Growing tomatoes successfully in Arizona requires adapting traditional methods to the region’s intense heat and arid conditions. The desert environment necessitates abandoning the single, long summer growing season common elsewhere. Instead, gardeners must utilize specific seasonal windows, select specialized varieties, and implement physical protection techniques. This approach ensures plants thrive during mild periods and survive the intense solar radiation and high temperatures that define Arizona gardening.
Understanding Arizona’s Dual Growing Seasons
Gardeners in Arizona, particularly in the low desert areas like Phoenix and Tucson, must operate within two distinct, short growing seasons to successfully harvest tomatoes. The traditional summer period is too hot for most varieties to set fruit, necessitating spring and fall planting windows.
Spring Season
The spring season is a race against the intense heat of late May and June. Plants are typically transplanted outdoors around mid-February to mid-March, after the last threat of frost has passed in the low desert regions. The goal is to establish the plants and allow them to flower and set fruit before daytime temperatures consistently climb above 90 degrees Fahrenheit.
Fall Season
The second growing opportunity occurs in the fall, initiated by planting seedlings in mid-July through August once the worst of the summer heat has passed. This timing allows the plants to mature and produce fruit as the cooler autumn weather arrives, often yielding until the first winter frost, typically in late November. Mid-summer is a high-risk time for tomatoes, as temperatures exceeding 90°F severely reduce pollen viability, causing flower blossoms to drop without setting fruit.
Choosing the Right Tomato Varieties for Desert Climates
Selecting the correct tomato variety is the first specialized step in desert gardening, focusing on genetics that can withstand high temperatures. Most common varieties cease producing viable pollen when air temperatures rise above 90°F, a condition known as blossom drop. Arizona growers must seek out varieties with a “heat set” capability, meaning they can still flower and form fruit even when temperatures are elevated.
Smaller-fruited types, such as cherry and grape tomatoes, generally exhibit higher heat tolerance and are easier to grow in this climate. Specific varieties known to perform well in the desert include Sun Gold, Sweet 100, and Punta Banda. For those seeking larger fruit, hybrid varieties like ‘Heatmaster,’ ‘Solar Fire,’ ‘Phoenix,’ and ‘Celebrity’ are recommended for their resistance to heat stress.
The plant’s growth habit is also a factor. Determinate varieties are frequently favored for the spring season because they grow to a specific height and produce fruit in a concentrated period. This allows for a quick harvest before the severe summer heat arrives. Indeterminate, or vining, varieties can be used for the spring crop and then pruned heavily in the summer to encourage a second flush of growth and fruit production in the cooler fall season.
Techniques for Combating Extreme Heat and Sun
Successfully navigating the Arizona climate requires physically modifying the environment around the tomato plants to mitigate intense sun and heat.
Shade and Protection
The use of shade cloth is necessary when ambient temperatures approach or exceed 90°F to prevent the plant’s delicate foliage and fruit from burning. A shade cloth with a density between 30 and 50 percent is ideal, as it filters out the harshest rays while still allowing enough sunlight for photosynthesis and fruit development. The shade structure should protect plants during the hottest hours of the afternoon, lowering the air temperature and preventing sunscald on ripening fruit.
Watering and Mulching
The intense solar radiation quickly dries out soil, making consistent, deep watering techniques crucial for plant survival and fruit quality. Watering should be deep and thorough to encourage a robust root system, and frequency must increase significantly during extreme heat. Maintaining consistent soil moisture also helps prevent common issues like blossom end rot, which is often exacerbated by inconsistent watering.
To regulate soil temperature and conserve moisture, a heavy layer of organic mulch is essential. Applying two to three inches of organic materials like straw, wood chips, or shredded leaves helps insulate the soil, keeping the root zone cooler and significantly reducing water evaporation.
Soil Amendments
The native desert soil often lacks organic matter and benefits greatly from amendments to improve its water-holding capacity. Incorporating compost, worm castings, and other organic material into the planting area or raised beds creates a nutrient-rich and more retentive soil structure. This improved soil environment, combined with shading and proper watering, forms the foundation for a successful tomato harvest in the challenging Arizona desert.