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Agriculture Information Bulletin No.357 U.S.DEPARTMENT OF ñCQ' m: ARV BvíMíM

So you've finally decided to get You can get 1 the most green- that hobby yoiCte al-i i house for your money by doing ways wanted. some of the construction work The first thing you have to do yourself. How much work you do is make a couple of decisions: depends on how handy you are How much money do you want to with tools. Be honest with your- spend? How much work do you self—don't take on a job that's want to do? too big to handle. A hobby greenhouse can range If you are good with tools, from a simple polyethylene cov- you can put up any plastic cov- ered framework that you can ered greenhouse, and almost any put together in an afternoon for prefabricated glass greenhouse. less than fifty dollars to a six- You'll have to hire a qualified thousand dollar fully automated electrician and plumber. conservatory. No matter which size or type of greenhouse you choose, con- TYPES OF sider how much time you'll have There are two basic types of to spend in it after it's built. greenhouses: attached and free Don't be over enthusiastic ; some standing. An attached green- new greenhouse owners find house may be even-span, lean-to, they do not have as much time or window-mounted. A freestand- as they thought for gardening. ing greenhouse is usually even- On the other hand, there is a span (symetrical roof). misconception that greenhouses require constant attention. By Attached Lean-To combining automatic controls and easy-care , mainte- A lean-to greenhouse is built nance can be kept to an hour a against a building, using the ex- week. Automatic controls are isting structure for one or more ideal for providing proper grow- of its sides. It is usually attached ing temperature, artificial light, to a house, but may be attached watering, humidity, and ventila- to other buildings. tion. Or if you have time, you can The lean-to is limited to single save a lot of money by not using or double-row benches with automatic controls. a total width of 7 to 12 feet. It PN-2698 Curved eave, slant side glass-to-ground lean-to greenhouse with roll-up slat shades and fin tube radiation heat.

can be as long as the building it accommodate two or three rows is attached to. The advantage of of plant benches. the lean-to greenhouse is that it The cost of an even-span usually is close to available elec- greenhouse is greater than the tricity, water, and heat. cost of a lean-to type, but it has The lean-to has the following greater flexibility in design and disadvantages : provides for more plants. • Limited space. Because of its size and greater • Limited light. • Limited ventilation and tem- COST perature control. The lowest cost per square foot Attached Even-Span of growing space is available in the even-span greenhouse 17 to The even-span greenhouse is 18 feet wide. It will house two the standard type—the one peo- side benches, two walks, and a ple generally visualize when they wide center bench. think about a greenhouse. The lowest total cost green- The even-span greenhouse is house is the lean-to house 7 to similar to a free-standing struc- 12 feet wide with double-row ture except that it is attached to benches and a central walk. a house at one gable end. It can

« amount of exposed glass area, Free-Standing the even-span greenhouse will The free-standing greenhouse cost more to heat. is a separate structure and con- sists of side walls, end walls, and Attached Window-Mounted gable roof. It is like an even-span A window-mounted greenhouse except that a free-standing will allow space to grow a few greenhouse is set apart from plants at relatively low cost for other buildings to get the most heating and cooling. This reach- sun. It can be made as large or in greenhouse is available in small as desired. many standard sizes, either in A separate heating system is single units or in tandem ar- necessary unless the greenhouse rangements for large windows. is very close to a heated building. Only simple tools are needed to The free-standing greenhouse is remove the regular window from more easily adapted to the build- the frame and fasten the pre- er's ideas of location, size, and fabricated window greenhouse in shape than attached greenhouses. its place. It also provides more light, but

PN-2700

This 10 foot wide lean-to has ample room for two 36 Inch wide benches along each wall. Glass shelves and hanging baskets may also be installed. {Photo courtesy of J. A. Neorrng Co./ Inc.) " " ' ' " PN-2699

