August is the time to start the fall garden in warm-winter zones, even though the heat makes it hard to believe. With no meaningful first frost, the timing here is driven by when conditions become favorable for cool-season crops; typically late October into November, and working backward from there. Cauliflower, cabbage, broccoli, and Brussels sprouts all need 8 to 10 weeks of indoor growing before they are ready to transplant, which puts their indoor start dates squarely in August. Short-day bulbing onions also go indoors this month for the long production season ahead. The fall harvest that defines gardening in these zones depends on what gets started now.
Indoors (fresh harvests):
- Microgreens: peas, broccoli, sunflowers, arugula
- Sprouts: alfalfa, broccoli, radish, mung
- Herbs & greens under lights: chives, parsley, mint
Start indoors now for fall transplant:Broccoli, cauliflower, cabbage, Brussels sprouts. These need 8–10 weeks indoors before they're ready to set outside — starts made in August will go out in October as temperatures ease.
Start indoors now — long-season crops: Short-day bulbing onions. These need the longest lead time of any fall crop; starting them in August gives them the weeks they need before transplanting in September and October.
Crops that can be directly sown outdoors in August: Parsnip — use the pre-germination technique. Germinate seeds indoors in a cool location on a damp paper towel and move them to the garden before the radicle extends. Parsnip's long growing season makes the extra step worthwhile. In Hawaii and other tropical areas, heat-tolerant crops continue as in July.
Cover crops: Sunn hemp, cowpeas, sorghum-sudangrass — keep the soil covered through the remaining heat.
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.
