OSU Extension Service Portland Metro Area
Weston Miller- Community and Urban Horticulture Faculty
Address: 200 Warner-Milne Rd. Oregon City, OR 97045
Phone: 503-706-9193 Fax: 503-655-8636
Email: weston.miller@oregonstate.edu
Web: http://extension.oregonstate.edu/mg/metro
Season Extension for Vegetable Production
Learn the basics of season extension including: benefits/drawbacks, greenhouse management,
IPM, crop timing, and more. Session includes a tour of CCC season extension facilities.
Instructor: Weston Miller, OSU Extension Service
September 8, 2012. 3:30-5:00pm
Why season extension?
 Extend both ends of the growing season
 Prevent rain, wind, and hail damage,
 Reduce damage to crops and pesticide use (if you use pesticides)
 Avoid the loss of harvest days due to precipitation
Drawbacks of season extension
 Capitol costs to purchase and install structure(s)
 Increased labor costs from hand labor due to limited equipment access
 Environmental concerns: disposing of plastic . Don’t use PVC!
 Available market for produce?
 What about my winter vacation? You mean I have to be there every day?
General design/management considerations
• Typically unheated with passive heating and ventilation= cheapest options
• Account for snow load and wind load as primary design considerations
• Manage temperature- Avoid cold damage and heat stress
• Manage humidity- Minimize conditions that promote plant diseases by providing
ventilation and air movement
• Manage soil moisture- Provide at least 1” per week and manage salt build-up
• When in doubt, vent for cooler temperatures and air movement to reduce heat stress and
disease pressure.
• Buffer temperature swings by providing thermal mass such as water barrels and by
strategically opening and closing the vents at the beginning and end of each day as dictated
by daily weather and types of ventilation that you employ
• Keep the structure as cool and dry as possible.
Types of season extension devices
 Cloches and cold frames
 Floating row cover
 High tunnel/hoop house
 Caterpillar tunnel- Think sturdy hoops 4’ apart with plastic or row cover lashed down
Conestoga wagon style. Can be installed on sloped land
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Multi-bay tunnels- Imagine the possibilities!
Planting timing
 Four Season Harvest- Eliot Coleman (table 14- See handout)
 An Educators Guide to Vegetable Gardening- OSU Extension Service
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http://extension.oregonstate.edu/gardening/educators-guide-uses-gardening-learning-tool
Fall and Winter Vegetable Gardening in the Pacific Northwest- OSU Extension Service
http:// extension.oregonstate.edu/catalog/pdf/pnw/pnw548.pdf
Cloches and cold frames
 Small boxes with lids
 Wall of water
 Hot caps
 Colored plastic mulch- increase soil temperature and reflect light
Row Cover
Considerations for row cover
 Floating or supported? Heavy gauge wire, bent electrical conduit, other?
 Use rope purlin looped around hoops and securely fastened at ends to ground
 Thickness of covering? Choose medium to light thickness of material to optimize durability
and light transmittance. Medium thickness material (0.9 oz. per square yard protect to 26°F
and transmit 70% of the sunlight. Thinner material (0.55 oz. per square yard) gives some
frost protection (down to 28° F), transmits 85% of the sunlight. Thicker material (1.5 oz.
per square yard) is more durable, but only transmits 50% of the lite: good option to cover
sensitive plants in cold snap.
 How to connect to ground? Rocks/bags; boards, dirt, lashed (caterpillar tunnel)
 Black plastic mulch can allow less frequent weeding
 Drawbacks: out of site out of mind; additional labor time to deal with materials; slugs;
weeds; trapping pests under cover lead to major damage; disposal of materials
 How long to cover? 4-5 weeks for cool-weather crops; Longer for warm season; must
remove for pollination
Benefits of row cover
• Functions as a pest barrier too!
