Season Extension Options - Making the Right Choice for Your Farm, Gardening Guidebook for Maine

Laying plastic mulch and trickle irrigation line. Photo by Caragh Fitzgerald, The University of Maine

Season Extension Options: Making the Right Choice for Your Farm

There are many options available for produce growers to extend their growing seasons. This brief article describes some of the options and factors to consider. As with most farm activities, success or failure will depend on the details of the materials, management and implementation. The resources listed at the end of the article provide you with many of these details. Other farmers, Cooperative Extension personnel, consultants, and vendors will also be valuable resources to help with your decision-making.

Season extension techniques allow you to grow your products for longer than they can be grown under typical conditions in the field. In the Northeast, these techniques focus on getting a crop to produce earlier or continue later in the season. Some techniques also allow for “winter harvest” of cool season crops. Direct benefits of season extension include: getting a product to market earlier, when prices are higher; being able to harvest a warm-season crop that typically performs inconsistently due to cool weather; and having a longer harvest period overall. Other benefits may include a reduction in weather, pest, and disease damage, lower control costs, and improved quality. FINDING A GOOD FIT FOR YOUR OPERATION How do you decide what, if any, season extension techniques are the best for you? Inexpensive techniques can be tested on a small scale with little risk beyond time, energy, some plant material, and a little bit of money. But before investing in a costly alternative, such as a high tunnel or a greenhouse, you should carefully weigh the value of the technology and its costs.

Diverse crops in high tunnel: raspberries, tomatoes, and strawberries. Photo by Mark Davis

Page 2 Extending the Production Season

Before you invest heavily in season extension methods,

consider:

• What you want to achieve • Where you will sell your

products • The price you need to charge • The time, money, labor, and

technology requirements • How it will affect other aspects

of your farm

High tunnel under construction. Photo by Caragh Fitzgerald, The University of Maine

First, decide what you want to achieve. 1. What new crops do you want to grow

or which ones do you want to grow differently? Be sure there is a market for these products. Don’t skip number 4.

2. When will you be growing? Some high tunnels and greenhouses are designed to support or shed a winter’s snow load. But, they are much more expensive per square foot than row cover and/or plastic over low tunnels or caterpillar tunnels. If you aren’t growing or harvesting crops when there is likely to be snow, then you can use a less sturdy (and less expensive) structure.

3. When will the new market season be? It is easier to add a product to an existing market outlet than it is to develop a new market or buyers.

4. What price can you charge for your products? Will you be able to recoup the higher cost of production from using the season extension technology? Keep in mind that there can be benefits that are hard to calculate. You may not make much money on a specific item, but if it draws customers to your farm stand, then it can increase overall income.

5. What will you need to implement this technology successfully? Irrigation under the plastic mulch? Time and equipment to bend hoops for low tunnels? Labor and equipment for high tunnel construction? Sometimes farmers (and others) will purchase new equipment with the best of intentions, only to find out that they don’t have the time to install it or to learn how to use it effectively.

6. Can your farm accommodate something new now? New methods can create a mental and emotional drain as you learn how to implement them. They may take personnel or funds away from other parts of the farm, perhaps leaving those areas critically unsupported. Field and pest management activities will be different. Structures may

need frequent monitoring, even multiple times a day. Yield reductions or crop losses are possible if temperatures get too high or if high winds destroy the structure. This is especially true for those structures that are passively ventilated. While none of these demands is a deal-breaker, it is important to keep these points in mind. If you or your farm business is already struggling, a significant new undertaking might be helpful, or it might strain the situation to the breaking point.

Making the Right Choice for Your Farm Page 3

Black plastic mulch covering no-frame raised beds. Photo by Caragh Fitzgerald, The University of Maine

TECHNIQUES No-cost or very low-cost options. Some methods of season extension are free or very inexpensive. They may also require little or no cost or equipment. These include:

• Field selection. Take advantage of southern-sloping fields that warm fastest in the spring. Avoid planting your earliest, most tender crops in low areas, since this is where the cold air will sink. Soil that dries out quickly will warm faster than a heavy, wet, high-clay soil.

• Variety selection and planting dates. Choose varieties that are more heat- or cold-

tolerant to extend the harvest season. Many seed catalogs now recommend certain varieties for season extension or for growing in high tunnels. Succession planting can also ensure harvestable product later in the season.

