Research Report No. 5
By Norman L. Marshall
March 1987
This work was partially funded by the Jessie Smith Noyes Foundation
Copyright 1987 by The New Alchemy Institute. All rights reserved. Printed in the United States of America. Except for brief quotations used in critical articles or reviews, no part of this publication may be reproduced or transmitted in any form by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the copyright owner. For information, write to The Green Center, 28 Common Way, Hatchville, MA 02536 USA.
Reprinted November 1990.
ISSN 0898-686X
ISBN 0-933822-07-3
CONTENTS
Light levels
Growing temperatures
Ventilation and summer cooling
Cost
Crops
Growing medium
Renewing of growing medium
Pest control
Space for plants
Labor versus labor-saving capital
Seasonal versus year-round operation
Issues of scale
Financing
Markets and marketing
Land cost
Risk
Greenhouse as Part of an Integrated Farm
Seedlings/Market gardening
Composting greenhouse
Fish farming
Other animals
Increased food production in greenhouses in the Northeastern United States has been proposed as a way of decreasing dependence on imported food sources, a way of employing people, and a way of raising fresher, more healthful food. Much of this interest has come from individuals and groups promoting a more ecological approach to food production. Because of this interest, two separate literatures have developed--a conventional greenhouse literature, and an ecological greenhouse literature. In many cases, information in the ecological greenhouse literature is difficult to apply to commercial greenhouse systems. If ecological greenhouse research is going to be picked up by commercial operators it must be carried out within a context of complete, commercial systems. A profitable food-producing greenhouse business is possible in the Northeast, but success is difficult to achieve and requires good physical design, good horticultural design, good operation, and careful attention to business details. As in the rest of agriculture, the trend is towards more part-time operations and large-scale corporate operations, and towards fewer full-time, family operations. In any greenhouse research program, the full-time, family-scale operation will be the most difficult audience to serve because they can not afford to experiment.
Increased food production in greenhouses in the Northeastern United States has been proposed as a way of decreasing dependence on imported food sources, a way of employing people and away of raising fresher, more healthful food. Much of this interest has come from individuals and groups promoting a more ecological approach to food production (low energy use and low use of agricultural chemicals, especially pesticides). Nevertheless there has been little increase in commercial food production in greenhouses in the Northeastern United States,ecological or otherwise. Most glasshouse vegetable growers were put out of business by the increases in fossil fuel prices in 1973-4 (Lucie 1984). New hydroponics vegetable growers have had a rocky beginning. Massachusetts has 14 hydroponics growers with a combined total of about 2 acres of greenhouse, but only 2 of the 14 growers are doing well enough to be operating at full capacity (Miller 1984). There is very little greenhouse space in the Northeast devoted to commercial ecological greenhouse food production.
Below I devote a section to each of these topics. For each topic I review current conventional greenhouse practice, review alternative ecological greenhouse ideas, and suggest which of the ecological ideas offer substantial promise.
Conventional greenhouses and ecological greenhouses have differed in their emphasis when making tradeoffs between the primary physical design goals of high light levels, good growing temperatures, low energy use, and low cost. Conventional greenhouse design has tended to emphasize high light levels, good growing temperatures, and low cost. In solar greenhouse design, these factors have been considered, but the primary test of success has been that no auxiliary heating fuel be required to maintain a certain minimum temperature.
In comparing solar greenhouse designs and conventional designs, Albright emphasizes that for commercial growers the quantity, quality, and timing of their crop is more critical than the fuel bill (Albright 1981). Timing is most important in floriculture, where much of a year's income may depend on having the crop ready for specific holidays such as Christmas, Easter, or Mother's Day. Timing is critical for vegetable crops as well, as the highest prices will be received in particular seasons. In addition, the longer the crop occupies space, the higher the labor and overhead costs.
Commercial growers require as much natural light as they can get in order to produce their crops in the shortest time possible. They maximize greenhouse surface (up to about 80-90 percent of the total), use highly light-transmissive glazing, and minimize shading from glazing support (generally through the use of a lightweight metal frame). Commercial growers are wary of the ecological greenhouse idea of a substantial north-facing opaque wall because of the loss of indirect light in cloudy weather. Cerilli (1979) found that a Brace Institute-style solar greenhouse showed a significant decline in both the quantity and quality of winter potted chrysanthemums compared to a conventional glasshouse when both were heated to the same temperature. A computer simulation shows that in Massachusetts, more than 10-20 percent reflective, opaque insulation on the North results in a net loss of light to the growing area (Wolfe 1982). Supplemental lighting is used extensively for seedling production, but is generally too expensive for main crop production.
