Gardening in Arizona during July presents unique challenges and opportunities, defined primarily by intense solar radiation and the arrival of the monsoon season. The extreme heat requires a shift in planting strategy, moving away from most spring crops and focusing on resilient, heat-loving varieties or starting seeds indoors for the fall harvest. Success depends on selecting the right plants and implementing specific techniques to mitigate intense summer temperatures. Specialized knowledge about Arizona’s microclimates and planting schedules is necessary for a productive garden.
Differentiating Arizona’s Planting Zones
Arizona’s vast elevation changes create two distinct gardening zones: the Low Desert and the High Desert/Mountain Zones. The Low Desert, which includes metropolitan areas like Phoenix and Tucson, experiences July temperatures consistently exceeding 100°F, often reaching 115°F, with overnight lows sometimes remaining above 90°F. This environment is classified as USDA Zones 9b to 10b, where the focus in July shifts toward preparing for the fall growing season. The High Desert and Mountain Zones, encompassing regions such as Flagstaff and Prescott, operate in cooler USDA Zones, typically 5b to 7b. Here, July represents the peak of summer production, allowing for the planting of quick-maturing summer crops. The longer growing season in the Low Desert allows for a second chance at heat-tolerant summer vegetables.
Edible Crops to Start Now
For Low Desert gardeners, July is the time to sow seeds for fall crops that require a long growing period. Broccoli, cauliflower, and Brussels sprouts should be started indoors now to mature into transplants ready for the cooler soil of September and October. Starting these seeds indoors protects them from scorching soil temperatures, which can be lethal to young seedlings.
Heat-tolerant summer crops can still be direct-sown outdoors, taking advantage of the increased humidity from the monsoon. Okra is a prime example, thriving in temperatures well above 90°F and producing until the first frost. Other viable direct-sow options include Black Eyed Peas (cowpeas), which are highly drought and heat-resistant, and various types of winter squash like butternut and pumpkin.
Gardeners in the High Desert can direct-sow quick-producing varieties like bush beans and summer squash for a final summer harvest. The cooler zones focus on crops that will mature before the earlier autumn frost. Planting heat-set tomato varieties, such as ‘Roma’ or ‘Heatwave,’ as transplants in the Low Desert can yield a late-season harvest, as they set fruit when night temperatures are high. Monsoon planting also includes corn and melons, which should be planted early in July to ensure maturity.
Herbs and Flowers That Thrive in Summer
July is an excellent time to plant herbs and flowers that tolerate intense heat, providing color and flavor throughout the summer. Basil, particularly the heat-tolerant ‘Thai’ or ‘Sweet’ varieties, can be continuously sown and harvested, though it may require afternoon shade in the Low Desert to prevent wilting. Mediterranean herbs like rosemary, oregano, and thyme are also well-suited for the heat and drought conditions common in Arizona, provided they are established and given deep, infrequent watering.
For vibrant color, several ornamental flowers are perfect for the intense Arizona sun. Zinnias and sunflowers are resilient and can be direct-sown now to provide continuous blooms through the late summer and fall. Vinca (periwinkle) is another popular choice, known for its ability to withstand high temperatures and maintain color when other annuals fail. Native and adapted plants like Baja Fairy Duster and Common Lantana are excellent choices that require less water and maintenance once established.
Protecting New Plants from Extreme Heat
Successfully establishing new plants in July requires protective measures to shield them from the damaging effects of the sun and heat. Shade cloth is a primary tool, with a recommended range of 30% to 50% shade offering sufficient protection for most vegetables and sensitive ornamentals. This covering helps reduce the air and leaf temperature, minimizing the risk of sunscald and heat stress.
Watering must be deep and infrequent to encourage the roots to grow downward, rather than remaining near the surface where the soil dries out quickly. Watering in the early morning is recommended, allowing the plants to hydrate before the intense heat of the day maximizes transpiration. A cycle-and-soak method, where water is applied in short bursts with rest periods, improves absorption and reduces runoff.
Applying a two to three-inch layer of organic mulch, such as straw or wood chips, is essential for regulating soil temperature and retaining moisture. Mulch acts as an insulator, keeping the root zone cooler and reducing evaporation from the soil surface by up to 50%. When planting, aim for the cooler parts of the day, such as the late evening, to give the new plant time to recover from transplant shock before facing the next day’s sun.