High TunnelsFEATURES, CONSTRUCTION, PRINCIPLES, AND PRACTICAL MANAGEMENT

RACHEL RUDOLPH, PHD

FEBRUARY 26, 2018

OverviewDefinition and justificationDesign considerations and featuresSite selectionPrinciples of Season ExtensionManagement

DefinitionWHAT IS CONSIDERED A HIGH TUNNEL

DefinitionA high tunnel, also known as a “hoop house,” is a covered structure used to cover and protect crops from sun, wind, excessive rainfall, and/or cold.

High tunnels are typically passively heated or cooled, but many growers install fans and heaters.

Why use a high tunnel?High tunnels can improve aspects of vegetable production compared to an open field, such as:Extend the growing season, both spring and fallPlanting and harvestingImprove fruit quality Reduce nutrient and pesticide transportationProtect plants from severe weatherGrow a lot in a relatively small space

Design considerations

Design considerationsDimensions

Bow spacing

Structure material Metal vs. wood

Single vs. double layer plastic

Ventilation

Irrigation systemBudget Photo credit: Krista Jacobsen

DimensionsDimensions

12 ft x 40 ft—good for a backyard/small parcel of land

30 ft x 96 ft is relatively standardNRCS EQIP

30 ft x 72 ft also commonNRCS EQIP

Photo courtesy of UNL High Tunnel manual.http://extensionpublications.unl.edu/assets/pdf/ec308.pdf

Structure options

Quonset

Gothic

Multi bay

Photo credit: Krista Jacobsen

Photo credit: Fruit Grower News

Photo credit: Krista Jacobsen

Bow spacingCan be anywhere between 3ft and 6ftbetween bows

4 ft is recommended for KY

Snow in the winter can cause the tunnel to collapse in on itselfCloser bow spacing helps prevent the plastic cover from sagging under snow weight

Photo courtesy of UNL High Tunnel manual.http://extensionpublications.unl.edu/assets/pdf/ec308.pdf

EndwallsShould accommodate equipmentThink about height and width of necessary

equipmentOr standing height for a person

Facilitate ventilation

Doors and venting options

Photo credit: Krista Jacobsen

SidewallsAlso known as side curtains

4-8 ft heightsThe higher the better for ventilation purposesAt least 6 ft recommended if possible

Roll-upDrop down

Hybrid approaches

Photo credit: John Walsh

CoveringDifferent cover material available

Most common is 6 mil polyethylene1 mil = 0.001 inch6 mil = 0.006 inch

6 mil poly usually needs to be replaced every 4-5 yearsCover should be put on in warm weather so the plastic stretches over the frame

Photo credit: John Walsh

VentilationSidewalls and endwalls are critical components ventilation

Other ventilation options includeButterfly / Endwall vents (A)Ridge vents (B)

IrrigationConsider 1 line for every 1-2 rows of crops

8”-12” emitter spacing will work for most transplanted crops

4” emitter spacing can be useful on crops with long germination times on well drained soils (carrots)Re-using tape is much easier than in the field

Photo credit: Brett Wolff

Other featuresShade clothMade from woven fabric or plasticReduces light transmissionCan help reduce stress from high

temperaturesCan help lessen frequency of

abiotic disorders such as sunscald, blossom end rot, and cracking

Photo credit: Shubin Saha

Other featuresMoveable

Site selection

Site selectionLocation

Tunnel orientationWindSun

Access to electricity and waterMay not need electricity, but will definitely need water

Site preparationSoil typeDrainage

LocationKnow your soil and your land

Are there low spots?

Are there areas with poor drainage?

Photo credit: Shawn Wright

Tunnel orientationSunEast-west—more overall lightNorth-south—more uniform light distribution

WindPrevailing winds should be parallel with the tunnel Winds hit the doors, not the sides to avoid frame

damageGround posts set in concrete is safest for high wind

sites

If choosing between wind and sun, orient according to the wind

Photo credit: Krista Jacobsen

Site preparationDrainageDepends on soil type and topographyKnow your soilhttps://websoilsurvey.sc.egov.usda.gov/App/Home

Page.htm

Soil preparation Grading and deep tillage should be done before

construction beginsMake sure the floor within the tunnel is level Fertilizer and water will flow to the low spot,

resulting in uneven growth

Photo credit: Krista Jacobsen

Principles of Season Extension

What is season extension?Any method or technique that allows a crop to grow beyond its normal outdoor/open field growing seasonExample: Tomatoes in November in Kentucky

Advantages of season extensionPossible year-round incomeRetention of old customersGain in new customersHigher pricesHigher overall yieldsBetter qualityExtended employment for workers

