September is the month most American gardeners stop sowing. The tomatoes are winding down, the squash has powdery mildew, the beds look tired, and putting seeds in the ground feels like something that belongs to spring.
For a good deal of the country that instinct is wrong by about six weeks. There are vegetables that grow better sown in September than at any other point in the year, there are crops you can only sow now if you want them at all, and there are beds that could be producing salad in November sitting empty because nobody thought to fill them.
But this is also the month where honesty matters more than enthusiasm. In Minnesota in mid-September you have four weeks before hard frost and there is genuinely very little worth sowing outdoors. In Georgia you have ten weeks and most of the fall garden is still ahead of you. Any article that gives every American gardener the same September list is lying to about half of them.
So this one splits three ways: what you can still sow outdoors and harvest this year, what needs protection to be worth attempting, and what you sow in September for next spring rather than for this autumn. That third category is the one almost nobody covers, and it is where September earns its place.
First: work out how much time you actually have
Everything below depends on this number, so it is worth two minutes.
Find your first frost date. Your county extension service will have it, as will the Old Farmer's Almanac. It is the average date of your first killing frost and it is the single number that decides what September is for in your garden.
Approximate first frost by zone:
- Zone 3: September 1 to 15
- Zone 4: September 15 to October 1
- Zone 5: October 1 to 15
- Zone 6: October 15 to November 1
- Zone 7: November 1 to 15
- Zone 8: November 15 to December 1
- Zone 9: December, if at all
- Zone 10 and warmer: no reliable frost
Now subtract. Count the days from today to that date, then take off two weeks. Growth slows substantially through October as daylength drops, so a crop rated at 40 days in June will take closer to 50 sown in September. That adjusted number is your actual working window.
What that means in practice:
Zones 3 and 4 in mid-September have roughly zero to three weeks. Outdoor sowing for this year is essentially over. Your September is about protection, and about sowing for spring.
Zone 5 has about three to five weeks. Fast salad leaves only, and protection extends that meaningfully.
Zone 6 has five to seven weeks. Most of the quick list below works.
Zone 7 has seven to nine weeks. Everything on the quick list, plus roots.
Zones 8 and 9 have nine to twelve weeks or more. September is a main sowing month, not a last chance.
A word on frost tolerance, because it changes the maths. Several crops on this list are not killed by frost. Kale, spinach, mache, and winter radishes all survive well below freezing and some improve after it. For those, first frost is not a deadline at all, and your real limit is when the ground freezes hard or when light gets too low for growth, typically late November in the north.
The 12 to sow in September
Organized by how much time each one needs, so you can stop reading at whatever point your window runs out.
The fast ones: 25 to 35 days
Viable almost everywhere in early September, and the only outdoor options left in cold zones.
1. Radishes. The fastest thing in the garden. 'French Breakfast', 'Cherry Belle', 'Sparkler'. Sow every ten days through September for a continuous run. They germinate in cooling soil far more reliably than in August heat, and September radishes are noticeably better than summer ones because they grow steadily rather than bolting.
Sow half an inch deep, thin to an inch apart. Crowded radishes make leaves and no root.
2. Arugula. Baby leaves in 25 days, mature in 40. Better in autumn than any other season because cool weather removes the harsh peppery bite that summer arugula develops. 'Astro' is fast, 'Sylvetta' is slower and more strongly flavored.
Direct sow only. It resents transplanting. Cut the outer leaves and it keeps producing for weeks.
3. Asian greens. Mizuna, tatsoi, pak choi, mibuna, Tokyo bekana. This family is the most underused group of crops in the American autumn garden. All of them are fast, all of them prefer cool weather to warm, and tatsoi in particular gets sweeter after frost.
'Joi Choi' for pak choi, 'Tatsoi' for the rosette type, 'Mizuna' for feathery salad leaves. Sow shallow, thin to four inches for baby crops, six to eight for full size.
4. Spinach. September is arguably the best spinach sowing of the year. It germinates poorly in warm soil, which is why August sowings often fail, and September soil is exactly what it wants. 'Bloomsdale Long Standing', 'Giant Winter', 'Space'.
