What to Plant in Phoenix in September

Start Brassica Seeds Indoors (September 1–15)

Broccoli and cauliflower take 6–8 weeks from seed to transplant-ready size. Starting them indoors September 1–15 means plants are ready for October 15–31 transplanting — exactly the right timing. This is the only way to grow full-sized broccoli and cauliflower from seed in Phoenix.

How: Use seed starting cells or small pots with seed-starting mix. Keep in air-conditioned conditions or a shaded spot — seeds need under 80°F for good germination. Water lightly and consistently.

Transplant date: When plants have 4–6 true leaves — typically October 15–31.

September Bed Preparation

Remove Summer Crop Debris

Pull out finished summer crops — okra plants, dead sweet potato vines (after harvesting tubers), any remaining basil that's gone to seed. Clean out beds so you're starting fresh for fall.

Amend Soil

Add 2–3 inches of mature compost to beds and work it in lightly. After a summer of heat and dormancy, your soil needs organic matter refreshed. September gives this a month to break down further before you plant.

Check Drip Irrigation

Walk the entire drip system and check: Are all emitters unclogged? Is the timer working correctly? Are any tubing connections loose? Fix everything in September before fall crops are depending on it. A drip failure in a heat spike is much more damaging to established plants than to empty beds.

What You Can Direct Sow in Late September

In the final week of September — once daily highs are consistently below 95°F — you can push slightly and direct sow a small amount:

• Kale (more heat-tolerant than most cool-season crops)
• Swiss chard
• Cilantro

These can handle warmer soil better than lettuce, spinach, or carrots. Germination may be slower and less even than October-planted crops, but you'll get a head start on your fall garden.

September Shopping List

• ☐ Lettuce mix seeds (several varieties)
• ☐ Kale seeds (Dinosaur/Lacinato and Red Russian)
• ☐ Spinach seeds
• ☐ Carrot seeds (Nantes or Danvers types)
• ☐ Snap pea seeds
• ☐ Radish seeds
• ☐ Beet seeds
• ☐ Broccoli/cauliflower transplants (if not starting from seed)
• ☐ Garlic cloves for planting in October–November

Frequently Asked Questions

What can I plant in Phoenix in September?

Start broccoli and cauliflower seeds indoors September 1–15 for October transplanting. Direct sow cool-season crops outdoors starting only in very late September (after the 20th) if temperatures have dropped. For most crops, wait until October 1.

Is September too early to start a fall garden in Phoenix?

For most outdoor planting, yes. The exception is starting brassica seeds indoors in early September. Direct sowing lettuce, carrots, or most fall crops works best starting October 1 when soil is cooler.

What should I do to prepare my garden for fall in September?

Start brassica seeds indoors, top-dress beds with compost, check and repair drip irrigation, remove summer crop debris, buy fall seeds, and plan your bed layout for the fall season.

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