Temperature, especially soil temperature, is another key to plant growth and timing. Conventional greenhouse owners typically use a standard temperature profile - one temperature for daytime and another for night. When growers turned down their thermostats in response to the fuel crisis in 1973, the crop was delayed and,paradoxically, more energy was used over the life cycle of the crop because of the longer production time (White 1983). Solar greenhouse operators have avoided use of supplemental heating, and have generally sacrificed growth. Optimal temperature ranges for growth are generally much more limited than those required simply for survival. Lettuce is a crop that can survive very low night-time temperatures but Schippers has found that higher night-time temperatures helps growth and helps control fungus. He has tried lower night-time temperatures, but now uses 60 degrees F (Schippers 1984).
Conventional greenhouse operators have introduced a number of heat-conserving features. The old greenhouse standard had been one layer of glass; the new standard is two layers of 6 mil polyethylene (Brennan 1983). This new standard is being improved upon by new glazings such as Monsanto's Cloud 9R that are more infrared-reflective than normal polyethylene. Movable night insulation can be highly effective in energy conservation. The insulation can be as simple as a thin, semi-transparent sheet of woven polyester fabric that can double as shading material, or as elaborate as a sandwich material with a high R-value. White calculates that while the best thermal blanket would save 40 percent of annual heating costs for a single-glazed glasshouse in Pennsylvania, a summer-shade material will save about 25 percent on heating costs and also save 50 percent on summer ventilation costs (White 1983). Because this material is very inexpensive, this can be the most cost effective route in movable insulation. A second approach to movable insulation is blowing polystyrene beads between layers of glazing at night. This approach can save up to 90 percent in heat (Bauerle 1984). A third approach to inexpensive movable insulation is to use inflatable polyethylene tubes as is being done in the Skillins Greenhouses in Maine (Donovan 1984). After double-glazing, adding movable insulation is probably the next most cost-effective energy-conserving measure for most greenhouses.
Another method of energy conservation in greenhouse heating is to improve the efficiency of heating the the plants. The most promising technique, and one that is beginning to be adopted widely, is "root-zone heating." In applying the heat directly to the soil the plants are kept warm even with lower air temperatures. With lower air temperatures there is less heat loss. These systems cost an additional $.75-$1.00 per square foot including the cost of a porous concrete floor but have saved up to two thirds of heating costs in some cases (Roberts 1984).
Alternative fuels can be used to heat greenhouses. Several greenhouse operators outside Allentown, Pennsylvania use waste heat from coal-fired electrical generating plants to heat their greenhouses. They pay the utility for the heat, but the payments are far less than if they were burning the coal themselves (Salitan 1984). Heating greenhouses with compost and with animal heat will be discussed in the section on the greenhouse as part of an integrated farm (page 11).
A final widespread and very important method of saving heat energy in midwinter is shutting down part or all of the greenhouse.
Ecological greenhouse designs have tried the above strategies plus the use of insulated, opaque structure on the north, three or more layers of glazing, the use of thermal mass, the use of an active solar heating system, and the use of insulating gases between layers of glazing. The use of insulated opaque structure can be quite damaging to winter light levels as noted above. Albright also notes that the strategy is impractical for commercial-scale greenhouses as they are too wide for an A-frame type design to be feasible (Albright 1981). Such structural walls add a great deal of cost to a greenhouse structure (Wolfe 1982). Multiple layers of glazing cuts light levels and adds to structural cost, requiring that the tradeoffs be carefully weighed.