It also tolerates hard frost, so in zones 6 and warmer a September sowing can be picked into December. In colder zones a late September sowing that gets small before winter will sit dormant and give you the earliest crop of next spring, which is the single best reason to sow spinach this month.
5. Lettuce. Loose-leaf and baby-leaf types only at this point. Head lettuce needs more time than most of the country has. 'Salad Bowl', 'Black Seeded Simpson', 'Winter Density', 'Marvel of Four Seasons'.
Cut-and-come-again is the approach that makes sense now. Sow thickly in a band rather than spacing individual plants, and cut across the whole patch with scissors at three inches.
6. Mustard greens. 'Red Giant' is worth growing for looks alone, deep purple-red leaves that hold color into cold weather. Fast, tolerant of frost, and the flavor mellows considerably as temperatures drop.
The middle group: 40 to 55 days
Zone 6 and warmer, sown in the first half of September.
7. Turnips. Both roots and greens, from one sowing. 'Hakurei' is the one to grow if you have not tried Japanese salad turnips, mild and sweet enough to eat raw. 'Purple Top White Globe' for a traditional storing turnip.
Direct sow, thin to four inches. Harvest at golf ball size for the best texture. Larger turnips get woody and hot.
8. Winter radishes. Different plants from spring radishes despite the name. Daikon, 'Watermelon', 'Black Spanish', 'China Rose'. They take 50 to 60 days, get considerably larger, and store for months in a cool place.
Thin to six inches, which feels generous and is not. Daikon in particular needs room and loose soil to go down straight.
9. Kohlrabi. The most overlooked brassica in America. 'Early White Vienna' matures in about 55 days, and the bulb sits above ground so you can watch it swell. Mild, crisp, good raw or roasted.
Harvest at two to three inches across. Bigger than that and it turns woody.
10. Kale. Sown now, kale gives you leaves through autumn, survives winter in most zones, and comes back into growth in early spring for a second season. 'Lacinato', 'Red Russian', 'Winterbor'.
Frost genuinely improves it. The plant converts starch to sugar as protection against freezing, so kale picked after a hard frost is sweeter than kale picked in October. Transplants establish faster than direct sowing if you can find them at this point in the season.
11. Beets. Tight in zone 6, comfortable in zone 7 and warmer. 'Detroit Dark Red', 'Cylindra', 'Bull's Blood' for the leaves as well as the roots.
Beet seed is actually a cluster of seeds, so thin to three or four inches and eat the thinnings as baby greens rather than composting them.
12. Carrots. Zone 7 and warmer only for a fall crop, and choose early varieties. 'Amsterdam Forcing', 'Nantes', 'Napoli'. Sown now they mature in cool weather, which produces sweeter carrots than summer growing.
Germination is slow, ten to twenty days, and needs consistent moisture. Cover the seeded row with burlap or a board until you see green.
What not to sow in September
Being direct about this saves people wasted seed.
Anything in the squash family. Cucumbers, zucchini, summer squash, melons, pumpkins. All need warmth and 50 to 90 days. Not happening anywhere outside zone 10.
Tomatoes, peppers, eggplant. Same problem, worse. Even in Florida these want spring sowing for a fall crop, not September.
Beans and corn. Warm soil crops with no frost tolerance. The window closed in July.
Brussels sprouts, cabbage, cauliflower. Long-season brassicas needing 80 to 100 days. September sowing means a spring harvest at best, and in most zones it means a plant that sits through winter and bolts in April without heading.
Onions from seed. Wrong timing. Onions want either late winter sowing indoors or, for overwintering types, an August sowing that is already past.
Head lettuce. Needs more time than the country has. Loose-leaf instead.
The category nobody writes about: sowing now for spring
This is where September stops being the end of something and becomes the start of something, and it applies even in zone 3 where outdoor sowing for this year is finished.