• Transplants. For plants that will grow well from transplants, use them to give you a

head start on the season. By the time the soil and weather warms sufficiently for outdoor growth, you will be putting a small plant out, not a seed.

• Wind breaks. Wind breaks can create a small area with locally warmer conditions.

Small grains, perennial grasses, trees, or a fence may help to block crops from early-season winds. Careful selection must be made to be certain that the wind break is of sufficient height to be effective and that it does not shade the crop or compete for water or nutrients.

• Raised beds. Soil in raised beds will dry and warm faster than soil that is flat in the

field. Home gardeners often use frames to contain the soil of their raised beds, but no-frame raised beds are more practical for commercial production. Bed heights of 6-8 inches are common.

Mulch. Plastic mulches are used to raise the temperature of soil beneath them. Much of the temperature increase occurs when the plastic is in direct contact with the soil, so it is important that the plastic is laid tightly against the soil. Black plastic mulch suppresses weed growth and will raise daytime soil temperature. Compared to bare soil, the temperature will be about 5° higher at 2 inch soil depth and 3° higher at 4 inches. IRT (infrared-transmitting) plastic raises soil temperatures more than black plastic. It also transmits more light, so weed suppression is reduced. In some parts of the country, colored plastic mulches have been shown to reduce insect incidence. This has not been shown to be true in Maine. Plastic mulches conserve water, but many growers, especially those on sandy soils, will use trickle irrigation under the plastic to provide adequate moisture.


Peppers getting an early start in a low tunnel. Row cover is supported by wire hoops. Note plastic mulch. Photo courtesy of Johnny’s Selected Seeds.

Biodegradable mulches are also available. They tend to be more expensive, but recent research shows that some types provide soil-warming and weed-suppression similar to black plastic. For more information about biodegradable mulches, see http://www.newenglandvfc.org/pdf_proceedings/biomulches.pdf Other mulches, such as straw or newspaper, are good at conserving soil moisture, and they can also help suppress weeds. However, they will keep soils cooler than if the ground were bare. Row cover. Row cover is translucent spun-bonded material. The lighter weights of this material are often used as a physical barrier to insects. Heavier weights of the material will keep the temperature of the enclosed area elevated. These materials can be applied in long narrow rows to cover one or two beds, or they can be used in large sheets. It is important to secure the edges, or else the row cover will blow away. The thicker the row cover is, the more heat it will retain. The thicker materials also allow less light to penetrate, so you will need to strike a balance between heat retention and light. If you use heavy weight materials, you will also have to be careful that temperatures don’t get too high for the plants underneath. The lighter weight materials can be laid directly on most plants without support. Some plants, such as eggplant and pepper, have sensitive growing points, though, which may be damaged without support. Plastic cover. Plastic cover is even more effective at raising and retaining heat than row cover. But, it does not allow any water in, and plants can be “cooked” if the enclosure is not vented. Venting by lifting or removing plastic by hand can be time-consuming, so some farmers use slitted or perforated plastic covers. When temperatures are cold, the slits are mostly closed. When temperatures under the plastic heat up, the hot air rises through the pre-cut slits in the plastic. If plastic is being used to keep frost off the plants, it must not be allowed to touch them. Low tunnel. Low tunnels are structures built from short (usually less than 3 feet high) supports that hold plastic or row cover above the plants. The cover can then be used to protect the plants from frost, since the material is not touching the plants. The supports will prevent any potential distortion in plant growth from contact with the cover. The cover still needs to be secured on the ground. Depending on your area’s snow load, the material used for the supports, and the spacing of these supports, low tunnels may or may not be able to withstand winter snows. Walk-in or caterpillar tunnel. Walk-in or caterpillar tunnels use still taller supports. They are typically between 8’ and 18’ wide, around 6’ or more tall, and 24’ to 300’ long. The cover (plastic or row cover) is held above the supports by a rope between the centers of the supports and by ropes crossing between the supports from side to side. Ventilation is


High tunnel with raised beds. Note roll-up sides. Photo by Caragh Fitzgerald, The University of Maine

Walk-in or caterpillar tunnel. Photo courtesy of Johnny’s Selected Seeds.

