When To Plant Seeds In Arizona

Figuring out when to plant seeds in Arizona can feel confusing. The key is understanding our unique climate, which is very different from most gardening guides. Our intense sun, low humidity, and distinct seasons mean your planting schedule is everything. Get it right, and your garden will thrive. Get it wrong, and you’ll battle the heat or frost.

This guide breaks it down simply by region and season. We’ll cover the best times for vegetables, flowers, and herbs so you can plan your garden calendar with confidence.

This is your core calendar. Arizona has three main growing seasons: cool, warm, and monsoon. The timing for each depends heavily on whether you live in the low desert (like Phoenix) or the high country (like Flagstaff).

Low Desert Planting (Phoenix, Tucson, Yuma)

The low desert has long, hot summers and mild winters. Frost is rare but possible. Here’s how to plan:

Cool Season (Oct – Feb): Plant seeds from October through February. This is prime time for many crops. The goal is to harvest before the late spring heat arrives.
Warm Season (Mar – May): Plant heat-lovers from mid-February through April. These need to be established before the extreme summer heat.
Monsoon Season (Jul – Aug): A second chance for warm-season crops. Plant in July to use the summer rains and slightly cooler nighttime temps.

High Country Planting (Flagstaff, Prescott, Payson)

These areas have cold winters and a much shorter frost-free window. The summer is mild and perfect for growing.

Cool Season (Apr – Jun & Aug – Sep): You have two shorter cool seasons. Plant as soon as soil is workable in spring, and again in late summer for a fall harvest.
Warm Season (Jun – Jul): The main planting happens after the last frost, usually in May or June. You must use fast-maturing varieties.

Vegetable Seed Planting Guide

Here’s a practical list for the low desert. Adjust by a few weeks earlier for the high country spring/summer, and later for the fall.

Cool Season Vegetables

These tolerate frost and prefer temperatures below 75°F. Direct sow seeds into your garden beds.

Plant in October/November: Beets, carrots, kale, lettuce, peas, radishes, spinach, Swiss chard.
Tip: For continuous harvest, sow lettuce and radish seeds every 2-3 weeks (succession planting).

Warm Season Vegetables

These need warm soil and no frost. They often struggle in peak July heat.

Plant in March/April: Beans, corn, cucumbers, melons, peppers, squash, tomatoes.
Tip: Start tomato and pepper seeds indoors in January to get strong seedlings ready for March planting.

Monsoon Season Vegetables

Replant heat-lovers that can benefit from the rainy season.

Plant in July: Beans, corn, cucumbers, summer squash, pumpkins (for Halloween).

Flower Seed Planting Guide

Flowers also follow the cool/warm pattern. Always check seed packets for “days to bloom” to ensure they beat the season change.

Cool Season Flowers

These add color to your winter and spring garden.

Plant in November/December: Calendula, larkspur, pansies, poppies, snapdragons, sweet peas.
Sweet peas need a trellis and are worth the effort for their fragrance.

Warm Season Flowers

These are the sun-loving, drought-tolerant champions.

Plant in April: Cosmos, marigolds, sunflowers, zinnias, gomphrena.
Zinnias are incredibly easy and provide excellent cut flowers all summer long if you keep them picked.

Step-by-Step: Preparing and Planting Your Seeds

Just throwing seeds in the ground isn’t enough in Arizona. Follow these steps for better success.

Amend the Soil: Our native soil is often hard clay or sand. Mix in 3-4 inches of compost before planting. This improves drainage and provides nutrients.
Check Soil Temperature: Use a soil thermometer. Cool-season crops germinate in 55-70°F soil. Warm-season crops need at least 70°F.
Plant at the Right Depth: A general rule is to plant a seed twice as deep as it is wide. Tiny seeds (like lettuce) just need a light sprinkle of soil on top.
Water Gently: Use a fine mist or soaker hose to water seeds in. You must keep the top inch of soil consistently moist (not soggy) until seeds sprout. This can mean watering twice a day in our dry air.
Provide Shade for Sprouts: For seeds planted in late winter for spring harvest, use a 30-50% shade cloth to protect tender seedlings from intense afternoon sun.

Common Arizona Gardening Challenges & Solutions

Every region has its hurdles. Here’s how to get past Arizona’s biggest ones.

Intense Sun and Heat

Problem: Seeds dry out too fast; seedlings get sunburned.
Solution: Use shade cloth during establishment. Mulch heavily with straw or wood chips to retain soil moisture and cool roots.

Low Humidity and Dry Winds

Problem: Rapid moisture loss from soil and plants.
Solution: Water in the early morning. Consider windbreaks like lattice or taller plants on the windward side of your garden.

Alkaline Soil and Hard Water

Problem: High pH can lock up nutrients, causing yellow leaves.
Solution: Regularly add compost and use acid-loving fertilizers or soil sulfur for plants like tomatoes and peppers. A soil test is very helpful here.

FAQ: Planting Seeds in Arizona

What month do you start seeds in Arizona?

It depends on the plant! For cool-season crops, start in October. For warm-season crops, start in February or March. Always refer to a local planting calendar for the most acurate dates.

Can you plant seeds year-round in Arizona?

In the low desert, you can plant something almost every month, but there is a “dead zone” in June and sometimes late December for certain plants. The high country has a more restricted, traditional summer growing season.

How do you germinate seeds in hot weather?

Pre-cool the soil by watering in the evening. Plant seeds slightly deeper than usual, and cover the area with a damp burlap sack or board for 2-3 days to keep it cool and moist. Check daily for sprouts and remove the cover immediately when they appear.

What are the easiest vegetables to grow from seed in Arizona?

For beginners: radishes, green beans, Swiss chard, zucchini, and black-eyed peas are all tough and reliable in our climate. They have good germination rates and can handle some stress.

Is it better to start seeds indoors or direct sow in Arizona?

For tomatoes, peppers, and eggplants, starting indoors gives them a head start. For root crops (carrots, radishes) and plants that dislike transplanting (beans, squash), direct sowing is always best. Just be prepared to protect the young seedlings.

Gardening in Arizona is a rewarding adventure once you sync with the seasons. By planting your seeds at the correct time and providing a little extra care during germination, you’ll be harvesting your own fresh produce and enjoying vibrant flowers. Keep a simple garden journal each year noting what worked and when you planted—it will be your most valuable tool for seasons to come.