A free-standing greenhouse is set apart from othter buildings, witli a door at one end (or a door in both ends for long units). (Photo courtesy of Lord 8. Burnham) requires more heat at night due where it will be partly shaded to the additional glass. during the summer when light re- duction is not serious and may be LOCATING YOUR desirable. Be sure to take into GREENHOUSE account the possibility of falling limbs that can damage the green- After you have decided which house. kind of greenhouse you want, you will need to determine where Some plants will grow in a you are going to put it. greenhouse in any location. The first choice for a green- African violets and orchids, for house site should be on the south example, will grow with northern or southeast side of the house in exposure—but heating costs will a sunny location. The east side be high. You will limit the types is the second best location. That's of plants you can grow if you where it will capture the most don't put your greenhouse in the November to February sunlight. best possible location. The next best locations are the Sometimes you can place a southwest and west. The north greenhouse against a door, win- side is the least desirable loca- dow, or basement entrance of tion. your house. This will let you use You can place your greenhouse heat from your house to grow walks. Allow approximately 6 LOCATION inches for walls at either side An ideal site for your green- and 2 inches for an air-circulation house would be one that is well- space between the side walls and drained, nearly level, and has full the benches. exposure to sunlight. It would Side benches are serviced from slope slightly to the south and only one side and should be no have a windbreak on the side of wider than you can reach across. the prevailing wind. For some people this will be 2 feet, for others perhaps as much as 3 feet. plants, make your greenhouse Center benches are serviced more accessible, and save on con- from both sides and can be as struction costs. Your home heat- wide as 6 feet. They should be no ing bill, however, will increase wider than to permit you to work significantly. comfortably. If you have an L-shaped house, Determine the width of the you can save the cost of two walks in your greenhouse by how greenhouse walls by building the they are to be used. If the walks greenhouse in the "L". will be used only as a place to Whether your greenhouse runs stand while servicing the benches, north and south or east and west an 18- or 19-inch walk is suffi- is not as important as wind pro- ciently wide; if a wheelbarrow tection. Protect your greenhouse will be brought into the green- from winds by locating it so ex- house, the width must be greater. isting buildings will shield it, or Wide walks—24 to 30 inches— by providing it with a windbreak will allow easy passage for visi- hedge or fence. tors who may not be used to walking between rows of plants.

DESIGNING YOUR Greenhouse Length GREENHOUSE Determine the length of your You will need to determine the greenhouse by multiplying the exact dimensions for your green- number of plants you can grow house before you start to build. across the benches by the num- Width is the most important ber of plants you want to grow. dimension ; it will not be changed Then round off the measurement during the life of the greenhouse. so that no glass will need to be Length can be increased if more cut to fill odd sash bar spacings. space is desired. (A sash bar is a shaped wooden or metal bar used in the construc- Greenhouse Width tion of a sash or frame and de- Determine the width of your signed to hold and support the greenhouse by adding the widths glass secure to it.) of the plant benches and the Standard glass sizes are 16 by