Passive thermal mass systems have major drawbacks in conventional greenhouses. Cornell's Albright (1981) writes:
Commercial production follows a blueprint plan of night and day temperatures to achieve timing of the crop. Timing is especially critical for holiday crops. The blueprint temperatures are a constant night temperature, and a constant but higher day temperature. Quick transitions from one temperature to the other is assumed and usually realized in typical greenhouses. A large thermal mass acts to retard quick temperature changes; thus it acts against the programmed temperature control. In the morning when the greenhouse is at its lowest temperature, and the outside air is also, having to heat an extra, large thermal mass places a double burden on the heating system. Also, much of the heat added to the extra thermal mass actually comes from the early morning operation of the furnace, not the midday sun. Then at night the extra thermal mass can help keep the greenhouse above the prescribed night temperature, except during cold nights, and accelerate maturing of the crop. Venting to reach the night temperature more quickly wastes heat added by the furnace. Thus, although some augmentation of the thermal mass may be desirable, it must be done with care to avoid creating problems.
The thermal mass system will be particularly ineffective if there are times when there isn't surplus heat during the day. Other reasons why thermal mass systems haven't been adopted by commercial operators are that they occupy valuable growing space and absorb light. In larger greenhouses, mass along the north wall would be far from the southern part of the greenhouse (Albright 1981). Active designs that move heat only when desired have been tried. Designs range from large stand-alone solar collectors of the same size as the greenhouse (Milburn et al. 1977) to small bags of water that can be filled and emptied next to the plants (Albright 1981). The expense and complexity of these systems has so far prevented their widespread adoption.
An alternative to heat storage is preventing heat losses. New Alchemy has experimented with the use of gases other than air (argon, in the case of the Pillow Dome) between layers of glazing for lower heat losses (Seale 1983). This is an idea that has promise, but is unproven in a commercial setting.
As is discussed in the section on pest control (page 8), fungus problems are greenhouse operators' most difficult pest problems. Conventional greenhouse operators use great amounts of ventilation in concert with chemical fungicides. Solar greenhouse operators have often used no fungicides out of ecological concerns, and have used less ventilation also. Less ventilation than optimal has been used to save electricity, to hold heat, and/or out of ignorance. Schippers has found that forced ventilation to remove humidity is critical to the health of his lettuce, even in midwinter (Schippers 1984) The humidity problems can be lessened through subsurface watering systems. (Boice 1984). Heat exchangers can be used to conserve some of the heat that would be otherwise lost in the exhaust air (Hanson et al. 1983). Whatever the approach taken, any commercial food-producing greenhouse must manage its humidity.
Forced ventilation is also used widely for summer cooling in conventional greenhouses to keep temperatures at optimal levels. Forced ventilation rates in Maine for greenhouses can reach one air exchange per minute (Gilman 1984). Another approach used for cooling is shading - either a whitewash covering on the exterior of the greenhouse or fabric curtains inside. Solar greenhouses have more typically relied on passive cooling systems. These systems include the use of thermal mass and better-designed natural ventilation systems. These systems are somewhat effective, but summer temperatures in most solar greenhouses exceed optimal temperatures by a fair margin. Ventilation can be costly. Schippers (1984) estimates that ventilation (electricity) costs him half of what heating (coal) does annually.
Conventional greenhouse structures cost very little - often less than $1 per square foot for framing and glazing in a form that can be erected very easily. However, the framing and glazing is only a part of the total investment required. Other expensive items in a conventional greenhouse investment include: construction labor, heaters, fans and shutters, flooring, and a horticultural bed system. For Schippers' simple hydroponic systems the materials for the frame and glazing of a 4930 square foot greenhouse have a total cost of $4200 or a little less than $1 per square foot. The total investment is $22,000 or about $4.50 per square foot (Lichtman 1984).
Solar greenhouses have typically cost much more, although it is often hard to get accurate data because of donated labor and/or materials. Custom wood-framed greenhouse structures have cost up to $40-50 per square foot or even more. The materials cost alone for a typical wood-framed A-frame type solar greenhouse can be more than the cost of an entire, installed conventional greenhouse system. A more cost-effective approach to building energy-conserving greenhouse systems would be to buy as many components as possible off the shelf and to avoid totally custom systems. New Alchemy has taken this approach in its most recent greenhouse design, the composting greenhouse prototype. This small greenhouse uses a commercial greenhouse frame and glazing. Cost of this system was about $10 per square foot (Lichtman 1984).
Many new greenhouses, particularly solar greenhouses, have been planned with a disproportionate amount of attention to the physical design. Not enough attention has been paid to the horticultural design. What crops will be grown? How will they be grown? What growing medium will be used? How will pests be controlled?