• Decreased need for hardening off transplants from greenhouse to field
• Early yields (brassica, leeks, endive 1-3 weeks early; melons 1 week)
• Increase yields up to (25% for cucurbits,,42 % for onions, 47% for peas, 60% lettuce)
• Frost protection (4-7°F)
• Pest protection: flea beetles, leaf miners, imported cabbage moth, aphids, carrot rust fly…
• Water conservation: mini water cycle occurs within fabric tent
• Must support in windy areas as movement can damage plants
• Mixed results with tomatoes and peppers
High tunnel/hoop house
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Design considerations
 Quonset or Gothic shape? (see diagram to right)
 Quonset: cheaper
 Gothic: more expensive; shed snow; more usable
space along walls; better ventilation b/c higher;
shed interior condensation rather than drip
 Perimeter to growing area ratio: Wider structures
have lower ratio and less heat loss and milder
temperature swings. Wider tunnels also tend to be taller
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Shape of Structure
and provide improved ventilation and interior air
circulation.
Extra purlins allow built-in trellising options
http://www.uvm.edu/sustainableagriculture/hightunnels.html
Site considerations
 Utilities- needed: water. Optional: electricity for heat mats and fans, propane for heating
 Access and room for expansion
 Snow loads? Wind loads?
 Gable end toward prevailing winds can reduce wind strain
 Avoid frost pockets
 Soil drainage is key
 For summer growing, N-S orientation provides minimal shading. Orient 10° to E from true
south to maximize morning heating
 For off-season growing, E-W orientation for increased solar gain and warmer overall
temperatures
Ventilation is key!- Avoid heat stress and moist conditions
 Roll-up sides for larger structures
 Gable-end vents and doors
 Automatic louvers
 Paraffin cylinder vent openers
 Electric fans: grid-connected and solar powered
 Shade cloth? Expensive; difficult to install; useful for propagation and tender plants
Bed layout
 With access vs. crop optimization
 Longitudinal
 Lateral with center aisle
 Edge effect around perimeter
Bed Layout for Production
http://www.uvm.edu/sustainableagriculture/hightunnels.html
Materials for end walls, doors, side walls, etc.
 Plastic lumber- durable; expensive; non structural
 Rot resistant woods- expensive; medium durability
 Fir and pine: cheaper and less durable
 Treated wood- expensive; durable; not for organic
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certification
Interior row covers A second layer of protection in the form of floating row cover or supported on wire or
hoops can provide additional protection
 Downside is that there is decreased light transmittance, which can lead to leggy crops
 Consider daily installation/removal as option for use
 Consider use as needed for extra protection
Irrigation under cover
 Drip systems make sense for transplanted crops like tomatoes, peppers, heading brassicas
and lettuce, and cucumbers
 Low-pressure micro sprinklers make sense for cutting greens and other direct-seeded
crops where T-tape will get in the way and also will not provide even soil moisture over
entire area for germination
Propagation in hoop house
 Use heat mats to decrease germination time and increase germination rate!
 Provide additional cover to conserve heat as needed
 Use sterile germination medium
 Sanitation to prevent build-up of disease. If you re-use flats and pots, consider sterilizing
materials with bleach or peroxide
 Timing is critical: transplant when roots established but before root bound
Integrated Pest Management (IPM) for season extension
 Manage climate (temperature, humidity, soil moisture, air movement) to minimize disease
pressure. Keep it cool with moving air.
 Provide proper cultural conditions for various crops
 Sanitation, sanitation, sanitation!
 Use crop rotation
o Avoid accumulation of soil-borne pests and diseases
o Don’t trap pest insects under your row cover.
 Choose adapted and disease-resistant varieties where available
 Monitor plants regularly
 Judicious use of least-toxic pesticides and fungicides
Resources:
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2012 EQIP Seasonal High Tunnel Initiative
http://www.or.nrcs.usda.gov/programs/eqip/fy12/high_tunnel.html
High Tunnels- University of Vermont Center for Sustainable Agriculture
http://www.uvm.edu/sustainableagriculture/hightunnels.html
Four Season Harvest- Eliot Coleman
Grow Food in Your Polytunnel-Mark Gatter and Andy McKee
Gardening Under Cover- William Head
Organic Gardening Under Glass- George and Katy Abraham
WSU Community Fact Sheet #19
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