necessary to keep the crops from overheating. This is achieved by pushing the cover up along the sides. Friction keeps the cover up, although sometimes clamps or other techniques are needed. The type and spacing of supports will influence the structure’s ability to withstand high winds and winter snows. High tunnel/hoophouse. High tunnels (or hoophouses) were originally envisioned as a low-cost alternative to greenhouses. They consist of hoop-style supports covered with plastic. The structures are tall, typically 6 feet or higher at the center. The plastic is attached

in a way that the sides can be either rolled up or dropped down for ventilation. High tunnels protect the crops from some of the season’s later or earlier frosts. They are often used to enhance the production of warm season crops as well as growing and holding cool season crops for winter harvest as made popular in Eliot Coleman’s book Four Season Harvest. Many structures have no heat or electricity. This is a highly-adaptable type of structure, though, and farmers have designed many modifications by using a variety of materials, adding supplemental heat sources, and using fans for supplemental ventilation. You may also include other season extension techniques in a high tunnel, such as plastic mulch, row covers, or low tunnels. In Maine, the weight of the snow is a very serious concern for high tunnel owners. Some designs (gothic vs. Quonset) and materials (galvanized pipe vs. PVC pipe) are better than others at withstanding the weight of winter snow. Removing the plastic in the fall eliminates the possibility of collapse for a weaker high tunnel. You may also roll the plastic up to the peak of the house and secure it there. Although high tunnels were originally designed to not have heat, some farmers have installed supplemental heat. Techniques range from a wood or corn stove to in-ground heat provided by propane, waste vegetable oil, or solar hot water. If you are considering adding supplemental heat, first carefully evaluate the economic benefit you hope to gain and the cost of the system. Then, be sure to watch your crops carefully to be sure that you don’t create other production problems with this heat source. Conventional greenhouse. While some of the techniques discussed above may be described as low-input greenhouses, a conventional greenhouse will have electricity and heat. Because of the type and number of crops grown, the production often occurs in flats or pots on tables or benches, rather than in the ground. With a conventional greenhouse, you can


Greenhouse showing intensive production methods and diverse crops. Furnaces are at both ends of the greenhouse. Photo by Mark Hedrich, Agricola Farms

grow plants far beyond their typical production period. Plant growth in a greenhouse is rapid, and pest development can be rapid also.

Because of the cost of materials and equipment, a conventional greenhouse is expensive to set up and maintain. Carefully evaluate the needs of your crops to be certain a conventional greenhouse is warranted. You should also develop a good marketing and business plan. There are many greenhouse styles, materials (supports and covering), benches, heat sources, lighting, and ventilation options to consider. Consult the references at the end of this article for more specific information and links. There have been a number of case studies written about heating options for Vermont

greenhouses. See http://www.uvm.edu/vtvegandberry/energylinks.html for links to these reports. ESTIMATED COSTS OF VARIOUS SEASON EXTENSION TECHNIQUES These estimates are provided for general planning purposes only. Actual costs are extremely variable, and depend on specific materials, amounts or sizes purchased and used, and labor. Do your research! $ Plastic mulch, row cover, plastic cover, low tunnel: less than $0.10/ft2 material. Additional costs are likely (such as trickle irrigation, supports, staples or pins to secure material). The amount of row cover or plastic cover needed will often be greater than the square footage covered, since the material will be raised over plants or supports.

$$ Walk-in tunnel: less than $0.50/ft2.

$$$ High tunnel: less than $1.00 to $3.00/ft2 or more.

$$$$ Conventional greenhouse: $3.00 to $10.00 or more/ft2.

(Values from costs from commercial suppliers, January 2011; Blomgren and Frisch, 2007; Diver, Steve. 2000. Organic greenhouse vegetable production. ATTRA/NCAT. http://attra.org/attra-pub/ghveg.html) SUMMARY There are a variety of techniques that can help you extend your production or harvest season. These will allow you to increase the number of products available and/or the period they are available. Choosing the technique(s) that will work for you depends on what you want to achieve, the markets available to you, the price you can charge, the requirements of the technology, and your ability to incorporate something new. Many farmers have found these techniques to be important to their overall profitability. Careful research, experimentation, and record-keeping will tell you if one or more is a good fit for you.