As noted in the introduction, I focus here on food crops. Other crops,especially flowers and other ornamentals, generally give higher revenues per square foot of greenhouse. (They can also have higher costs associated with them as well.)
In growing food in greenhouses in the Northeastern United States,there are three possible general strategies. These are: to try to grow high-revenue specialty crops; to grow large quantities of basic vegetables such as tomatoes and lettuce at a low cost; or to grow significant quantities of basic vegetables, but to differentiate the product as higher quality, and thereby receive a higher price.
The first approach, growing high-revenue specialty crops, is likely to be the only one of the three strategies that could return high rates of profit. It is also an approach that is risky and short-term in nature. Specialty crops are luxury crops, and tastes may change quickly. Even if demand holds,unless the market niche is very small, a successful business will attract competitors and prices will drop.
The second approach is to intentionally produce a "commodity." A commodity is a product where there are many suppliers (growers)and the market (the customer) doesn't see much difference between suppliers. Therefore the customer will select the product with the lowest cost. The suppliers (growers) who will survive in this sort of classic "free" (cut-throat) market will be the ones with the lowest production costs. Larger operators have inherent advantages in this sort of market. Small growers do have a chance in some cases. Schippers ships hydroponics lettuce 52 weeks a year and markets most of it through one of greater Boston's largest supermarket chains. He competes somewhat on quality, but largely on price at a wholesale price of $.37 1/2 per head (Schippers 1984). Lettuce is the only crop where greenhouse growers have been able to compete on price in New England. The other most common vegetable grown, tomatoes, has fallen into disfavor among growers because they have lost money with it (Finney 1984). European cucumbers grow well in greenhouses but haven't yet found a steady market (Schippers 1984).
Even the lowest cost suppliers in a commodity business will seldom make great amounts of money. The only way to receive higher prices is through "product differentiation." For greenhouse food production in the Northeastern United States,there are several grounds around which to differentiate the products produced. First the product is "local" or "native. "These terms can often receive a higher price, especially if the produce really is fresher, better tasting, and more nutritious. Another area that has been exploited with locally grown produce is in the area of "organic" produce. If greenhouse produce were grown either totally organically, or were at least free of pesticides, a higher price could be obtained. Receiving the higher price may require extra advertising, or special marketing techniques, but product differentiation is probably the best route for the small greenhouse producer.
What are possible revenues for a food-growing greenhouse in the Northeast? Schippers raises 85,000 heads of lettuce per year in a 4930 square foot greenhouse. At a wholesale price of $.37 1/2 per head the sale of his produce generates revenues of $6.46 per square foot of greenhouse. This is consistent with possible revenues for ecological cropping patterns. New Alchemy yields are typically about 3.5 pounds per square foot for spring tomatoes and about two pounds per square foot for fall tomatoes (Armstrong 1984). If the average price is $1.00 per pound (wholesale, out-of-season, ecologically-produced tomatoes), these crops alone will yield $5.50 per square foot of growing space or perhaps $4.40 per square foot of greenhouse. Five to six dollars per square foot of greenhouse per year is a realistic goal for revenues.
Soil is the traditional growing medium, but many industry observers predict that the use of soilless media and hydroponics will continue to expand (Bauerle 1984). Advantages of soilless media can include: predictable uniformity; flexibility (can make adjustments for weather by changing liquid mix and the larger buffering capacity provides a greater margin for error in fertilizer application); light weight; greater water-holding capacity; availability; and freedom from disease and weed seeds (Scholes 1984).
In addition to the advantages listed above, growers such as Dr. Pieter Schippers of Ashby, MA, have used soilless media in conjunction with the "nutrient film" hydroponics system in whole systems that provide significant cost savings. In Schippers' system, a key is that lettuce transplants can be started in narrow gutters that are very close together. As the lettuces grow, the gutters can be spread out. This method allows Schippers to harvest about 20 lettuces per square feet of greenhouse per year (Lichtman 1984). In this way Schippers may be growing up to twice as many lettuces as he could with the same amount of space if the lettuce required its maximum amount of space throughout the entire growth period. Saving space does not only save greenhouse cost, but also saves in heating and ventilation costs. With low margins in a commodity business, that is more than enough of a difference to be the difference between economic success and failure. (For more information on optimal use of space in greenhouses, see the section on space for plants, page 8).