6 24, 18 by 20, and 20 by 20 inches. TYPES OF CONSTRUCTION (Larger glass sizes means few sash bars and less shadow inside Whether you build a glass, the greenhouse.) Most plastics fiberglass, or plastic greenhouse, are available in 100-foot lengths. it will pay you to shop around for When you figure the length of ideas. a glass greenhouse, allow for the Greenhouses have supporting width of the projecting part of framework made of wood, alu- each sash bar plus a fraction of minum, iron, or galvanized pipe. an inch clearance. For plastic, Some have curved eaves; others allow an extra 24 inches to fasten have flat eaves. Some are glass or the plastic properly. plastic from the ground up. All types have advantages and dis- Greenhouse Height advantages. The height of the greenhouse If you build your own green- depends on the desired height to house, have the plumbing and the eave. An eave height of 5 electrical work done by profes- feet is satisfactory for side sionals in accordance with local benches with low-growing plants. codes. Most local governments If you want to grow tall plants, require a building permit to erect however, you will want an eave a greenhouse. height of 6 or 7 feet. The pitch of the roof should Glass Greenhouse be 6 in 12 (approximately 27 de- Glass is the traditional green- grees). The eave height, the dis- house covering. It is available in tance from the side wall to the many designs to blend with al- center of the greenhouse, and the most any style or architecture. roof pitch will determine the Glass greenhouses may have height of your greenhouse at the slanted sides, straight sides and center. eaves, or curved eaves. The height of the greenhouse Aluminum, maintenance-free should be equal to the eave glass construction has very pleas- height plus one-fourth the width ing lines and will provide a large of the greenhouse. growing area. It assures you of a For instance, in an even-span weather-tight structure, which greenhouse 18 feet wide, the dis- minimizes heat costs and retains tance from the side wall to the humidity. center of the greenhouse is 9 For amateur gardeners, small feet. The difference in height prefabricated glass greenhouses between the center of the green- are available for do-it-yourself house and the eave will be one- installation. They are sold in dif- half of 9 feet, or 41/2 feet. If the ferent models, to fit available eave is 5 feet high, the green- space and to fit your pocketbook. house should be 9% feet at the The disadvantages of glass are center. that it is easily broken, expen- sive, and requires a much better • Construction cost per square type of construction than fiber- foot is generally one-sixth to one- glass and plastic. tenth the cost of glass green- houses. Fiberglass Greenhouses • Plastic greenhouses can be heated as satisfactorily as glass Fiberglass is lightweight, greenhouses. strong, and practically hailproof. • Crops grown under plastic Corrugated panels 8- to 12-feet are of equal quality to those long and flat fiberglass in rolls grown under glass. are available in 24- to 48-inch • Plastic greenhouses are con- widths. Thicknesses range from sidered temporary structures and %4 to %2 of an inch. usually carry a low assessment Poor grades of fiberglass will rate for tax purposes, or may not discolor and the discoloring re- be taxed at all. duces light penetration. Using a Plastic greenhouses can be good grade, on the other hand, made of polyethylene (PE), poly- may make your fiberglass green- vinyl chloride (PVC), copolymers house as expensive to build as a of these materials, and other glass one. If you select fiberglass, readily available clear films. choose the clearest grade. Do not Polyethylene must be replaced use colored fiberglass. " ' " " each year ; it deteriorates rapidly Plastic Greenhouses Plastic greenhouses are in- creasing in popularity. The rea- PLANS AND DRAWINGS sons are: Plans and drawings for plastic greenhouses and propagating frames are for sale by the Super- intendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, your State Agricultural Experiment Station, county agricultural agent, or the extension engineer at your State University. If you do not know the location of your State university, send your request to Agricultural En- gineer, Extension Service, U.S. 1171K406-16 Department of Agriculture, Greenhouses come in a number of types, styles, and sizes. For the handyman, a plastic Washington, D.C. 20250. He will tri-penta greenhouse can provide do-it-yourself forward your request to the cor- satisfaction. USDA Plan No. 6097, "Tri-Penta Greenhouse" is available from your State rect university. university. t in the strong sunlight of summer. Polyvinyl chloride (PVC or Vinyl) Other films such as PVC or co- Vinyls from 3 to 12 mils thick polymers with ultraviolet (UV) are available for greenhouse cov- inhibitors last longer. Descrip- ering. Like polyethylene, vinyls tions of plastics available for are soft and pliable; some are covering hobby greenhouses are transparent, others transluscent. provided below. They are usually available in 4- to 6-foot widths only; larger Polyethylene widths can be made by electroni- The advantages of polyethy- cally sealing several smaller lene are that it is low in cost and widths together. lightweight. It also stands up well Vinyls cost from two to five in fall, winter and spring weather, times as much as polyethylene. and lets through plenty of light When carefully installed, 8- or for good plant growth. However, 12-mil vinyl holds up for as long polyethylene constantly exposed as 5 years. to the sun deteriorates during Vinyl attracts dust and dirt the summer and must be replaced from the air and has to be each year. washed occasionally. Ultraviolet light energy causes polyethylene to break down. This TYPES OF FRAMES first deterioration occurs along (or over) the rafters and along Plastic greenhouse structures the creases where the film is range from crude wooden frame- folded. works to air-supported houses. Ultraviolet-inhibited polyethy- If you plan to build a plastic lene lasts longer than regular greenhouse, careful considera- polyethylene. It has an inhibitor tion should be given to economy that prevents the rapid break- of size and future expansion. down caused by ultraviolet light. Because plastic is available in UV-inhibited polyethylene is large widths and is lighter in available in 2- and 6-mil thick- weight, greenhouse rafters and nesses up to 40 feet wide and 100 supporting members can be feet long. widely spaced to permit maxi- Polyethylene permits passage mum light penetration. Common of much of the reradiated heat types of greenhouse frames are energy given off by the soil and as follows. plants inside the greenhouse. Therefore, a polyethylene green- A-Frame house loses heat more quickly In building an A-frame struc- than a glass greenhouse both ture, consideration must be given during sunny periods and after to the placement of cross rafters sunset. This is an advantage dur- (supporting members). Cross ing the day and a disadvantage rafters should be placed at least at night. one-third of the distance down

