Fall / Winter Beginner 📍 Phoenix / East Valley, AZ

What to Plant in Phoenix in December

Q: What can I plant in Phoenix in December?

In December you can plant onion sets or transplants, a third succession of lettuce and salad greens, and garlic (if you haven't already). Indoors, start tomato seeds in December for January transplanting — December 1–15 gives you 6–8 weeks before the January 15 outdoor planting window opens.

Q: What vegetables are ready to harvest in Phoenix in December?

October-planted crops are in full production in December: lettuce (cut-and-come-again at peak), kale (full leaves), spinach, arugula, Swiss chard, broccoli heads (first harvest November–December), cauliflower, and radishes from a November succession. Carrots planted in October are reaching harvest size by late December.

Q: Should I start tomato seeds in December in Phoenix?

Yes, if you want large, vigorous transplants for January. Start tomato seeds indoors December 1–15. After 6–8 weeks of indoor growing time, plants are 6–8 inches tall and ready for outdoor transplanting after January 15. This gives you a head start over buying nursery transplants and access to more variety choices.

Q: Does Phoenix get frost in December?

Occasionally. Phoenix averages 1–3 frost nights per year, with most occurring in December and January. Frost is not guaranteed or even likely in any given year, but it happens. When frost is forecast, cover established transplants with frost cloth, old sheets, or cardboard overnight. Remove coverings in the morning once temperatures rise above 40°F. Cool-season crops like kale and chard handle light frost easily.

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.

SeasonWinter Cool Season

Avg. High65–70°F

Avg. Low43–48°F

Frost RiskOccasional — 1–2 nights this month

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 ready to harvest in December from October transplants. 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

December 1–15 is the ideal time to start tomato seeds indoors. Germinate and grow them inside through the rest of December and January. By the time the January 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

Onions are happy going in the ground December through January. 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.

Frost Awareness in December

Phoenix occasionally gets frost in December. Most years, none occurs — but be aware. When a frost is forecast (NWS Phoenix will issue frost advisories):

Cover tender transplants (broccoli, cauliflower, young lettuce) with frost cloth or old bedsheets overnight
Remove coverings the morning after once temperature rises above 40°F
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

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 (December 1–15) for January 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, broccoli heads, cauliflower, 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 December 1–15. After 6–8 weeks, plants are 6–8 inches tall and ready for outdoor transplanting after January 15. This gives you a size advantage over nursery transplants and more variety choice.

Does Phoenix get frost in December?

Occasionally — 1–2 nights in some years. 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 →

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