Broccoli is a cool-season vegetable, but growing it successfully in Arizona requires precise timing due to the intense heat. High temperatures cause the plant to stop forming the desired head and “bolt,” or flower prematurely. Proper planting must align the heading stage with the mildest temperatures of the year, which varies significantly between the low desert and high mountain regions. Following an accurate planting calendar is the most important factor for success.
Primary Planting Windows for Low Desert
The low desert regions (Phoenix, Tucson, and Yuma) offer two distinct planting windows designed to avoid summer heat. The primary and most reliable season is the fall and winter crop. Start seeds indoors as early as late August or early September to develop transplants ready for the garden.
Move transplants outdoors from late September through October, allowing them to mature during the mild winter months. This timing ensures heads form and are ready for harvest before the hot days of late spring. For a secondary, riskier spring crop, transplants can be set out in January and early February. This schedule aims for a quick harvest before the last frost date, but risks premature bolting if the desert heat arrives early in March or April.
The goal is to cultivate the plant entirely within the cooler period between the extreme summer heat and the spring temperature rise. Broccoli is frost-hardy and can tolerate temperatures down to 28°F, making it an excellent crop for the low desert’s mild winter. Planting successive rounds of transplants every few weeks from September through January can provide a continuous harvest until the weather turns hot.
High Elevation Planting Adjustments
Planting strategies change for high elevation areas (Flagstaff, Prescott, and Payson) which have a much shorter growing season. These regions, generally above 3,000 feet, have later last-frost dates and cooler summer temperatures, allowing for traditional spring planting. The growing season is often only 150 to 220 days long, contrasting sharply with the low desert’s potential.
For a summer-to-fall harvest, set transplants out approximately two to three weeks after the average last spring frost date (mid-May to early June). Start seeds indoors six to eight weeks earlier to have appropriately sized transplants ready. The cooler summer temperatures promote better head formation compared to the struggle against spring heat in the low desert.
A second planting for a late fall harvest is possible in these cooler climates. Select early-maturing varieties and transplant them in mid-to-late summer. This fall crop benefits from the cool, dry weather, but plants must be mature enough to harvest before the first hard freeze of autumn.
Crucial Environmental Factors for Success
The Arizona sun and dry air necessitate specific environmental management, even with perfect timing. Broccoli requires rich, well-draining soil with a slightly acidic to neutral pH (ideally between 6.0 and 7.5). Since the plant is a heavy feeder, incorporate substantial organic matter, such as compost, and side-dress with a nitrogen-based fertilizer two to three times during the growing season for large head development.
Consistent, deep watering is paramount for preventing premature bolting due to drought stress. The dry air causes rapid water loss, so the soil must be kept evenly moist, often requiring 1 to 1.5 inches of water per week. Using drip irrigation and a thick layer of organic mulch helps conserve moisture and stabilize soil temperature.
Broccoli grows best when the air temperature is consistently between 65°F and 75°F. In the low desert, the intense mid-day sun can stress young plants even during the cool season. Applying a 50% shade cloth during the hottest hours mitigates the risk of stress and premature flowering. Sustained exposure to temperatures above 80°F, combined with water stress, triggers the plant to produce small, poor-quality heads (“buttoning”), followed by rapid bolting.