9 from the ridge on the outer raft- ers. Otherwise, it will be difficult to work around the cross rafters in applying an insulating layer of plastic. When the cross-rafter support is high in the peak of the green- house—especially in narrow greenhouses — an essentially clear-span type of structure per- mits easy application of an inner layer of plastic. The inner layer can be applied under the cross- rafter supports, leaving a small PN-2702 triangular air space in the peak An aluminum cold frame glazed with corru- gated fiberglass panels. Lightweight sash of the house. covers, lift or slide for ventilation control. Diagonal bracing wires provide (Photo courtesy of Lord & Burnham) added strength to an A-frame structure. This type of green- house is among the least difficult (a small plastic greenhouse used to build. for growing plants for later ). This structure requires accurate carpentry, and Rigid Frame construction costs are higher Rigid-frame structures have than for other frames because of been designed in widths up to 40 the added lumber and labor feet. This clear span structure needed to build the panels. has no columns to hold up the Advantages of panels are that roof section. they can be quickly installed and The best available rigid-frame taken down and stored during greenhouse has a 6-foot sidewall the summer; this will increase and is designed for 30, 36, or 40- the life of the plastic panels. foot widths. Panel greenhouses can be easily A prefabricated greenhouse ventilated. built with curved laminated wood rafters is commercially available. Quonset It has very low sidewalls (low Quonset greenhouses have the head room), and to grow tall same general shape as the quon- plants the structure must be set huts of World War II. Some raised higher on the foundation have been constructed of wood, sidewalls. but usually the frames are metal. The half-circle frames are cov- Panel Frame ered with one piece of wide plas- Panel-frame greenhouses are a tic and the houses are up to 20 modification of the sash house feet wide. The advantage of this

10 house is the ease of construction manure to insulate it from the and covering. Ventilation is by outside air and to retain heat. exhaust fans at the ends of the With a coldframe, you can do houses. many of the same things you do in a greenhouse. You can sow Pipe Frame summer fiowers and vegetables weeks before outdoor planting. A pipe structure can be used Often, you will gain sufficient to frame an air inflated green- time to grow an extra crop. You house. Air is introduced into a can start vegetables, annual chamber formed by two layers of flowers for fall and winter, and 4- or 6-mil film. perennials for next year's bloom. The effect of the air under Plants are protected from harsh slight pressure is to force the weather and will grow to trans- inner layer of film over the circu- plant size quickly. You can root lar greenhouse pipe frames. The cuttings of deciduous and ever- outer layer assumes a circular green shrubs and trees. Softwood shape over the frame and rides cuttings of chrysanthemums, on a cushion of air. geraniums, and fuchsia, and leaf The outer layer lifts 3 to 4 cuttings of rex begonias. African- inches from the frame at the top violets, and succulent and foliage and 1 to 2 inches from the frame plants take root faster in a cold- at the foundation sill. Air enters frame, particularly, during warm- the chamber through 6-inch plas- er months. tic tubing. You can also grow your own A manometer is used to meas- lettuce, chives, endives, parsley, ure static air pressure between and green onions right through the two layers of film. the winter by converting your coldframe to a hotbed. BEDS FOR GROWING Portable coldframes can be SMALL PLANTS built in your workshop from sur- plus materials you may have on Coldframes hand. A coldframe is a bottomless Coldframes are constructed box with a removable top. It is from sections of 3- by 4-foot or 8- used to protect small plants from by 6-foot millwork sash or plastic wind and low temperatures. No covered panels. Most coldframes artificial heat or manure is used can be converted to hotbeds for inside a coldframe. use in all seasons by installing Coldframes utilize the sun's electric heat, and automatic clock heat. The soil inside the box is controlled misting or watering. heated during the day and gives off its heat at night to keep the Hotbeds plants warm. The frame may be A hotbed is a bed of soil en- banked with straw or strawy closed in a glass or plastic frame.

