run to spend a little extra on site preparation to get the site level.

Water - Plants require an adequate supply of moisture for optimum growth and maximum flower production. The amount of water needed will depend on the area to be watered, crops grown, weather conditions time of year and the environment control system. For most of the U.S. , a maximum summer time requirement is about 400 gallons/square foot/watering.

All water from natural sources contains some impurities. Some of these adversely affect plant growth. Chemical tests should be made by a testing laboratory and the results analyzed by Cooperative Extension horticultural agent.

Electricity - An adequate electric supply and distribution system should be provided to serve environment control and mechanization needs. Early in the planning process, contact the electric utility about the availability of power and the best location for the service drop. Once this is done a plan for the distribution system can be developed.

Expansion - All through the planning process, provisions should be made for expansion. What will the operation look like in five or ten years? Land should be available for additional greenhouses and parking. Water, electrical and environment control systems should be installed with expansion in mind.

Labor supply - Additional labor, full or part time, may be needed as the business grows. The location can influence the size of the labor pool form which it can draw and the type of skills local employees may possess.

Greenhouse Selection

Greenhouses for commercial production can be classified as free-standing or gutter-connected.

A free-standing greenhouse can have a quonset (hoop), gothic or gable roof shape. The quonset is usually the least expensive and is available in widths to 34'. Gothic designs have higher light transmission and shed snow easier. Gable designs may use trusses to span a width up to 60'.

A gutter-connected greenhouse is a series of trusses connected together at the gutter level. Individual bays vary in width from 12' to 25' and have a clearance of 8' to 16' to the gutter. Bays can be put together to get any width of greenhouse desired.

Greenhouses can be made any length. Standard lengths that utilize glazing materials to advantage are 96' and 144'. All greenhouses are modular with frame spacing of 4' or 5' for hoophouses and 10' or 12' for gutter-connected designs.

Most greenhouses are built of galvanized steel tubing and are available from many manufacturers throughout the U.S. Steel makes a strong frame to carry snow and wind loads and still allow about 80% of the light to enter.

Most greenhouses are covered with a plastic glazing. Low-cost polyethylene applied as an air inflated double cover will last 4 years. Anti-drip agents and infra-red inhibitors are added to give better service and reduced heat loss. Semi-rigid structured sheets of polycarbonate or acrylic are more permanent and have a life of at least 15 years. Tempered glass is used for crops requiring a high light levels.

The following is a short review of the advantages of the different styles of structures:

Free-standing Greenhouses

• Usually the best choice for the small grower planning on less than 10,000 sq ft of growing space. You can start with one house and add more as the business grows.
• Easier to provide separate environments as each house is controlled by its own heating/cooling system. One house can be run warm for propagation and the next one, cooler for growing.
• Individual houses can be shut down for periods when not in use. Gutter-connected houses are generally heated year-round.
• Best suited for heavy snow areas as multi-span houses need heat to melt snow from the gutters.
• Good for non-level sites.
• Individual houses are easier to build and maintain.
• Less expensive to build. Site preparation and erection costs are less.
• Expansion of growing area is easier without disturbing plant production.

Gutter-connected Greenhouses

• More cost effective for areas greater than 20,000 sq ft.
• Reduced heating costs as surface area to floor area ratio is less. Heating costs can be as much as 25% less due to reduced glazed area.
• Less land is needed. About 30% more growing space can be placed on the same amount of land area.
• Greater labor efficiency. Carts and conveyors can be easily adapted as everything is under one roof. Moving bench and tray systems also adapt more readily. Better labor control.
• Utilities are easier to install. Electrical service and water supply are centralized making installation and maintenance easier.
• Heat can be centralized. A single boiler is easier to install and maintain.
• Open-roof designs that eliminate fans and reduce cooling costs are available.
• Easier to adapt to computer environment control. Installations costs are less.

John W. Bartok, Jr.
Agricultural Engineer
Natural Resources Mgt. & Engr. Dept.
University of Connecticut , Storrs CT

May 2005