Freeze dates by area · What to cover · How to protect plants
Ask "when is the last frost in Phoenix?" and you'll get different answers depending on who you ask and where they live. That's not because anyone has it wrong. Central Phoenix, with all its pavement, barely freezes at all, while parts of Mesa, Chandler and Gilbert get a week or more of freezing nights most winters. Here are the real numbers by area, which crops need protection, and how to cover them.
These are NOAA's official 1991–2020 climate normals for a freeze (32°F or colder), the same dataset the National Weather Service uses. "Median" means the freeze came later (or earlier) than that date in half of the years. The "1 in 10" columns are the safer planning dates.
| Station (area) | Last freeze (median) | 1 in 10 years, later than | First freeze (median) | 1 in 10 years, earlier than | Freeze nights / year |
|---|---|---|---|---|---|
| Sky Harbor (central Phoenix) | Jan 5 | Jan 22 | Jan 3 | Dec 18 | 0.6 |
| Deer Valley (north Phoenix) | Jan 8 | Feb 12 | Dec 25 | Dec 5 | 2.6 |
| South Phoenix | Jan 21 | Feb 20 | Dec 16 | Nov 29 | 8.5 |
| Tempe (ASU) | Feb 13 | Mar 9 | Dec 5 | Nov 18 | 9.7 |
| East Mesa | Feb 1 | Feb 28 | Dec 10 | Nov 22 | 11.1 |
| Chandler Heights (SE Chandler) | Feb 1 | Feb 27 | Dec 11 | Nov 23 | 10.5 |
| Litchfield Park (West Valley) | Jan 7 | Feb 5 | Dec 24 | Dec 6 | 7.1 |
A few things jump out. Sky Harbor freezes so rarely that its "dates" barely mean anything. In most years it doesn't freeze at all. The East Valley stations are a different story, with a median last freeze around February 1 and a 1-in-10 chance of a freeze after the end of February. Gilbert doesn't have its own long-term NOAA station, but it sits between the Tempe, Mesa and Chandler Heights stations, so plan on East Valley numbers.
The spread isn't new. UA Cooperative Extension's frost publication for Maricopa County, using older data, put average first frost anywhere from November 21 in Buckeye to December 12 in central Phoenix, and average last frost from February 7 in central Phoenix to April 3 in Mesa.
In the East Valley, treat late November through February as frost season and keep covers ready. In central Phoenix, the real risk is mostly December and January, and many winters pass without one.
Your yard can run colder or warmer than the nearest station. According to UA Extension, the coldest temperatures come around daybreak, and calm, clear nights are the most dangerous. With no clouds or wind, the heat escapes fast. Cold air also flows downhill like water and pools in low spots. Frost pockets are usually:
Warmer spots include south- and west-facing walls, block walls and patios that soak up sun all day. Extension suggests checking a thermometer in your own yard and comparing it to the forecast, so you learn whether your yard runs a few degrees colder than the official reading.
UA Extension's Master Gardener training sorts warm-season vegetables into two groups:
In a Phoenix winter, the plants that usually need covering are fall tomatoes and peppers still hanging on in December, spring transplants set out in mid-February, basil, young potato shoots, and strawberry blossoms. Young cool-season transplants are also more vulnerable than established plants. Established kale, chard, spinach and carrots handle a light frost fine (see winter greens).
UA Extension says well-watered plants take less frost damage than drought-stressed ones. Firm, bare, moist soil also absorbs more heat during the day and gives it back at night. Water in the morning or early afternoon ahead of a cold night.
Use frost cloth, old sheets or blankets, not plastic. Drape the cover all the way to the ground so it traps the heat coming up from the soil. Ideally, prop it on hoops or stakes so it doesn't rest on the leaves. Extension says a properly applied frost cloth can protect plants down to about 30°F, and some fabrics down to about 20°F.
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Take sheets and blankets off the next morning once it warms up. Extension uses 50°F under the cover as the cue. Left on, they can overheat plants or push them into tender new growth. Frost cloth is lighter. The City of Chandler's desert gardening guide notes it can stay on for a few days, up to about a week, during a cold stretch.
Plants that have been through some cool nights handle cold better. You don't need to keep everything wrapped all winter. Cover on the nights that matter.
Frost-burned leaves look awful, but wait a few days before pulling anything. For perennials and citrus, Extension says not to prune damaged growth until new growth starts in spring.
The National Weather Service office in Phoenix issues a Freeze Watch, normally 2–5 days ahead, when 32°F or colder is expected for the first time in the season or anywhere in the major population areas. A Freeze Warning follows when those temperatures are occurring or imminent. NWS Phoenix's published criteria don't include a separate frost advisory, so the freeze products are the ones to watch.
Have a specific question? The Maricopa County Master Gardeners run a free online Q&A on the 1st Friday and 3rd Saturday of each month (details here).
Want every planting date in one place? My Phoenix Planting Calendar lays out what to plant every month for Phoenix and the East Valley, timed around our frost and heat windows. It's $7, instant PDF download.