11 It is heated by manure, electric- ity, steam or hot-water pipes. WEATHERPROOF WIRE Hotbeds are used for forcing Use weatherproof wire for all plants or for raising early seed- outside wiring. Wire size depends lings. Instead of relying on out- upon the distance to be covered side sources of supply for seed- and the number of hotbeds to a lings, you can grow vegetables circuit. Use approved terminal and flowers best suited to your equipment and follow safe wiring own . practices. All wiring must con- Seeds may be started in a form to local wiring codes. heated bed weeks or months be- fore they can be sown out of control temperature automati- doors. At the proper time the cally and make more efficient use hotbeds can be converted into a of electricity. coldframe for hardening. Then Because accurate temperature the plants may be moved to the control is possible with a thermo- garden when outdoor conditions stat, you can grow better plants are favorable. at lower costs by separating Between 10 and 15 watts of plants requiring different tem- electric heat should be provided peratures in different beds. for every square foot of growing Temperatures from 50 to 70 area in a hotbed. Soil-heating degrees Fahrenheit are best for tape or cable is available in sev- hotbeds. On very cold nights eral lengths, which give a choice cover the beds with mats, burlap, of wattages. straw, or boards. If the bed is in a sunny, well- sheltered location, and the cli- mate not too severe, 10 watts per HEATING square foot should be adequate. Many types of heaters and Lining the side walls with mois- heating systems are satisfactory tureproof insulation is desirable. for greenhouses. You must de- For localities with very cold cide which heating system best winters, a higher heat capacity is suits your greenhouse operation. needed. Fifteen watts per square Consider the initial cost, economy foot is recommended. of operation, and available fuel. Tape or wire screening, l^- or You can heat your greenhouse i/^-inch mesh, should be placed efficiently with coal, electricity, over the heating tape or cable to gas, and oil. prevent possible damage by cul- Heating equipment can be a tivating tools. space heater, a forced-air heater, Do not place hotbed cables of a hot-water or steam system, or any type directly in peat. When electric heaters. Radiant heat peat dries out it acts as an insu- lamps over plants and soil heat- lator and may cause the cable to ing cable under plants can also overheat. Use a thermostat to be used. 12 The capacity of your heating 0.8. If it is covered with only one system will depend on the size of layer, multiply by 1.2. This will your greenhouse, whether it is give you the required B.t.u. per covered with a single layer or a hour capacity of your heater. double layer of plastic or glass, In the example, a two-layer and the maximum difference be- greenhouse would be: tween inside and outside tem- 238,000 X 0.8=190,400 B.t.u.'s peratures. per hour. Heating systems are rated in The one-layer greenhouse British thermal units (B.t.u.'s) would be: 238,000x1.2=285,600 per hour. The firm from which B.t.u.'s per hour. you buy your greenhouse can tell The type of heating system you you what size of heater you will choose will depend on how much need; or you can estimate the you want to spend. The four size as follows: types are: • First, find the temperature • Space heaters. For low-cost difference. This is the difference heating for small greenhouses, in degrees Fahrenheit between use one or more ordinary space the lowest outside temperature heaters. WARNING: If you use and the temperature you want to a gas, oil, or coal heater, be sure maintain inside your greenhouse. to have a fresh air supply to For instance, if you want to avoid carbon monoxide buildup maintain a minimum inside tem- due to restricted oxygen supply. perature of 60° and the coldest Fans are also needed to improve night temperature you expect is circulation. Use high grade (low -10°, your temperature differ- sulfur) kerosene to avoid sulfur ence is 70°. dioxide damage; the need for • Next, find the number of high ignition temperature to square feet of exposed glass or avoid carbon monoxide and ethy- plastic in your greenhouse. Don't lene buildup is important. forget to add the areas of the • Forced-air heater. The best sides and ends to the area of the system for heating a small green- roof. house is a forced-air furnace with • Multiply the temperature a duct or plastic tube system to difference by the number of distribute heat. You can use a square feet. For example, suppose thermostat to control the tem- you have a 20 by 100 foot green- perature in the greenhouse. house with a total of 3,400 • Hot-water or steam heater. square feet of exposed plastic. A hot-water system with circu- You would multiply 3,400 by 70 lator or a steam system linked (the temperature difference). with automatic ventilation will This would give you 238,000. give adequate temperature con- • Now, if your greenhouse is trol. In some areas, coal or na- covered with two layers of plastic tural gas is readily available at or glass, multiply the 238,000 by low cost. This fuel is ideal for

