Season Extension Options - Making the Right Choice for Your Farm, Gardening Guidebook for Maine ~ Maine Rural Partners ` For more information, Please see websites below: ` Organic Edible Schoolyards & Gardening with Children = http://scribd.com/doc/239851214 ~ ` Double Food Production from your School Garden with Organic Tech = http://scribd.com/doc/239851079 ~ ` Free School Gardening Art Posters = http://scribd.com/doc/239851159 ~ ` Increase Food Production with Companion Planting in your School Garden = http://scribd.com/doc/239851159 ~ ` Healthy Foods Dramatically Improves Student Academic Success = http://scribd.com/doc/239851348 ~ ` City Chickens for your Organic School Garden = http://scribd.com/doc/239850440 ~ ` Huerto Ecológico, Tecnologías Sostenibles, Agricultura Organica http://scribd.com/doc/239850233 ` Simple Square Foot Gardening for Schools - Teacher Guide = http://scribd.com/doc/239851110

1. 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

2. 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.

3. 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.

4. Page 4 Extending the Production Season
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

5. Making the Right Choice for Your Farm Page 5
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

6. Page 6 Extending the Production Season
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.

7. Making the Right Choice for Your Farm Page 7
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.

8. Page 8 Extending the Production Season
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
cfitzgerald@maine.edu
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