Overwintering spinach. Sow late September so plants reach three or four true leaves before hard frost, then leave them. They sit dormant under snow or mulch and resume growth the moment the light returns in February. You get spinach four to six weeks earlier than any spring sowing can manage, from plants with established root systems.
Overwintering onions and garlic. Onion sets planted in September, garlic cloves planted late September into October. Both root through autumn, sit out winter, and produce considerably earlier and larger than spring plantings.
Mache, also sold as corn salad. Extraordinarily cold hardy, survives temperatures that kill everything else, and can be sown right through September into October in most zones. It grows slowly through winter and gives you salad in a month when nothing else in the garden is alive.
Winter purslane, also called claytonia or miner's lettuce. Same principle. Sow in September, harvest through the coldest months. Mild, succulent, and genuinely productive in conditions where you would expect nothing.
Land cress and winter cress. Hardy, sharp-flavored salad leaves for the same slot.
Cover crops, on any bed you are not sowing. This is the most valuable thing most American gardeners could do in September and almost nobody does it. Winter rye sown now germinates fast, holds the soil through winter rain, suppresses spring weeds, and adds substantial organic matter when you turn it in. Crimson clover fixes nitrogen as well. Oats winter-kill in zones 3 to 6, which is convenient because they collapse into a mulch you can plant straight through.
Broadcast at two to three pounds per thousand square feet, rake lightly, water once. Then ignore it until spring.
An empty bed over winter loses nutrients to rain, grows weeds, and compacts. A bed under a cover crop improves.
Protection, which buys you three to six weeks
For anyone whose window is too short, this is how you extend it.
Row cover. Lightweight fabric over hoops. Adds four to six degrees of frost protection, which sounds trivial and typically translates to two to four weeks of extra growing at each end of the season. Cheap, reusable, and the single best value season extension there is.
Cloches. Anything transparent over an individual plant or a short row. Cut-off plastic bottles work perfectly well for small plants. Watch for overheating on sunny days.
Cold frames. A glazed box over a bed. Adds eight to fifteen degrees, which in zones 5 to 7 means salad through most of the winter. More investment, considerably more return.
Low tunnels. Plastic sheeting over hoops. Somewhere between row cover and a cold frame in both cost and effect. Ventilation matters, because a closed tunnel on a sunny October day cooks what is inside it.
Mulch, for the hardy crops. Straw piled over carrots, parsnips and beets lets you leave them in the ground and dig as needed well into winter. They store better in the soil than in a shed.
One practical point. Protection helps most in the shoulder weeks. It does not create growing conditions in December when light levels are the actual constraint. What it does is stop an early frost killing a crop that had three more productive weeks in it.
Regional summary
Zones 3 and 4. Outdoor sowing for this year is effectively over by mid-September. Focus on overwintering spinach, garlic, onion sets, mache, and cover crops. Under a cold frame, fast salad leaves are worth trying. This is a month for setting up next spring.
Zone 5. Radishes, arugula, mizuna, spinach and baby lettuce in the first two weeks. Cover crops on everything else. Overwintering spinach and garlic late in the month.
Zone 6. Comfortable for the whole fast list and most of the middle group if you sow in the first ten days. Kale sown now will overwinter. Garlic goes in at the end of the month.
Zone 7. A proper sowing month. Everything on both lists. Carrots and beets are viable. Succession sow salad leaves right through.
Zones 8 and 9. September is peak fall planting, not a last chance. The whole list, sown across the month rather than rushed. This is the best growing weather of your year for these crops after a brutal summer.
Zone 10. Your main season is starting. Sow everything, including things the rest of the country grows in spring.
Pacific Northwest. Mild and wet. Excellent for brassicas and salad, difficult for anything that resents wet feet. Raised beds and grit help. Overwintering crops do particularly well.
Mountain west. Short season, intense light, unpredictable frost dates. Treat yourself as one zone colder than the map says and lean on protection.
Common September sowing mistakes
Sowing on the calendar rather than the forecast. Your frost date is an average. A cold year can bring it forward by two weeks and a warm one push it back by three. Watch the ten-day forecast from early September.
