High Tunnel Crop Talk Notes March 26, 2012
We held the first High Tunnel Crop Talk today! A summary of our discussion is below. (Participants, please let me know if there’s a need for any corrections; I’ve done my best but may have missed or misunderstood something – Liz.)
Join us again in two weeks, April 9, 2012, 12:30 – 1:30 p.m. Eastern/11:30-12:30 Central. Point your web browser to https://gomeet.itap.purdue.edu/htct/ and click on the phone icon to be dialed in to the call, or dial 1-866-492-6283. Tony Bailey from NRCS will join us to talk about the EQIP program for high tunnel grants in Indiana.
Report: Matt Rudisill’s research on how organic fertility amendments are mineralized in the soil is getting underway for the second season at Purdue’s Meig’s Research Farm near Lafayette. He is comparing nutrient release from different sources, including composted chicken manure from Rose Acre Farms and plant-based amendments. Last year the plant-based source was alfalfa meal and this year it will be a cover crop of hairy vetch, plus additional alfalfa meal if needed. The hairy vetch grew very well over winter and is still growing in the tunnel. Bell pepper seedlings are getting started in a greenhouse and will be transplanted to the tunnel later. At this time he is taking soil samples in the greenhouse.
Report: At an organic farm in Ohio, preparation is underway for two new tunnels, 20-ft. wide, to be used for both summer and winter crops. The tunnels, from Tunnel Vision Hoops, will have retractable dome ends that allow for more space and handle winds better. Double poly will be used, with blocks between the layers to provide an air pocket that will provide additional insulation.
Question: is 20 ft. wide enough to maintain heat in the structure for winter crops?
A smaller structure will lose heat more quickly, but will also warm up more quickly. (Shubin Saha)
The Virtual Grower program can be used to estimate heating costs for greenhouses of various sizes and construction. It was developed by Jonathon Frantz, USDA/ARS in Toldeo and may be downloaded from http://www.ars.usda.gov/services/software/download.htm?softwareid=309. See the end of this post for example calculations related to this question. (Liz Maynard)
Report: Tunnel-grown organic fall-bearing red raspberries in Ohio are 3 to 4 inches tall. They are grown on a TGS trellis system. The raspberries are in their fourth season. They have done well until last year when yellow rust significantly decreased production. Canes have been cut back and roses along fence line removed. A soil test showed need for additional nitrogen so compost was applied and red clover was sown in the aisles. The berries are mainly sold wholesale to grocery stores, with a few to restaurants and farmers market.
Report: Shubin Saha, Vegetable Specialist located at Southwest Purdue Ag Program (SWPAP) in Vincennes, has two of three 30X96-ft. structures ready for production this season at SWPAP. He will be doing a replicated tomato variety trial this year. The varieties include 7 indeterminate (Big Dena, Panzer, Arbizon, New Girl, Estiva, Imperial 643, and Potenza) and 2 determinate (Rocky top and Red Deuce). He is emphasizing inderminate varieties because they make better used of the vertical space. Tomatoes are on 5-ft. centers, 2-ft. in-row spacing. Seed companies represented include Syngenta, Enza Zaden, Johnny’s, and Harris Moran. He is finishing up fertilizer application in the tunnel and will soon be laying plastic mulch.
Question: How do you spray tomatoes in high tunnels?
Create a trellis. Remove lateral shoots on tomato plants so there is just a single stem. Use a braided steel cable down center of row. Drop a string down from cable (‘Tomahook’ and other spool systems are available) and train tomato along it. As tomato grows and fruit are harvested, lean and lower tomato plants.
For spraying, Shubin has used a backpack sprayer in the past. This year he has developed a sprayer that can be pulled through the high tunnel. It is based on a garden cart, has a mixing tank, battery for the pump, and boom with nozzles spraying parallel to the ground. (Shubin Saha)
Diseases likely to be found on tomatoes in greenhouse include early blight, leaf mold, and bacterial diseases. Management recommendations are available in the tomato section of the Midwest Vegetable Production Guide for Commercial Growers, ID-56 http://www.btny.purdue.edu/Pubs/ID/ID-56/. On page 12 materials for use greenhouses are listed http://www.btny.purdue.edu/Pubs/ID/ID-56/GreenhouseTunnel.pdf. (Dan Egel)
Question: What happens to tomatoes when it gets down into the 40’s or high 30’s? Would it make sense to put a propane construction heater in the tunnel?
When it gets below 50°F tomato growth slows down. Wouldn’t recommend a construction-type propane heater in the tunnel. (Shubin Saha)
Question: How do you avoid condensation in the greenhouse? Other than venting, is there any solution?
When using two layers of poly with a fan blowing air between the layers, set the fan to pull air from outside the greenhouse, not from inside the greenhouse. This will reduce condensation between the layers of plastic. To reduce condensation inside the greenhouse, vent, especially just before the end of the day. (Shubin Saha and Liz Maynard)
Greenhouse films with anti-condensation properties are available. They have an additive so that drops don’t form and the water rolls down the plastic instead of dripping. Several brands are available. (Roy Ballard)
There are also products that can be sprayed on to reduce drop-formation; they do rinse off over time. One example is Sun Clear. (Liz Maynard)
Question: What are some good resources for someone starting to research high tunnel structures and production?
The Purdue Fruit and Vegetable Connection has links to recorded programs on high tunnels, and key sites at other states. See http://www.hort.purdue.edu/fruitveg/veg/plast.shtml .
Report: Liz Maynard reported on two 48X30 rolling high tunnels under construction at the Pinney-Purdue Ag Center in Wanatah. Work is beginning on shallow trenches for the rails on which the wheels attached to the bottom of the structures roll.
Resource: This publication might be of value especially if you are using compost or manures in your production system. It discusses potential for carryover of particular herbicides in compost and manure. (Roy Ballard)
Example calculations from the Virtual Grower Program (see above)
The Virtual Grower program doesn’t exactly answer the question posed today – how much colder would a 20-ft.-wide greenhouse be than a 30-ft.-wide greenhouse – but it can answer the question how much more would it cost to heat a 20-ft greenhouse than a 30-ft. greenhouse. If one greenhouse costs more to heat than another, than without heat it would be colder. The table below shows relative heating costs to maintain a minimum temperature of 30°F in various double-poly greenhouses, 16 ft. tall with 4-ft. sidewalls and corrugated polycarbonate end walls, in Toledo, Ohio. The calculations were done using Virtual Grower 3. The 100 X 30 ft. greenhouse costs more to heat because of the increased area, but costs the least on a per square foot basis. Comparing the 100 X 20 and the 67 x 30 structures, both about 2000 sq. ft., the 67 X 30 costs slightly less to heat. The cost assumes a propane heater operating at 45% efficiency and propane at $2.40/gallon.
Length X Width (ft.)
Total Area (sq. ft.)
Cost per Year ($)
Relative Cost per Sq. Ft.
100 X 20
100 X 30
67 X 30
Name: email (all @ purdue.edu)
Liz Maynard, Horticulture Specialist at Purdue in Valparaiso: emaynard
Dan Egel, Vegetable Pathologist at Southwest Purdue Ag Program in Vincennes: egel
Shubin Saha, Vegetable Specialist at Southwest Purdue Ag Program in Vincennes: ssaha
Roy Ballard, Purdue Extension, Hancock County: rballard
Note: Mention of specific products does not constitute endorsement by Purdue University.