13 hot-water or a central steam sys- equipment should be built into tem. Steam has an advantage in your greenhouse to control tem- that it can be used to sterilize peratures in all seasons. If you growing beds and potting soils. use hand-operated roof vents, • Electric heaters. Overhead they will require frequent tem- infrared heating equipment com- perature checks. As outdoor bined with soil cable heat pro- weather changes, sashes must be vides a localized plant environ- opened and closed manually to ment, which allows plants to keep plants from getting too hot thrive even though the surround- or cold. ing air is at a lower than normal Automatic ventilation elimi- temperature. Electric resistance- nates the manual work and is the type heaters are used as space best way to cool a greenhouse. heaters or in a forced air system. As an example, if your green- house has roof vents—a special electric motor and thermostat VENTILATION will open and close the vents. Even during cold weather a Fresh outside air is brought in greenhouse can get too warm on through the roof vents. Warm air bright, sunny days. So ventilation flows out through escape vents.

1071K318-4 An automatic heater and ventilator provide uniform plant environment.

14 Besides cooling the greenhouse Roll-up screens are available the change of air improves grow- with pulleys an* rot-resistant ing conditions. nylon ropes. These screens can Responding to this air trans- be easily adjustable from outside, fer, the thermostat will turn off as weather and sunlight vary. and on to keep temperatures Vinyl plastic shading is made right for plants. Fans provide of a flexible film that reduces good ventilation and are needed light from 55 to 65 percent. The in both large and small green- material comes in rolls and in- houses. stalls easily against the glass in- Exhaust fans should be large side your greenhouse. To apply, enough to change the air in the just wash the glass with a wet greenhouse once every minute. sponge, then smooth the plastic To accomplish this, the capacity onto the wet glass. When of the fan in cubic feet per min- smoothed into position it ad- ute at i/^-ii^ch static pressure heres to the glass. It can be should equal the volume of the pulled off and used again. greenhouse. The volume can be Shading compound can also be calculated by multiplying the applied on the outside of glass floor area by 7. greenhouses. It can be thinned If the greenhouse is high with paint solvents. It usually enough, place the exhaust fan comes in choices of white or and the motorized intake louvers green. Shading compound which above the doors at opposite end- mixes with water can also be walls. This will exhaust the hot- used. test, most humid air, and prevent a direct draft on the plants near EVAPORATIVE COOLING the intake. An evaporative cooler (or fan Fan and duct ventilation can and pad system) eliminates ex- also be used for automatic green- cessive heat and adds beneficial house heating and ventilation. humidity to the greenhouse at- Plastic ducts are suspended by mosphere. With an evaporative wires or straps from the roof of cooler, moist cool air is circulated the greenhouse. The fan-heater- throughout the greenhouse. louver unit gives positive air Warm air flows out through flow and the polyethylene duct roof vents or exhaust fans. Tem- distributes the incoming air even- perature is lowered, humidity is ly throughout the house. increased, and watering needs are reduced. SHADING YOUR You can select a cooler of the GREENHOUSE right size as follows: When protection from the sun • First, calculate the cubic is needed, use roll-up screens of feet of your greenhouse by multi- wood or aluminum, vinyl plastic plying the length by the width by shading, or paint-on materials. the average height.

15 • Next, add 50 percent to the total cubic space, then select a cooler which has at least this CFM (cubic feet per minute) air capacity rating. The cooler must be installed outside the greenhouse. If it is inside, it can only humidify and cannot cool. A properly sized cooler will reduce the greenhouse temperature approximately 80 percent of the difference between the outside wet-bulb and dry-bulb thermometer readings. In hot, dry areas this system can reduce the temperature from PN-2703 30 to 40 degrees. In wet, humid Fan and tube ventilation give positive air areas the cooling will be less. It is flow while the polyethylene ducts distribute the most effective during the hottest incoming air evenly throughout the greenhouse. The plastic ducts are suspended by wires or part of the day. straps from the roof of the greenhouse. (Photo courtesy of Edison Electric Institute)

MIST PROPAGATION CONTROLS choice of manual or automatic operations. Mist sprays are used in propa- gating to keep the atmosphere Evaporation System humid. There are two types of mist propagation controls. The This system provides a special most popular is by means of time unit that operates within the clocks. The other system controls mist spray from the nozzles. the cycles by evaporation from a When the stainless steel or cera- mechanical or electronic leaf or mic screen and the plants become screen. saturated, the screen tilts to a downward position, which switches off the water. Time Clock System The water evaporates both on This system of automatic wat- the mesh screen and on the cut- ering includes— tings. When the screen loses • A dual-time clock consisting weight, the screen raises and ac- of a 24-hour clock and a 6-minute tuates the switch. This opens clock, the solenoid valve and starts the • An electric water valve with misting cycle again, according to strainer. the needs of the cuttings. • Hose bibbs. Because this control is acti- • A toggle switch to give you a vated by the weight of the water.