Virtually all commercial greenhouse growers use chemical fertilizers to replenish nutrients taken up by the plants. The nutrient film hydroponics technique represents the extreme in this approach. The plants are grown in a sterile, practically nutrient-free media, and all nutrients are provided by a constant bath of nutrients in solution.
Organic methods for the greenhouse require bringing in large quantities of organic matter from outside greenhouse. In greenhouse cost discussions, fertilizer costs are generally lumped with other material costs and then total to one of the minor cost items. For example, pesticide and fertilizer costs totalled about 1 percent of all costs for greenhouse floriculture crops in New York in 1981 (Stathacos & White 1981). Therefore, organic fertilizers can not be expected to lower costs. However, a totally organic approach could result in organic produce that could command a higher price in the marketplace.
Commercial greenhouse growers have relied heavily on chemical insecticides and fungicides in producing large crops with good appearance. Interest in using I.P.M. (integrated pest management) in greenhouses is increasing. Only a few greenhouse insects are consistent pests. Biological control programs have been developed for these pests, and the beneficial insects required are becoming increasingly available commercially. Fungus problems are more difficult to correct than insect problems (Armstrong 1984). At least one big greenhouse grower in Ontario uses no insecticides, but still uses one fungal spray in the spring (Gilkeson 1984). Ventilation is the key to prevention of fungal problems. Humidity must be kept to 50-60 percent, especially in the early morning (Gilkeson 1984).
Like fertilizers, pesticide costs are normally a minor cost for intensive, greenhouse agriculture. Biological pest control in Canada costs about $.30 per square feet the first year (Gilkeson 1984). A factor encouraging adoption of biological controls is a concern about whether the pesticides that the growers need will be available in the future, due to increasing regulation. As with organic fertilizers, a possible benefit of not using chemical pesticides is to be able to sell the produce as "organic" at a higher price.
Robert Aldrich of the University of Connecticut outlines some general rules for efficient operation. Optimal greenhouse layout and operation is very much like that in a factory. Flow of materials and products should be designed so that the flow is all in one direction. Materials should flow to the worker instead of the worker going to the materials. Retail areas and their traffic flows should be separated from growing areas.
Schippers' system for maximizing lettuce production in a hydroponics growing system was discussed in the section on growing medium (page 7). Dramatic gains in space utilization over conventional practice can be achieved in soil systems as well. Much of the gain can be achieved simply through a better layout, according to Bartok (1984). A traditional greenhouse with wide aisles lengthwise in the greenhouse has plants occupying only 50-60 percent of the space. Using a wide aisle up the center with narrow peninsulas down the side can give another 10-15 percent in space utilization. By using movable benches, so that workspace is created only when and where needed, space utilization of up to 90 percent can be achieved. This sort of system adds $2-4 to the total greenhouse cost, but that cost can be justified when compared to the cost of the structure and heat, or to the lost revenues. Maximizing growing area within a greenhouse is one of the easiest ways to make the greenhouse and heat dollar go further.
Along with the cost of the greenhouse structure, the cost of labor will be the greenhouse operator's highest cost. This is true whether the labor is paid or represents the owner's return on his own labor. As discussed in the section on crops (page 6), one should not plan on annual revenues per square foot of growing space of greater than $5 per year for food crops in the Northeast. Therefore, we may place an upper bound on the cost we can afford to pay for labor of about $2 per square foot per year. This is not much. Schippers spends about 8 cents per head of lettuce which works out to a total cost of about $1.60 per square feet per year for labor. This is at labor rates of $2.75-$4.00 per hour for neighborhood youth and other part-time employees.
Schippers operates an efficient, family-style, labor-intensive operation. If one were to try for lower overall labor charges,or had to pay more per labor hour, one would be required to mechanize. This is becoming the norm for larger greenhouse operations. Some of the mechanizations being widely adopted include automatic watering and feeding systems, microprocessor climate control, soil-mixing machines, and monorail or conveyer belt materials-handling systems. John White of Penn State said in 1982: "Today it takes one skilled and two unskilled workers to run an acre of greenhouse. "Within five years the same three people will be able to run 10 acres of greenhouse, but all three will have to be skilled."
