September Seed Planting Guide

In the Phoenix and San Tan Valley low desert, September is when the garden calendar flips. Summer heat is still hanging around, but day length and overnight lows start shifting in our favor. This is when I get cool-season seeds into trays and beds so we are eating from the garden through winter.

I treat early September carefully because soil can still be uncomfortably hot for tender germinating roots. Late September is usually kinder for peas and some direct-sown crops. Timing within the month matters almost as much as which seeds you choose.

What I sow in September

• Broccoli, cabbage, and cauliflower for fall and winter harvests.

• Lettuce and spinach for quick cool-season salads.

• Radish, carrots, and beets for root crops that love our mild winters.

• Cilantro and dill, which bolt fast in heat but thrive as temperatures ease.

• Peas toward the end of the month once nights cool a bit more.

Hot soil tips and indoor starts

If your beds still feel like a skillet, start brassicas and lettuce indoors or in a shaded spot and transplant later. Direct sow radishes, carrots, and beets into moist soil, then mulch lightly and water consistently so seeds do not cook or crust over. I often shade new seed beds with light cloth for the first week or two.

Keep seed trays out of harsh afternoon sun. Warm mornings help germination, but blazing midday light can dry media in hours. Check moisture twice a day until seedlings are up. Once they have true leaves, harden them gradually before they go into the garden.

September seed planting is one of my favorite jobs of the year because it feels like a fresh start after summer. Pick your crops, respect the residual heat, and get those cool-season seeds moving. Your winter garden depends on the work you do now.