September is the turning point in warm-winter zones. The brutal heat of summer is easing, and the long, productive fall and winter season that defines gardening here is beginning to take shape. August brassica transplants are going outside. Short-day onion starts are going out or will be soon. And direct sowing of cool-season crops broadens as soil temperatures fall; this is the month the seed packets you have been holding since August finally go in the ground. Order anything you are missing now; the season does not wait.
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, cauliflower, cabbage, and Brussels sprouts started in August are ready to harden off and move outside as daytime temperatures ease into the upper 80s and below. Watch moisture carefully during establishment; the soil is still warm, and transplants will stress quickly if allowed to dry out.
Short-day onion transplants: Short-day bulbing onions started in August go outside in September and October. These need the full fall and winter season to develop — getting them in the ground now is essential.
Crops that can be directly sown outdoors in September: Spinach, kale, collards, Swiss chard, lettuce, arugula, mustard, pak choi, turnip, radish, carrot, bunching onion, cilantro, dill, corn salad, and beet can all go in this month as conditions allow — earlier in the month for more heat-tolerant crops, later as temperatures continue to fall. For spinach and carrots, pre-germination in a cool spot improves germination if the soil is still warm. In Hawaii and other tropical arias, sow in the cooler microclimates available to you.
Cover crops: Cowpeas and sorghum-sudangrass are still viable early in the month. Transition to crimson clover, field peas, or oats as temperatures cool.
Tip: A Southern California zone 10 can be very different from a Florida zone 10. Consider checking with your state Extension Service office for more specific recommendations and guidelines.
Use your USDA zone as a guide. Microclimates matter — coastal/urban spots run warmer; high-elevation spots run colder.