A food-producing greenhouse operator should consider carefully whether year-round operation is optimal. Schippers grows lettuce 52 weeks a year. He grows smaller lettuces in the winter when light levels are lower, but the market is best. He grows larger lettuces in the summer when the growth is fastest, but the market is weakest. He sells the lettuce for the same price year-round. His winter lettuce helps sell the summer lettuce.
Other crops such as tomatoes and European cucumbers are grown as either spring crops or fall crops. If the greenhouse is kept open, lettuce or Chinese greens are typically grown in the winter months. Without the year-round market, the greenhouse could alternatively shut down for the winter months. There would be savings in energy cost, and could also be savings in the cost of energy-conserving greenhouse features. Since light levels are low, growth and revenues given up would be relatively small. It is also important to consider whether hiring seasonal labor is feasible.
In addition to a good physical design, good horticultural design,and good operation, a successful greenhouse venture requires good business planning. Issues of scale, markets and marketing, financing, land cost, and risk are important considerations.
Mechanization is required for a labor-efficient operation. Specialization is a result because an operator can afford to mechanize in only a few areas. With mechanization and specialization comes larger scale. A single person or small group can produce more, and will need to produce more in order to pay for the labor-saving tools and machines. The advantages of larger scale are: the ability to spread fixed costs; volume sufficient to justify mechanization; more skilled workers (specialized rather than diversified); lower input prices; and possibly higher product prices (Schertz 1979).
All of these economies of scale are present in greenhouse operations. If current trends continue we will see larger and larger greenhouse businesses. At current prices I estimated in the section on seasonal versus year-round operation (page 9) that $2 per square foot per year of growing space could be spent for labor. If the greenhouse business is to provide a livelihood for a family, a 10,000 square foot size is about the smallest scale that can be recommended for food-producing greenhouses in the Northeast.
Along with labor, the cost of the greenhouse and equipment will be the highest cost item for a greenhouse business. The precise annual cost of the greenhouse will depend on the business climate, inflation, the lifetime of the components, tax considerations, and so forth. A detailed analysis should be done before starting any new business. For the purposes of this paper let us just say that if we financed conventionally, we might have to pay 20 percent of the total investment or more per year, but with government development support (low-interest loans, tax breaks, investment tax credits) and with interested investors we might have to pay only 10-13 percent of our total investment per year. If we could allocate $2 per square foot per year (as we did with labor) we could invest a total of $10-20 per square feet of structure. This total investment includes the cost of the land, improvements to the land such as driveways and utility hookups, and horticultural, watering, and other systems.
Before starting any new business, it is critical to develop a conscious market strategy and to do market testing. Different marketing strategies are discussed in the section on crops (page 6).
In a fully-developed greenhouse complex, the cost of land will probably not be the most important determinant of success or failure. Even if land costs $25,000 per acre, the cost of the greenhouses and equipment is likely to be considerably higher. For example, if the land is half covered with greenhouse at a cost of $10 per square foot the greenhouse cost will be over $200,000 for a 1-acre lot. Land cost may be a significant issue if extra land is purchased for expansion, or if other agricultural ventures are planned for the same site. Otherwise, proximity to good markets will generally be more important than land cost.
Food-growing greenhouses in the Northeastern U.S. are a capital-intensive investment offering at best rather modest returns. For a business to be successful, it must succeed in several different areas as has been discussed above. A failure in any one of these areas could be an overall failure. The majority of new hydroponics growers in Massachusetts are struggling due to inexperience and general mismanagement.(Miller 1984). Food production in greenhouses in the Northeast is a risky business. It is not surprising that a business requiring a large investment, having relatively low returns, and having substantial risk would be growing slowly. Let the entrepreneur beware!
The biggest obstacle in any integrated farm venture is the need to be of appropriate scale in each area for low cost and for mastery of the business. Although the integration between a greenhouse and other farm enterprises likely will have some economic benefit, this benefit will be unlikely to be great enough to dramatically change the scale of the greenhouse required. Therefore the size required for a successful integrated farm could be even larger than that required for a successful specialized greenhouse enterprise.
