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. It's the most reliable 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

Frequently Asked Questions

What can I plant in Phoenix in September?

Start broccoli and cauliflower seeds indoors September 1–15 for October 15–31 transplanting. Once highs stay below 95°F in late September, you can direct sow kale, chard, and cilantro. For most other crops, October is the top pick, though the UA Extension calendar allows September sowing for many of them.

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

Not if the heat has broken. Early September is usually too hot for good outdoor germination, so use it to start brassica seeds indoors and prep beds. The UA Extension calendar lists September sowing for many cool-season crops, but October is still the top pick 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.

← August  |  October →  |  All Grow Guides