Arizona presents a unique challenge for gardeners due to its extreme climate variability. The state’s vast difference in elevation creates two distinct growing environments, meaning planting times are not uniform across the landscape. Success relies entirely on understanding your local microclimate and carefully timing planting to avoid scorching summer heat or damaging winter frost.
Understanding Arizona’s Diverse Climate Zones
Arizona is divided into two primary horticultural regions based on elevation. The Low Desert includes areas generally below 3,500 feet, such as Phoenix and Tucson, and is defined by mild winters and intensely hot summers. The greatest threat to plants here is not frost, which is rare, but sustained temperatures exceeding 100°F, which causes most crops to cease production or perish.
The High Country and Mountain zone encompasses elevations above 4,500 feet, including cities like Flagstaff and Prescott. The primary obstacle here is a severely condensed growing season caused by late spring and early fall frosts. While summers are cooler than the desert, the window for growing tender, warm-season vegetables is much shorter, making timing crucial.
The Low Desert Planting Schedule (Phoenix and Tucson)
The Low Desert’s planting schedule is counter-intuitive, as the mild winter months are used for the main production of cool-season crops. This region utilizes a three-season approach to avoid the heat of June through August. The ideal planting window for most crops occurs in the fall, allowing plants to establish themselves and mature before high temperatures arrive.
Fall Planting (September–October)
The busiest time for the Low Desert gardener begins in early fall, which is the perfect time to sow cool-season crops directly into the soil. Leafy greens like lettuce, spinach, and kale can be planted from seed starting in September, alongside root vegetables such as carrots, radishes, and beets. Brassicas, including broccoli, cabbage, and cauliflower, should be started indoors in August and transplanted into the garden beds in late September or October.
Winter Maintenance and Planting (November–February)
As temperatures dip, the garden moves into its peak production period through the winter months. Hardy crops planted in the fall continue to thrive, and November is an excellent time for a second planting of garlic and onions. While frost is rare, any risk of a late-season freeze should be mitigated with row covers or blankets. This mild period also allows for the planting of perennial herbs like rosemary and thyme.
Spring Planting (February–April)
The spring window is dedicated to warm-season crops that need a head start before the extreme summer heat arrives. Tomatoes and peppers should be started indoors in late December or January and transplanted into the garden between late February and early March. These plants must be well-established by late May, as temperatures over 90°F can cause blossoms to drop without setting fruit. Crops like cucumbers, squash, and melons can be direct-sown from mid-March through April, provided the soil temperature has warmed sufficiently.
The High Country and Mountain Planting Schedule (Flagstaff and Prescott)
Gardening in the higher elevations is governed by the threat of frost, which dictates a much shorter, more traditional growing season. The average last spring frost for Flagstaff is around June 10th, while Prescott sees its last frost around May 6th. This narrow window requires gardeners to begin preparations months before they can safely plant outdoors.
Indoor Seed Starting (March–April)
To compensate for the risk of frost, tender, warm-season crops must be started indoors well in advance. Tomatoes, peppers, eggplants, and annual herbs should be sown indoors six to eight weeks before the expected last frost date, generally beginning in March or early April. This allows seedlings to grow into robust transplants ready to begin flowering and fruiting once moved outside. Starting hardy greens like cabbage and broccoli indoors during this time is also beneficial.
Outdoor Planting (Post-Frost)
The most reliable time to safely move all tender plants outdoors is after the last expected frost date, often in late May or early June. Once the threat of freezing temperatures has passed, direct sowing of quick-maturing crops can commence. These include potatoes, peas, beans, and corn. The cooler summer temperatures are well-suited for cool-season crops, allowing for successive plantings of lettuce, spinach, and radishes throughout the summer.
Autumn Preparation (September)
The growing season concludes abruptly with the first fall frost, which for Flagstaff can occur as early as September 11th. Gardeners must monitor nighttime temperatures closely starting in late August and harvest all remaining warm-season crops before the first freeze. The short window between the last spring frost and the first fall frost emphasizes the need to select crop varieties with shorter “days to maturity.”