High tunnel showing intensive vegetable planting to maximize use of space. Photo by Caragh Fitzgerald, The University of Maine

RESOURCES On-line publications Bachman, Janet. (2005) Season extension techniques for market gardeners. ATTRA/NCAT. http://attra.ncat.org/attra-pub/PDF/seasonext.pdf 42-page publication outlining cultural practices, plasticulture, and economics of season extension. Blomgren, Ted and Tracy Frisch. (2007) High tunnels: using low-cost technology to increase yields, improve quality, and extend the season. Produced by Regional Farm and Food Project and Cornell University with funding from USDA Northeast Sustainable Agriculture Research and Education. http://www.uvm.edu/sustainableagriculture/hightunnels.html 77-page manual focusing on high tunnels, but also including walk-in tunnels and low tunnels. Sections on marketing, site considerations, selecting a structure, construction tips, environmental management, soil and crop management, and pest management. Six case studies. Healy, Will, James Hanson, and Stanton Gill. (no date) Starting in the greenhouse business. Fact Sheet 593. Maryland Cooperative Extension. http://extension.umd.edu/publications/pdfs/fs593.pdf 8-page fact sheet including lists of crops, outlining types of production, site selection, costs of construction (1990 prices). Roos, Debbie and Doug Jones. (no date) Season Extension. North Carolina Cooperative Extension, Chatham County Center. http://www.ces.ncsu.edu/chatham/ag/SustAg/SeasonExtensionOctober2005a.pdf 16-page publication describing the mechanisms of season extension, cultural practices, fabrics, and structures. Print/video publications High tunnel production manual. 2nd edition. (2003) Center for Plasticulture. The Pennsylvania State University, University Park, PA. Construction and maintenance, planting, irrigation, environment, pest management, nutrient management, mulching, crop production (vegetable, berry, cut flower, sweet cherry), economics, marketing, organic methods, heating with waste plastics. http://plasticulture.psu.edu/node/115 book order information. Blomgren, Ted and Tracy Frish, producers. (no date) High Tunnels. Using low cost technology to increase yields, improve quality, and extend the season. Produced by Regional Farm and Food Project and Cornell University with funding from USDA Northeast Sustainable Agriculture Research and Education. 43-minute video featuring 6 farms in 5 northeastern states. http://www.uvm.edu/vtvegandberry/Videos/hightunnelvideo.html DVD order form. Byczynski, Lynn, ed. (2009) The hoophouse handbook: growing produce and flowers in hoophouses and high tunnels. 2nd edition. Growing for Market (single issue magazine). Farmer experiences, materials, design, construction. Coleman, Eliot. (2009) The winter harvest handbook. Chelsea Green Publications. Schedules, “cold” and “cool” greenhouses, crop types, greenhouse design, cropping methods, pests, marketing and economics, and tools.


Coleman, Eliot. (1992) Four-season harvest: organic vegetables from your home garden all year long. Chelsea Green Publications. Written for home gardeners, but useful information about cold frames and mobile high tunnels, as well as planting schedules. Web Links Construction of high tunnels: Resources for organic farmers. http://www.extension.org/article/18369 eXtension. Brief article and links. Cornell University High Tunnels http://www.hort.cornell.edu/hightunnel/index.html Cornell University. Links to sections about structures, crops, business and marketing. Energy information for vegetable and berry growers. http://www.uvm.edu/vtvegandberry/energylinks.html University of Vermont Extension. Includes case studies of greenhouse heating options. Greenhouse. http://newfarm.osu.edu/crops/greenhouse.html Ohio State University. Links to information about greenhouse production. Greenhouse crops and floriculture. http://umass.edu/umext/floriculture/fact_sheets/business_management/resources_bus_mgt.html UMass Extension. Resources for starting a Massachusetts greenhouse business. Hightunnels.org. http://www.hightunnels.org/ Project of K-State Research and Extension, University of Missouri Extension, and University of Nebraska Cooperative Extension. Information for educators and growers. The Pennsylvania State Center for Plasticulture. http://plasticulture.psu.edu/ Pennsylvania State University. Links to research and information about crops, plastic mulches, high tunnels. Worldwide Greenhouse Education. http://www.uvm.edu/wge/ University of Vermont, University of Florida, University of Arizona, Ohio State University, USDA/CSREES. Educational materials and links. Written by:

Caragh B. Fitzgerald Assistant Extension Professor University of Maine Cooperative Extension [email protected] 622-7546, 800-287-1481 (toll free in Maine) January, 2011

Reviewed by:

Mark Hutchinson, Associate Extension Professor, University of Maine Cooperative Extension Richard Kersbergen, Extension Professor, University of Maine Cooperative Extension

Produced with funding support from