Experience with growing tomatoes in high tunnels: Irrigation, training and temperature management

Tomatoes are one of the more popular crops to produce in high tunnels, but may also be one of the more difficult. To be successful, growers must step up their level of management.

Tunnels have made a big impact on production, especially for small-scale producers. High tunnels extend the season, improve yield and quality and make organic production easier for some crops. This is the fourth report on my observations from seven years of conducting high tunnel tomato trials at the Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor, Mich. (Read the first report on insects, diseases and weeds; the second report on crop rotation; and the third report on fertilization, quality and yield.)

Some of the positive aspects of high tunnels – exclusion of rain and dew, reduced wind, and increased temperature – can be potential drawbacks. Plant management in tunnels is several steps more difficult than field management in the sense that a high tunnel system is less forgiving. Slight mistakes made in the field generally are not a problem, but slight mistakes or accidents in a tunnel can lead to major losses, especially for irrigation.


The only water plants receive in a tunnel is what growers give them. Exclusion of natural rainfall means there is little soil moisture reserve outside the irrigation wetting zone (typically a drip system). This is magnified even more in a container system. Growers need to pay close attention to daily water rates and system operation. Water amounts need adjusting often as plants grow, flower and eventually set and mature fruit. Water delivery cannot be interrupted for even short periods. Growers often automate high tunnel irrigation, but the system still requires daily monitoring to avoid failures. Tomatoes are quite drought-tolerant and missing one or two watering periods generally does not significantly affect plants, but it can seriously affect fruit.

Lack of water followed by a return to adequate levels often leads to fruit cracking (Photo 1). The best way to prevent cracking is to maintain a constant water level. Insufficient or inconsistent water can also promote blossom end rot, another condition often seen in tunnel-grown tomatoes (Photo 1).

Fruit cracking Blossom end rot
Photo 1. Fruit cracking (left) and blossom end rot (right) in tunnel-grown tomatoes.
Photo credit: Ron Goldy, MSUE

Growing indeterminate varieties

High tunnels provide producers the opportunity to grow indeterminate, greenhouse varieties that have longer production periods. However, they will need trellising, not just staking. Many growers try indeterminate types and use the tunnel ribs for support rather than establish a trellis. This is not a good idea since these ribs are not designed to carry the weight.

If you grow indeterminate types, you will quickly discover they need daily attention. They need to be pruned, cluster thinned, plants supported with clips (Photo 2), fruit supported with truss hooks (Photo 2), pests scouted and controlled, and fruit harvested. It would not be unusual for growers to be doing something daily to the plants starting from the time they flower.

Clips Truss hooks
Photo 2. Clips used to attach plants to support strings (left), and truss hooks (right) used to
keep fruit trusses from breaking off the plant. Photo credit: Ron Goldy, MSUE

Avoiding excessive heat

Another observation is in mid-summer in southwest Michigan, tunnels are too hot for good tomato production. My plants are generally transplanted into the tunnels in early May. Plants have always grown well until early July when growth slows and they stop setting fruit. Plants then improve in mid- to late August. Excessive heat that often occurs during this period causes flower clusters to drop without setting fruit. Daytime tunnel temperatures can easily exceed 100 degrees Fahrenheit during this time. Tomatoes do not do well at temperatures much above 85 F. My tunnel is on a fairly flat site with limited air movement through the tunnel. I advise anyone putting up a new tunnel to place it on a slight slope if possible so that the chimney effect created by the elevation difference can move hot air out of the tunnel.

For high tunnel research reports generated by Michigan State University Extension at SWMREC, go to the SWMREC Annual Reports website and look at the Annual Reports starting in 2005.

For more information on commercial vegetable production, contact Ron Goldy at 269-944-1477 ext. 207.

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