September arrives with a short leash in cold-winter zones. The first frost is roughly six weeks away, and the math on most cool-season crops has already run out. This is not the month for a long seed list — it is the month to transplant the brassicas you started in July and August and to sow radishes, which are fast enough to still make it. Everything else is harvest mode. Act in the first week or the window closes.
Indoors (fresh harvests):
- Microgreens: peas, broccoli, sunflowers, arugula
- Sprouts: alfalfa, broccoli, radish, mung
- Herbs & greens under lights: chives, parsley, mint
Transplants to move outdoors (harden first): Broccoli, cabbage, cauliflower, kale, and kohlrabi started in August should be reaching transplant size now. Get them in the ground in early September — they need every remaining week of growing weather. Harden carefully; mornings are cooling, but afternoons can still be warm.
Crops that can be directly sown outdoors in September: Radish — sow in the first week of September. With a 30-day cycle and a fall factor of 44, radishes are the only reliable direct-sow crop left in cold-winter zones. Order and sow immediately.
Cover crops: Winter rye, winter wheat, hairy vetch, All-Purpose Cover Crop Mix— excellent choices for any beds that are done producing. These establish quickly in cool soil and protect through winter.
Tip: An upstate New York zone 6 can be different from a Santa Fe, New Mexico zone 6. Nothing replaces talking with experienced gardeners in your area and, of course, watching the weather closely.
Use your USDA zone as a guide. Microclimates matter — coastal/urban spots run warmer; high-elevation spots run colder.