Disadvantages of season extensionNo break in yearly work schedule

Increased management demandsMust be attentive to inside temperatures (rolling sidewalls up or down)

Higher production costsGas, Electricity, Materials

Plastic disposalCost, Location, Method

Key practices of season extensionSite selectionSouth-facing will stay warmer in the fall and warm up sooner in the

spring

Cultivar selectionNumber of days to maturityCold hardinessHeat tolerance

Use of transplants (vs. direct seed)Can provide a head start to the season, as much as 4 weeks

Key practices of season extensionPlastic mulch useBlack plastic raises soil temperatureWhite plastic keeps soil temperatures lower

Row cover useFloatingHoop-supported Gives extra cold protection in a high tunnel

Shade clothExists in various % (densities)

Photo credit: Krista Jacobsen

ManagementFACTORS TO KEEP IN MIND AND BASIC STRATEGIES

Soil samplingCollect soil samples annually for testing (for spring production, collect in the fall) Routine soil test includes: pH, buffer pH, P, K, Ca, Mg, Zn for $7 (free in some counties) Request soluble salts (SS) for an additional $4 CEC and base saturation

Learn how to interpret the results of the soil testWhat does each value really mean?

Apply only the nutrients needed based on your soil and the crop you intend to grow

Split applications of fertilizer

Consider foliar testing

Save $$$

EXAMPLESRecommendations for Phosphorus: 31-60 lbs/acre

Recommended pH:6.5-6.8

Soluble salts

The soluble salts test measures the electrical conductivity (EC) of a water-soil paste

The EC of a soil is a representation of the amount of dissolved salts from the soil

Soil salinityMeasure of soluble salt content—anions and cations that are soluble in water

Contributors include: Na, Mg, Ca, K, nitrates, chloride, sulfate Salts originate from the weathering of soil minerals, but can be introduced as

fertilizers

Because high tunnels are typically covered with plastic throughout the year, rain is not able to affect the soil as it does in an open field environment Nutrients and salts may build up near the soil surface or crop root zone

EC reading (mmhos/cm or dS/m)

Evaluation Interpretation

0-0.40 Very low Nutrient levels too low for normal growth

0.41-0.80 Low Suitable for seedlings and salt sensitive plants

0.81-1.20 Normal Standard range for most established vegetable crops; upper range for salt-sensitive crops

1.21-1.60 High Possible reduced vigor and growth, particularly during high temperatures

1.61-3.20 Very high Possible visible salt injury and reduced growth, including marginal leaf burn and wilting

>3.20 Extreme Visible salt injury on most vegetable crops

Sanchez and Ford, 2018

Salinity preventionLimit compost and manure applications

Limit nitrate applications

Only apply nutrients needed for the crop See ID-36 for guidelinesGet annual soil tests

Split applicationsDoes not add all nutrients at once

Cover croppingAdds organic matter Scavenges nutrients

Photo credit: Krista Jacobsen

Salinity remediationOverhead irrigate when crops are not growingWill take a considerable amount of water

When changing plastic layers, allow rain on high tunnel soil for a couple of months

Cover croppingCover crop will take up extra nutrients Seed cover crop, allow to grow, mow/cut, and

rake outDo not incorporate cover crop

California Fertilizer Association, Western Fertilizer Handbook, 8th Ed.

Water volume

Percent of salts leached below 12’’

6’’ 50%12’’ 80%24’’ 90%

Crop managementCrop rotationRotate out of crop families every year

Crop spacingUsually tighter than open field planting Seed heavy then thin out later Tighter spacing may lead to more disease/pest

pressure

Photo credit: Rachel Rudolph

Crop managementPlanting windows Successional planting/seeding for continuous

availability

Transplanting vs. direct seeding

Consider crops that allow for multiple harvestsTomato vs. cabbage

Photo credit: Rachel Rudolph

Temperature managementDiversified high tunnels can be difficult to manage at transition times

Cool-season and warm-season crops have different temperature requirements

Need to prioritize which crop(s) you are managing for if growing everything in the same house

If selling, what is your new crop, what crop will make you more money?

Photo credit: Rachel Rudolph

Additional resourcesBasic production informationUK ID-36 Vegetable Production Guide for Commercial GrowersUK ID-235 IPM Scouting Guide for Common Problems of High

Tunnels…www.hightunnels.orgEliot Coleman’s “New Organic Grower” and “Winter Harvest

Handbook”Paul and Alison Wiediger’s “Walking to Spring”Trade publication “Growing for Market”