Many market gardeners have small greenhouses that they use to grow seedlings for their own plantings, and to sell to their vegetable customers. As these greenhouses often are used for only a couple months a year in the spring, they are typically inexpensive structures that are relatively energy inefficient. They could be used for vegetable production if off-season labor could be used effectively in the greenhouse. However, the match isn't that good. The market gardener can not use off-season labor and sell year-round as Schippers does. If the market gardener grows a spring crop such as tomatoes, the busy harvesting period would be late spring-early summer. This is one of the market gardener's busiest seasons. A fall crop might work better if the planting could be worked into late summer harvesting and marketing, but the fall crop is of lower value and won't produce enough revenues to pay for greenhouse expansion. The market gardener's small greenhouse (perfectly adequate for seedlings) could be too small to be worth the trouble of planting.
In the composting greenhouse prototype being tested at the New Alchemy Institute, compost provides valuable heat and carbon dioxide to the plants (Fulford 1983). Fulford and I analyzed the economic benefits of integration for a composting greenhouse, assuming that each of the separate businesses (greenhouse and composting) make sense commercially on the site chosen (Fulford and Marshall 1984). For New Alchemy's prototype composting greenhouse, 48 by 12 feet for 576 square feet with a 12 cubic yard composting chamber, the economic value of the benefits was estimated to be as much as $1700 per year with optimal operation of both businesses. There are potential disadvantages of integration as well. If the composting process and the greenhouse are fully connected without any controls, problems could develop from too much heat, or nitrogen, or carbon dioxide, or water. Alternatively we might manage these problems but only through additional knowledge and/or labor or through additional monitoring and control equipment, an additional expense. Other potential disadvantages (separate from those arising from co-siting) or an integrated composting greenhouse include: the requirement for enclosed composting with forced aeration (relatively expensive in investment cost), and the need for some additional mechanical energy (generally this means more electricity) to push the air through filters in entering the greenhouse. (For more information on composting greenhouses see other New Alchemy Institute Research Reports.)
Another idea that has been advanced and developed at the New Alchemy Institute is integrating aquaculture into greenhouses (Zweig 1908). This is an intriguing idea - the aquaculture tanks serve as thermal mass heat storage for the greenhouse, fertile water can be used for fertilizing and watering the plants either conventionally or in a hydroponics system, and the filtered water can be returned to the tank. These ideas are unproven in commercial settings.
Small animals (in this case chickens and angora rabbits) have been included as a heat source in Anna Edey's Solviva greenhouse on Martha's Vineyard (Edey 1984) There are some technical issues concerning ammonia, but the primary problem with this scheme is that the animal business needs to be roughly of commercial scale. For the egg business, a successful operator with only 2500 hens is considered a rarity these days (Goldman 1984). With even a few hundred hens, an integrated egg-greenhouse business is likely to lose more money on the eggs than it makes through the integration, unless a very high price is received for the eggs.
I draw several important lessons from this literature review:
1. There are two separate literatures - a conventional greenhouse literature, and a ecological greenhouse literature. In many cases information in the ecological greenhouse literature is difficult to apply to commercial greenhouse systems.
2. A profitable food-producing greenhouse business is possible in the Northeast, but success is difficult to achieve and requires good physical design, good horticultural design, good operation, and careful attention to business considerations. It is unlikely that the benefits from integration with other businesses will compensate for failures in any of these areas.
3. There are three distinct classes of commercial food-producing greenhouse operators: part-time operators (less than 10,000 square feet of greenhouse); full-time family-scale operators that rely on the business as a sole source of income (10,000-40,000 square feet); and corporate-scale mechanized systems (40,000 square feet and up). Current trends are (as in the rest of agriculture) towards fewer family-scale operators and more corporate-scale and part-time operators.
4. Each of the groups has different research needs. Traditional agricultural research probably benefits corporate-scale operators the most. Ecological greenhouse research has helped the part-time operator some, but not as much as it could have helped if the research had been carried out more within a context of complete, commercial systems. The family-scale operator (and potential family-scale operators, as there are now few actual operators) has been helped the least. This operator is the hardest to help because they can not afford to experiment. They need proven, commercial food-producing systems.
Albright, L. D. 1981. "Heating Commercial Greenhouses Passively with Solar Energy." Presented at the 1981 Summer Meeting of the American Society of Agricultural Engineers, Orlando, FL.
Armstrong, C. 1984. New Alchemy Institute. Personal communication.
Bartok, J. 1984. "Increase Space Utilization with Moving Benches." Presented at the New England Greenhouse Conference. Sturbridge, MA: October, 1984.
