Lettuce is a cool-weather crop, making successful cultivation in Arizona challenging due to high temperatures. Precise timing is required to align the growing period with the state’s mild winter and early spring months. Because Arizona is geographically diverse, the ideal planting window changes dramatically based on elevation and local climate. Determining when to plant depends entirely on understanding your specific region to avoid extreme heat that prematurely ends the harvest.
Understanding Arizona’s Growing Zones
Arizona’s vast landscape is divided into distinct climate regions that govern all gardening activity. These zones are primarily determined by elevation, which dictates average temperature extremes and the length of the growing season. The two main categories are the Low Desert and High Elevation zones, each requiring a fundamentally different approach to growing lettuce.
The Low Desert, including metropolitan areas like Phoenix and Tucson, sits below 2,500 feet and features mild, frost-free winters and intense, triple-digit summers. This environment necessitates planting in the fall to ensure a long cool-season harvest before spring heat arrives. Conversely, High Elevation regions, such as Flagstaff and Prescott (4,500 feet and above), have short growing seasons defined by late spring frosts and early fall freezes.
Low Desert Planting Calendar (Fall and Spring)
The Low Desert provides an extended cool-weather season, allowing for lettuce harvest throughout the winter. The primary planting window begins in the fall, which is the optimal time for establishing plants for a continuous harvest. Gardeners should sow seeds or plant transplants starting in September and continue succession planting through November.
This timing allows lettuce to develop during the mild temperatures of late autumn and winter. Succession planting can continue into January and February, ensuring a steady supply until temperatures climb. Planting small batches every few weeks prevents all heads from maturing simultaneously.
The season ends when the plant bolts, which is its response to rising temperatures and longer daylight hours. When the weather warms significantly, typically in late March or early April, the lettuce plant rapidly sends up a flower stalk, making the leaves bitter. A brief, secondary spring planting is possible in late February or early March, but only quick-maturing varieties should be used to ensure harvest before the heat causes bolting.
High Elevation Planting Calendar (Spring and Summer)
High-elevation regions, such as Payson and the Colorado Plateau, require a condensed planting schedule due to the short window between frosts. The lettuce planting season shifts entirely to the spring and summer months, contrasting sharply with the Low Desert schedule. The primary concern here is frost damage, which can occur as late as May.
Cool-season crops like lettuce are best started indoors several weeks before the last expected spring frost date, or direct-sown outdoors once the soil is workable. The main planting period usually begins in May, after the danger of a hard freeze has passed. This timing allows the lettuce to thrive during the mild, temperate summer days characteristic of mountain climates.
Gardeners can continue sowing seeds throughout the summer for a continuous harvest until the first hard frost arrives, typically in October. Since summer heat is less intense at these elevations, lettuce remains productive much longer than in the desert. Succession planting every few weeks from May through mid-summer maximizes the yield from this shorter growing window.
Selecting Lettuce Varieties Built for Heat
Selecting the right cultivar is crucial for maximizing lettuce success in Arizona, especially in the Low Desert. Heat-tolerant varieties are genetically predisposed to resist bolting and bitterness longer than standard types. The most successful options are generally found within the Romaine and Looseleaf groups, which handle sun exposure better than the tightly wrapped Crisphead varieties like Iceberg.
Romaine lettuce, including popular cultivars like ‘Parris Island Cos’ and ‘Jericho,’ is known for its ability to withstand higher temperatures before bolting. Looseleaf types, such as ‘Black Seeded Simpson’ and ‘Red Sails,’ are also excellent choices. They can be harvested using the “cut-and-come-again” method, which involves picking only the outer leaves. This technique reduces stress on the plant and encourages continued production, allowing for a longer season even as temperatures fluctuate.