What to Plant in Phoenix in August
August is still fully summer in Phoenix — 100°F+ days are normal through the end of the month. It's not time to plant cool-season crops yet. But August is the month to start preparing for October, which is one of the most important planting windows of the year. Get your beds and your brassica starts ready now.
Start Brassica Seeds Indoors (Late August)
Broccoli and cauliflower can't be direct-sown in Phoenix — by the time soil temperatures drop enough for outdoor germination in October, transplants started in August will already be 6 weeks old and ready to go in the ground. This is how you get larger, more productive brassica plants.
Start seeds indoors: August 20–31
Transplant outdoors: October 15–31 when they have 4–6 true leaves
Use a seed starting mix in small cells or pots. Keep them indoors (air conditioning works great) or in a shaded outdoor area. They need cool temperatures to germinate — no more than 80°F.
Outdoor August Tasks (Not Planting)
Refresh Bed Soil
Top-dress resting beds with 2–3 inches of mature compost. By the time October arrives, it will have partially broken down and integrated into the soil. Don't dig it in now — let summer heat and occasional monsoon rain work it in naturally.
Check and Repair Drip Irrigation
Walk your drip system and check for clogged emitters, broken tubing, or loose connections — monsoon wind and root growth can displace lines over summer. Fix now while plants aren't in the ground, before you need the system in October.
Order Fall Seeds
Summer is the ideal time to order fall garden seeds. Availability of lettuce, kale, spinach, carrot, and pea varieties is best in late summer. Don't wait until September — popular varieties sell out.
Still Growing in August
- Okra — Still producing well into August. Continue harvesting daily.
- Eggplant — Hanging on. Water daily and maintain mulch.
- Sweet potato vines — Growing and developing tubers for fall harvest.
- Basil — Monsoon humidity may cause fungal issues on basil. Trim off any blackened stems and ensure good air circulation.
The Fall Countdown
From late August, the fall garden is just about 6 weeks away. Use this time wisely: start your brassica seeds, refresh your soil, fix your drip, and order your seeds. When October 1 arrives, you want to be ready to plant immediately — the fall window is best used in its entirety.
Frequently Asked Questions
What can I plant in Phoenix in August?
Start broccoli and cauliflower seeds indoors in late August for October transplanting. Outdoors, it's still too hot for cool-season crops. Continue maintaining heat-tolerant crops already growing — okra, eggplant, sweet potatoes.
Can I plant fall vegetables in August in Phoenix?
Not outdoors — still too hot. The exception is starting broccoli and cauliflower seeds indoors in late August so they're ready for October transplanting. Direct sowing lettuce, kale, or carrots outdoors in August will fail due to heat.
How do I prepare my raised beds for fall planting?
Top-dress resting beds with 2–3 inches of mature compost to break down through September. Remove summer crop debris, check and repair drip irrigation, and clear any weed growth. Have beds ready to plant the moment October arrives.
Get the Full Fall Season Timeline
The Phoenix Planting Calendar PDF maps out every fall crop with exact sow and transplant dates for the greater Phoenix area.
Get the Planting Calendar — $7 →← July | September → | All Grow Guides