Bauerle, W. L. 1984. "Ohio Agricultural Research and Development Center." Quoted in Avant Gardener, Vol. 16, No. 12, October 1984, p. 93.
Boice, W. 1984. "Labor Saving Watering Systems." Presented at the New England Greenhouse Conference. Sturbridge, MA: October 1984.
Brennan, T. 1983. "Retrofit of a Commercial Greenhouse with High Transmittance Film." In Energy Conserving Solar Heated Greenhouses: Horticulture and Technology Working Together. New York, NY: American Solar Energy Society, Inc., 1983.
Cerilli, R. V. 1979. "The Effect of Energy Conservation and Alternate Energy Techniques on the Production of Two Commercial Floriculture Crops." Thesis, Cornell Univ. Libraries, Ithaca, NY. Reported in Albright, p. 3.
Donovan, C. 1984. "Skillins Greenhouses: Commercial Growers Go Solar In Maine." In Northeast Sun, April, p. 11-12.
Edey, A. 1984. Solviva. West Tisbury, MA. Personal communication.
Finney, E. 1984. Cape Cod Hydroponics, quoted in Damkoehler, D. J. "The Good Earth Has Nothing Whatever To Do With Ed Finney's Lettuce." In Cape Cod Business Journal, November, 1984.
Fulford, B. 1983. "The Composting Greenhouse." In New Alchemy Quarterly, #14, Winter, 1983.
Fulford, B. and N. Marshall. 1984. "The Economics of Integration: The Composting Greenhouse as a Case Study." In New Alchemy Quarterly, #18, Winter 1984.
Gilkeson, L. 1984. MacDonald College. Ste. Anne de Bellevue, Quebec. Personal communication.
Gilman, F. 1984. "Cooling Your Greenhouse." Presented at the New England Greenhouse Conference. Sturbridge, MA: October 1984.
Goldman, W. 1984. "A Small Flock." In New England Farm Bulletin, #204, p. 1, 7-8.
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An Economic Comparison of Four 10,000-Square-Foot,
Food-Producing Greenhouses for Cape Cod, Massachusetts
Norman Marshall (1986) 19 pages
An Analysis of Costs and Returns in Conventional
and Organic Vegetable Production
Kurt Teichert (1986) 15 pages
The Composting Greenhouse at New Alchemy Institute:
A Report on Two Years of Operation and Monitoring
Bruce Fulford (1986) 24 pages
Report on a Survey of New England Organic Farms
Kurt Teichert and Debra Schulz (1987) 23 pages
Laboratory and Field Application of Entomogenous Nematodes
for Control of Insect Pest Species: Literature Review 1986
Dave Simser (1988) 21 pages
Laboratory and Field Application of Entomogenous Nematodes
for Control of Insect Pest Species: Laboratory and Field Trials 1986
Dave Simser (1989) 20 pages
Laboratory and Field Application of Entomogenous Nematodes
for Control of Insect Pest Species: Laboratory and Field Trials 1987
Dave Simser (1989) 18 pages
Cover Cropping and Green Manuring on Small Farms
in New England and New York: An Informal Survey
Mark Schonbeck (1988) 30 pages
The New Alchemy Institute is working towards an ecological future. Located on a 12-acre farm on Cape Cod, Massachusetts, New Alchemy promotes sustainable agricultural systems that restore ecological balance and help neighborhoods feed themselves. Through our research, education and networking programs, we seek to build whole systems that enhance environmental integrity and human well-being.
Current research projects at New Alchemy focus on biological pest control, cover crops, composting, greenhouse horticulture and organic market gardening.
We have created the Research Report series in order to make the results of our research available promptly after review in an affordable format. These Research Reports are intended to serve practitioners, homeowners, renters, small-scale farmers and other researchers and students. In addition to Research Reports, the institute also publishes a Technical Bulletin series that provides hands-on information to the practitioner and occasional longer works.
Founded in 1969, New Alchemy is a nonprofit organization supported
in part by membership fees. Membership benefits include the New
Alchemy Quarterly, access to our library, free admission for
tours, reduced tuition for courses and special events, and a 10
percent discount on books and products from our catalogue. For
further information about other publications, institute membership,
or to make comments and suggestions please contact:
The Green Center, 28 Common Way, Hatchville, MA 02536, USA