Phoenix, Arizona Frost Dates & Planting Calendar
Phoenix is located in Arizona at an elevation of 1,086 feet. The city falls within USDA plant hardiness zone 9b, where average annual extreme minimum winter temperatures range from 25 to 30 degrees Fahrenheit. With a 322-day growing season, Phoenix gardeners have an extended window for growing vegetables, herbs, and flowers.
Frost Date Summary for Phoenix
Last Spring Frost
January 27
This is the average date of the last freezing temperature (32 degrees F or below) in spring. After this date, it is generally safe to transplant frost-tender seedlings outdoors. In any given year, the actual last frost may occur one to three weeks earlier or later.
First Fall Frost
December 15
This is the average date of the first freezing temperature in autumn. Frost-sensitive crops must be harvested before this date, or protected with row covers and frost blankets. Plan your fall garden so crops mature well before this date.
Growing Season
322 days
The number of frost-free days between the average last spring frost and first fall frost. When choosing crop varieties, compare their "days to maturity" against your growing season length to ensure they have time to produce a harvest.
Hardiness Zone
Zone 9b
USDA hardiness zone based on average annual extreme minimum temperature of 25 degrees F. Perennial plants, trees, and shrubs rated for zone 9b or lower should survive winter here. Learn more about zone 9.
Planting Calendar for Phoenix
These recommended planting dates are calculated from Phoenix's average frost dates. Adjust based on current weather conditions and forecasts.
December 9
Start warm-season seeds (tomatoes, peppers, eggplant) indoors under grow lights approximately seven weeks before the average last frost. This gives transplants time to develop strong root systems before going outside.
February 10
Two weeks after the average last frost date, soil and air temperatures should be warm enough for transplanting hardened-off seedlings. Check the 10-day forecast before committing tender plants to the ground.
October 6
The last practical date to direct-sow fall crops like beans, squash, and quick-maturing greens so they mature before the average first fall frost. Choose fast-maturing varieties for late plantings.
Monthly Gardening Timeline
Below is a general month-by-month overview of garden activities for Phoenix, based on its 322-day growing season and zone 9b climate. Specific tasks depend on your exact crops and gardening style.
| Month | Activity |
|---|---|
| January | Direct sow cool-season crops (peas, lettuce, radishes). Harden off indoor seedlings. |
| February | Transplant warm-season starts after last frost. Direct sow beans, squash, corn. |
| March | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| April | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| May | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| June | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| July | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| August | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| September | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| October | Maintain summer garden: water, weed, fertilize, harvest. Succession plant greens. |
| November | Plant fall crops: broccoli, kale, lettuce. Begin harvesting storage crops. |
| December | Harvest remaining crops before frost. Protect tender plants with row covers. |
What to Grow in Phoenix (Zone 9b)
With 322 frost-free days and minimum winter temperatures around 25 degrees Fahrenheit, Phoenix supports a broad range of edible and ornamental plants. Selecting varieties matched to your season length ensures the best results.
Warm-Season Vegetables
Tomatoes, peppers, eggplant, okra, watermelons, cantaloupes, and sweet potatoes have ample time to produce multiple harvests. Plant early varieties in spring and long-season varieties for peak summer production.
Cool-Season Vegetables
Plant cool-season crops like lettuce, spinach, peas, and radishes in early spring and again in late summer for fall harvest. Broccoli, cauliflower, and cabbage transplants go out in early spring and again in August.
Perennial Edibles & Fruit
A wide range of fruit trees including peaches, plums, figs, and pears grow well. Berry bushes, asparagus, rhubarb, and perennial herbs establish easily in the long growing season.
Zone 9b Details for Phoenix
Temperature Range: 25°F to 30°F average annual extreme minimum
Description: Southern Florida and coastal California; near-tropical
Elevation: Phoenix sits at 1,086 feet, which influences both frost timing and growing conditions. Higher elevations within zone 9b may experience slightly later spring frosts and earlier fall frosts than lower-elevation locations in the same zone.
Frost Protection Tips for Phoenix Gardeners
Even with careful planning around average frost dates, unexpected late spring frosts and early fall frosts can threaten your garden in Phoenix. Having protective materials ready and monitoring weather forecasts closely during the shoulder seasons is essential for preventing crop losses. Here are proven techniques for extending your growing season in zone 9b.
Spring Frost Protection
Keep frost blankets, row cover fabric, or old bed sheets on hand from the time you first transplant until at least two weeks past the average last frost date of January 27. Cover plants in late afternoon when frost is forecast. Jugs of water placed among plants absorb daytime heat and release it at night, raising temperatures by one to two degrees. Wall O' Water protectors allow transplanting up to four weeks early by creating a warm microclimate around individual plants.
Fall Season Extension
As December 15 approaches, covering mature plants with row cover when frost is forecast can extend your harvest by two to six weeks. Cold-tolerant crops like kale, carrots, spinach, and Brussels sprouts actually improve in flavor after light frost, so leave these in the ground and protect them with mulch or low tunnels. Harvesting all remaining tomatoes, peppers, and squash before a hard freeze and ripening them indoors is better than losing them to cold damage.
Other Cities in Arizona
Compare frost dates and growing conditions across Arizona: