Seed Starting Vegetables in September

September marks the true turning point in the vegetable garden. As days shorten and nights cool, the focus shifts away from heat-loving summer crops and toward the cool-season vegetables that thrive in fall and winter. This is the month to reset beds, sow greens and roots, and think ahead about frost protection and season extension. What you plant now—and how you protect it—will determine how productive your garden remains through autumn and into winter.

Table of Contents

Zone-by-Zone Seed-Starting Guide for September

Listed by USDA Plant Hardiness Zones, warmest zones first:

Zone 11

(Where the annual low temperatures stay above 40°F / 4°C.)

Begin the main cool-season planting season.
Direct-sow lettuce, spinach, arugula, mustard, and Asian greens.
Sow carrots, beets, radishes, turnips, and scallions.
Plant broccoli, cabbage, cauliflower, and kale transplants.
Continue sowing herbs such as cilantro, dill, and parsley.
Remove declining summer crops.
Mulch beds lightly to moderate soil temperature.
Water consistently for even germination.

Zone 10

(Where the annual low temperatures can reach 30°F / -1°C.)

Transition fully from summer to fall crops.
Direct-sow leafy greens and root crops.
Plant brassica transplants for winter harvest.
Continue sowing cilantro, dill, and parsley.
Sow peas late in the month in mild areas.
Remove remaining summer crops.
Mulch beds to conserve moisture.
Monitor irrigation as days shorten.

Zone 9

(Where the annual low temperatures can reach 20°F / -7°C.)

Direct-sow lettuce, spinach, arugula, and mustard.
Sow carrots, beets, radishes, turnips, and scallions.
Plant broccoli, cabbage, cauliflower, and kale transplants.
Begin sowing peas mid- to late-month.
Remove spent warm-season crops.
Use row cover to protect seedlings from heat or pests.
Water deeply and regularly.

Zone 8

(Where the annual low temperatures can reach 10°F / -12°C.)

Direct-sow cool-season greens and root crops.
Sow spinach, lettuce, Asian greens, and chard.
Plant fall brassica transplants early in the month.
Begin sowing peas.
Remove remaining summer crops.
Mulch beds to regulate soil moisture.
Prepare frost protection for later in the season.

Zone 7

(Where the annual low temperatures can reach 0°F / -18°C.)

Focus on cool-season planting.
Direct-sow lettuce, spinach, arugula, mustard, and radishes.
Sow carrots, beets, and turnips early in the month.
Transplant broccoli, cabbage, kale, and cauliflower early.
Begin sowing peas in early September.
Install row covers for frost protection.
Remove spent summer crops.

Zone 6

(Where the annual low temperatures can reach -10°F / -23°C.)

Direct-sow fast-maturing greens and root crops early in the month.
Sow spinach, lettuce, arugula, radishes, and turnips.
Transplant hardy brassicas early in September.
Avoid late sowings after mid-month.
Use row covers to protect young plants.
Mulch beds lightly.
Monitor overnight temperatures closely.

Zone 5

(Where the annual low temperatures can reach -20°F / -29°C.)

Limit planting to quick-maturing crops.
Direct-sow spinach, leaf lettuce, radishes, and arugula early in the month.
Transplant hardy greens if already started.
Use low tunnels or row cover immediately.
Remove spent summer crops.
Mulch beds to protect soil.
Plan for early frost.

Zone 4

(Where the annual low temperatures can reach -30°F / -34°C.)

Focus on season extension rather than new plantings.
Direct-sow spinach and radishes early in the month only.
Transplant hardy greens if already established.
Use row cover or cold frames.
Remove remaining summer crops.
Prepare beds for winter protection.
Monitor weather daily.

Zone 3

(Where the annual low temperatures can reach -40°F / -40°C.)

Avoid new sowings except very fast crops early in the month.
Harvest and protect existing crops.
Use cold frames or heavy row cover.
Remove spent plants and add mulch.
Prepare beds for winter.
Focus on extending harvests rather than new plantings.

Fall Transition: Looking Ahead

As September unfolds, gardening becomes more about timing and protection than speed. Some crops are finishing, others are just getting started, and your job is to help the garden make that transition smoothly. Clear spent summer plants, keep young seedlings evenly watered, and begin using row covers, cold frames, or hoop houses as nights cool. With thoughtful planting and early protection, September sets the stage for steady harvests well beyond the first frost.