16 it is fully automated and operates Closed greenhouses often have continuously day and night. too little carbon dioxide during the day to effectively utilize Watering Kits for Pot Plants available light. Therefore, plants grow poorly when air vents are Watering kits for pot plants closed. can also be used. Water is sup- By enriching the atmosphere plied directly to each plant with CO2, plant growth can be ac- through hollow plastic tubes, celerated. which are permanently attached. Because light and carbon di- One tube can be used for each oxide complement each other in small pot and two or more for plant growth, additional electric larger pots. Water tubes are lights in greenhouses combined weighted at the outlet end; each with good carbon dioxide control tube is approximately 5 feet long, will increase yields of lettuce, and can be cut to shorter length tomatoes, orchids, chrysanthe- if necessary. mums, carnations, snapdragons, geraniums, and other crops. CO^ AND LIGHT CONTROL CO2 equipment utilizing infra- Carbon dioxide (CO2) and light red sensors are available for are needed for plant growth. greenhouse owners who want to

PN-2704

A greenhouse can be part of the house, blending with the outdoor patio and enabling the gardener to live with plants the year around. (Photo courtesy of J. A. Nearing Co., Inc.) 17 benefit from carbon dioxide en- Plants differ in the need for richment with supplementary light; some thrive on sunshine, lighting. others grow best in the shade. The equipment will measure Most plants will grow in either and control CO2 levels from 0 to natural or artificial light. 2,000 parts per million which will Artificial light in greenhouses satisfy most of the production can be used in the following needs of greenhouse growers. ways: This equipment is fairly expen- • To provide high intensity sive and requires frequent cali- light when increased plant bration. growth is desired. Inexpensive color metric kits • To extend the hours of nat- are also available for determining ural daylight or to provide a the CO2 levels in your green- night interruption to maintain house. the plants on long-day conditions. Proper lighting not only ex- Forms of CO2 tends the gardening day by en- Forms of CO2 for enriching abling the gardener to work in greenhouse atmospheres follow: the greenhouse during the dark • Bottled CO2, which has been evenings of winter and early liquified from a burning process. spring, but it aids plant growth. This liquid CO2 is kept under Three basic types of lamps are pressure and is controlled by used in greenhouse lighting. means of a solenoid or metering They are— device. • Fluorescent lamps, which • Dry ice, which may be placed have the advantage of higher in a greenhouse or growth cham- light efficiency with low heat. ber in block form or placed in a This type of lamp is the most converter (a pressure bottle) and widely used for supplemental stored until needed. light. It is available in a variety • Burned sulfur-free gaseous of colors but cool-white lamps are fuels such as natural gas, L P the most commonly used. High gas, or a liquid carbon fuel such intensity (1500 ma) fluorescent as kerosene. tubes that require higher watt- age are also commonly used to reach 2000 foot candles. LIGHTINa TEMPERATURE. • Incandescent lamps, which AND CONTROL UNITS vary in size from 60 watts to 500 Plants respond to the relative watts. They are used to extend lengths of light and dark periods daylength in greenhouses. The as well as to the intensity and grower can vary f ootcandle levels quality of light. Artificial light by adjusting the spacing and has been used extensively to con- mounting height above the trol plant growth processes under plants. various conditions. • High-intensity discharge

