Lettuce Season Extension for Warmer Climates

Commodities

• Vegetables: greens (lettuces)

Practices

• Crop Production: row covers (for season extension), season extension

I am interested in exploring the possibility of extending certain cool season crops into summer by utilizing shade cloths and selecting for heat-tolerant varieties. The study I am proposing would combine both of these specifically in regard to head lettuce. There are more variables to be explored in the future, such as overhead watering and misting systems, different types of mulching, and other crops and varieties (kales and cilantro). While researching squash bugs on our farm, an entomologist and my partner noticed that the squash underneath the Proteknet was growing at a much faster rate than the squash outside of the netting. This could be due to it aiding in respiration and cycling of CO2. If the lettuce grows more quickly under the netting, it could then produce a marketable head more quickly, avoiding some of the adverse effects of warmer temperatures. As a farmer of twenty years myself, I would calculate costs and consider the lowest cost and still most effective means of achieving the results I aspire towards.

In order to learn whether shade cloth can extend the season for lettuce growth from late-June through mid-September in Alabama, a 50-foot bed will be planted every two weeks and covered with a 50% shade cloth. The cloth will hover above the crops, resting on hoops set out every 5 feet. Another 50-foot section of each bed will be planted at the same time but instead have the hoops and Proteknet covering it. A 5-foot space in between the two will be planted, but left uncovered as a control. Because we know from experience that lettuce will not grow well in the southern summer heat without some form of aid, any more than a small control space would be a waste of resources. Beds would be planted at two-week intervals from June 1st through July 15th and then repeated on three other beds beginning August 1st. Three heat-tolerant varieties of lettuce will be trialed; ‘Bergam’s Green’ (green leaf), ‘Cherokee’ (red summer crisp), and ‘Lovelock’ (multicolored). 2- 128 plug flats will be seeded every two weeks beginning on May 1st. Each flat will have equal number
of the three varietals. One month after seeding, one flat will be transplanted and covered with shade, while the other is
transplanted and covered with Proteknet. Succession planting will continue every two weeks for 12 weeks, creating 6 successions, as the temperatures increase. In order to increase chances of success, all transplants will be planted into pre-irrigated soil in three rows with plants 12 inches apart within the rows. The beds will be covered with white plastic mulch in order to lessen weed pressure. Measurements will be taken weekly. The measurements taken will be of the temperature both beneath each shade cloth and beneath each insect barrier, as well as temperature with no cover. Plant growth will also be measured and charted weekly. Observations of physical characteristics such as yellowing of leaves, tip burn, and tendency to bolt will be noted weekly as well. When lettuces are ready to harvest, they will be both counted (heads) and weighed. Marketable, as well as notably unmarketable, data will be collected.