Where summer's sun is most intense, such as the Gulf Coast, Florida, and the desert Southwest, growing tomatoes in summer is difficult. While gardeners elsewhere are enjoying vine-ripened tomatoes in August and September, tomato plants in these hot climates are mostly finished. Adapted varieties, such as 'Heatwave II', have helped expand the growing season for tomatoes in these regions. Now, research from Louisiana State University's Red River Research Station in Bossier City confirms the best hot-weather growing techniques.
The research determined that high soil temperature especially in the top 3 inches of soil is a primary reason that growth and harvests fail in hot weather. To counteract this, horticultural researcher H.Y. Hanna sought techniques to reduce soil temperatures for the plants. Hanna's research demonstrated that deep transplanting, early morning watering, and a reflective white plastic mulch all contributed to higher yields. Combined, these methods increased yields by 20 percent.
Specifically, cover the row or the area around an individual plant with white plastic mulch to reflect the sun's heat. Plant seedlings (after cutting a hole in the plastic) so the rootball is 6 inches deep. (Gradually enlarge the hole in the plastic as the plant grows.) When you water, do it early in the morning (between 6 and 7 a.m.) At that time of day, the plant is more able to absorb water, and the water helps keep the soil temperature down.