What to Plant in Phoenix in December
December in Phoenix is what the rest of the gardening world envies. While most of the country is under frost or snow, Phoenix gardeners are harvesting fresh lettuce, kale, broccoli, and carrots from their backyard. December is peak cool-season production — and it's also when you start the clock on the spring garden that begins in January.
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What's Harvesting in Phoenix in December
This is the best month in the cool-season garden:
- Lettuce — Full leaves at cut-and-come-again peak. Sweet, crisp, far better than anything from a store in December.
- Kale — Full production. Flavor is actually better after cold temperatures. Harvest outer leaves continuously.
- Spinach — Best flavor of the season in December's cooler temperatures.
- Arugula — Nutty and slightly spicy. Producing from second or third succession now.
- Swiss chard — Producing steadily. More cold-tolerant than spinach.
- Broccoli — Heads forming. October transplants take 90–100 days, so expect them mid-January into February. Cut the main head when it's tight and dark green. Side shoots continue producing for weeks after.
- Cauliflower — Heads forming; harvest before they start to separate or yellow.
- Radishes — If you succession-sowed in November, these are ready now.
- Snap peas — Approaching harvest for October 15 plantings.
- Carrots — First carrots from October plantings are reaching harvest size by late December.
What to Plant in December
Tomato Seeds — Start Indoors Now
Late December is the time to start tomato seeds indoors. Germinate and grow them inside through January and early February. By the time the February 15 outdoor transplanting window opens, your plants will be 6–8 inches tall and ready to go in the ground with a significant size advantage over nursery transplants of the same variety.
Onion Transplants and Sets
Onion sets and transplants go in the ground December 1 through February 1. Buy transplants from a local nursery or plant sets directly in the soil.
Succession Lettuce
If you have empty bed space, sow another round of lettuce seeds. December-sown lettuce harvests in January and February, extending your fresh salad season into the spring transition period.
Line Up Seed Potatoes
Line up certified seed potatoes now for January planting: growing potatoes in Phoenix.
Asparagus Crowns and Artichoke Starts
December is a good month to plant dormant asparagus crowns (the UA Extension window runs November 1 through February 1): growing asparagus in Phoenix. If you sowed artichoke seed in November, the seedlings go out from January 15: growing artichokes in Phoenix.
Frost Awareness in December
December frost depends on where you live. Central Phoenix rarely freezes, but in the East Valley the median first freeze is around December 10. See Phoenix frost dates and frost protection for your area. When NWS Phoenix issues a Freeze Watch or Freeze Warning:
- Cover tender transplants (broccoli, cauliflower, young lettuce) with frost cloth or old bedsheets overnight
- Take sheets and blankets off the next morning once it warms to about 50°F under the cover (UA Extension's guideline). Frost cloth can stay on through a short cold stretch.
- Established kale, spinach, chard, and carrots need no protection — they handle light frost easily
- Any tomato seeds you've just started indoors are safe — they're inside
Frost cloth plus a few hoops is the simplest setup. Both are in the fall and winter picks on the Phoenix gear page.
December Watering
Reduce watering to once or twice per week in December. Cool temperatures dramatically slow evaporation, and overwatering is a more common problem than underwatering in the winter garden. Check soil moisture with a finger test before watering.
Frequently Asked Questions
What can I plant in Phoenix in December?
Onion transplants or sets, succession lettuce, and — most importantly — tomato seeds indoors (late December) for February 15–March 15 transplanting. December is primarily a harvest month for cool-season crops.
What vegetables are ready to harvest in Phoenix in December?
Lettuce, kale, spinach, arugula, Swiss chard, snap peas, radishes from November succession, and early carrots from October plantings reaching harvest size by late December.
Should I start tomato seeds in December in Phoenix?
Yes — start indoors in late December. After 6–8 weeks, plants are 6–8 inches tall and ready for outdoor transplanting from February 15. This gives you a size advantage over nursery transplants and more variety choice.
Does Phoenix get frost in December?
It depends on where you live. Central Phoenix (Sky Harbor) freezes less than once a year on average, but East Valley areas like Mesa and Chandler average about 10 freezing nights a year, mostly in December and January. See Phoenix frost dates for your area. When frost is forecast, cover tender transplants overnight and remove covers in the morning. Cool-season crops like kale and chard handle light frost easily and need no protection.
January Is Right Around the Corner
The Phoenix Planting Calendar PDF covers the full spring and fall season — so you're never guessing what comes next. Download it and keep it in your garden shed.
Get the Planting Calendar — $7 →← November | January → | All Grow Guides