18 (HID) lamps, which have a long provide that temperature. If you life (5000 hours or more). With want no more than frost protec- improvements made possible by tion, set the thermostat at 40° F. the addition of sodium and metal- Space heaters can maintain a halides the lamp has a high emis- minimum of 60° F. in the green- sion of light in the regions util- house. Higher temperatures on ized by plants. plant benches can be provided with soil-warming equipment. Light Meters Remember that heat is lost from a greenhouse by radiation, Inexpensive light meters are conduction, and convection available for measuring the light through— intensity in greenhouses. The • Glass. most common light meters are • Walls and other non-glass calibrated in foot candles or lux parts of the structure. (10.76 foot candles). • Floor or soil. • Ventilation, door openings, Temperature and cracks. As a gardener you will be con- cerned with two temperatures— Control Units the air temperature required in Automatic controls are im- the greenhouse and the minimum portant in greenhouses. Without outside temperature that your them switching lights, fans, heating equipment must over- come. For most plants, a night tem- BEFORE BUILDING YOUR perature of 60°-65° F. in the GREENHOUSE greenhouse is adequate. The gen- Almost every gardener even- eral rule, however, is not to have tually reaches a point where he a higher temperature than is wants a greenhouse. Before buy- necessary. ing or building one, you should— If you grow some plants that • Give careful thought to the require a higher temperature size, style, and kind of control than is provided in the green- desired. house, use a propagating case or • Contact your county agricul- a warmed bench with thermo- tural agent so he can help you statically controlled warming locate and visit a few of your cables to warm the air surround- neighbors who have garden ing the plants. This can be done greenhouses. Learn about their at a fraction of the cost that problems so that you can choose would be necessary to heat the the best greenhouse for you. whole greenhouse to provide the • Check local building codes same temperature. and zoning laws before you start If you want a temperature of construction. 60° F., install heaters that will

19 pumps, heaters, and misters on Edison Electric Institute, Electric Gardening, Edison Electric Institute, and off at a prescribed time 90 Park Avenue, New York, 1970. would be a complicated and la- (Available from your local electric borious task. power supplier.) Many time clocks, photocells, Liu, R. C, Bailey, W. A., Klueter, thermostats, and other controls H. H., and Krizek, D. T. New Shapes of Hobby Greenhouses, U.S. Depart- are available commercially. When ment of Agriculture, ASAE Paper 68- used individually or in combina- 925. Phyto-Engineering Laboratory, tion they will provide any time Beltsville, Md. 20705, 1968. interval or control desired. Lord and Burnham, Your Gateway to Year-round Gardening Pleasure, Burn- ham Corporation, Irvington, N.Y., 1971 For further reference : (Free). Lord and Burnham, Greenhouse Acme Engineering and Manufactur- that Take Care of Them- Corp., The Greenhouse Climate Con- selves, Burnham Corporation, Irving- trol Handbook: Principles and Design ton, N.Y., 1971 (Free). Procedures, Acme Engineering and Potter, Charles H., Greenhouse: Manufacturing Corp., Muskogee, Okla., Place of Magic, E. P. Dutton and Co., 1970. $2.00. Inc., New York, 1967. Biles, Roy E., The Complete Book of Sunset Book, Garden and Patio Garden Magic, J. G. Ferguson Pub- Building Book, Lane Magazine and lisher, Chicago, 1953. Book Co., Menlo Park, Calif., 1971. Blake, Claire L., Greenhouse Gar- $1.95. dening for Fun, M. Barrow and Com- Sunset Book, Garden Work Centers. pany, Inc., New York, 1967. Lane Magazine and Book Co., Menlo Coutier, J. W., and Curtis J. 0., A Park, Calif., 1970. $1.95. Simple Rigid Frams Greenhouse for U.S. Department of Agriculture, Home Gardeners. Cooperative Exten- Electric Heating of Hotbeds, Leaflet sion Service, Circular 880, University 445, V^ashington, D.C. 20250, 1969. of Illinois, College of Agriculture, Ur- U.S. Department of Agriculture, bana 1964. Out of State, 10(i. Plastic Covered Greenhouse Coldframe, Coutier, J. W., and Curtis, J. O., Miscellaneous Publication 1111, Wash- Home Greenhouses for Year-round ington, D.C. 20250, 1969. Gardening Pleasure, Cooperative Ex- U.S. Department of Agriculture, tension Service, Circular 879, Univer- List of Sources of Information on sity of Illinois, College of Agriculture, Greenhouses, Correspondence Aid 34- Urbana, 1964. Out of State, 10^. 134, Washington, D.C. 20250, 1970.

Information for this publication was furnished by Wil- liam A. Bailey, Robert C. Liu, and Herschel H. Klueter, agricultural engineers, Northeastern Region, Agricultural Research Service.

Issued March 1973 WASHINGTON, D.C. Slightly revised January 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 25 cents domestic postpaid, or 15 cents GPO Bookstore Stock Number 0100-02661

lîr U.S. GOVERNMENT PRINTING OFFICE : 1975—0-566-188