Most varieties of greens do not grow throughout the market season in the Midwest because of the 85-degree-plus weather, which persists for much of July, August and September. High temperatures (and resulting problems with dormancy and rapid drying of soil) result in poor crop establishment, and bitterness and bolting of lettuce. Other leafy greens are severely affected by high insect populations. The ability to extend the greens season through the summer heat would benefit local growers while meeting a consumer need at peak market times. During the summer of 2001, we used shade-covered high tunnels, and lettuce and green cultivars with reported heat tolerance, to attempt to grow high quality greens throughout the summer in the Kansas City area. Trials comparing monthly plantings of lettuce and green cultivars inside shade-covered high tunnels and in adjacent open-field were conducted at three locations from early July through late-September.
Objective One: Test 17 varieties of lettuce and six varieties of Asian greens to determine what varieties and types of greens produce the best under hot summer conditions when shade cloth is used. We tested ten varieties of lettuce and five varieties of Asian greens, over four plantings each in 2001.
Objective Two: Test combinations of white shade cloth, mulch, and floating row covers to reduce soil and air temperatures and to control pests. White shade cloth was used, but not floating row cover.
Objective Three: Determine if the capital investment and extra labor involved in growing under shade cloth is justified by the income potential. Objective Four: To develop a documented, workable and affordable system for growing greens in the Midwestern summer heat that can be used by other growers.