Not adjusting days to maturity. Seed packets assume long summer days. Add ten to fifteen percent for September sowings and more for October.
Leaving beds empty. The single most common waste. If you are not sowing food, sow a cover crop. It takes twenty minutes and pays back in spring.
Sowing too thinly because it feels late. Germination rates are good in September soil and thinning is easy. Sowing sparsely because you are pessimistic just gives you gaps.
Forgetting to water. Early September soil dries out fast and germinating seed needs consistent moisture. This is the same failure that ruins August sowings and it persists into the first half of September.
Skipping the thinning. Applies more in autumn than in spring, because slow growth makes crowding more damaging. Overcrowded fall crops produce nothing usable.
Sowing brassicas without protection. Cabbage moths are still active in September in most zones and a young kale plant can be stripped in days.
Assuming frost is the end. Kale, spinach, mache, turnips, winter radishes and carrots all take hard frost. Several improve after it. Pulling everything at first frost throws away weeks of harvest.
Frequently asked questions
Is it too late if I'm reading this in late September?
Depends on your zone. Zones 7 and warmer still have plenty of time for the fast list. Zones 5 and 6 should focus on overwintering crops, garlic, and cover crops. Zones 3 and 4 should skip to next spring, and use the month to build a cold frame.
Can I sow into beds where tomatoes just came out?
Yes, but not brassicas or other tomato-family relatives, and work in some compost first. A bed that has carried a heavy summer crop is depleted. An inch or two of compost forked into the top few inches is enough.
Do I need to fertilize September sowings?
Light feeding helps. The soil is often depleted after summer cropping. Compost worked in before sowing, or a balanced organic feed once seedlings are established. Avoid heavy nitrogen late in the season, which pushes soft growth that frost damages.
Will things germinate in cooling soil?
Most of this list prefers it. Spinach, lettuce, arugula and Asian greens all germinate better at 60 to 70°F than at 80. Carrots and beets slow down noticeably below 60, which is why they need sowing early in the month in cooler zones.
How do I protect from cabbage moths this late?
Row cover from the day you sow, sealed at the edges. It is easier than dealing with caterpillars later, and it doubles as frost protection once the weather turns.
What about slugs?
Autumn is peak slug season. Damp cool weather and tender seedlings. Beer traps, copper tape around beds, going out with a torch after dark, or iron phosphate pellets which are safe around pets. Newly germinated seedlings are the most vulnerable stage.
Can I still start seeds indoors in September?
For transplanting out, only in zones 8 and warmer, and only for fast brassicas. In cooler zones, indoor sowing in September is for windowsill salad rather than for the garden.
Should I dig the beds over before winter?
Increasingly the answer is no. Leaving soil structure intact and covering it, either with a cover crop or with mulch, does more for soil health than autumn digging. Digging exposes soil to winter rain and destroys structure.
When do I sow garlic?
Late September in zones 3 to 6, October in zones 7 and 8, November in zone 9. It wants four to six weeks of root growth before the ground freezes.
Is there any point sowing flowers in September?
Yes, several hardy annuals sown now overwinter as small plants and flower far earlier and larger than spring sowings. Calendula, larkspur, bachelor's buttons, poppies, sweet peas in mild zones. Same principle as overwintering spinach.
Final thoughts
September is not the end of the sowing year unless you live somewhere very cold, and even then it is not really the end, it is a change of purpose.
If you take one thing from this, do the frost date arithmetic before you do anything else. Find your date, count the days, take off two weeks for slowing growth. That number tells you which of the three lists above applies to you, and it stops you either wasting seed on crops that cannot mature or leaving beds empty when you had eight weeks in hand.
If you take a second thing, sow spinach. Late September, and either pick it in November or leave it to overwinter and pick it in February. It is the best-value sowing available this month in almost every zone, it germinates better now than at any other time, and overwintered spinach with an established root system produces earlier than anything you can sow in spring.
And if you take a third, do not leave beds bare. Winter rye takes twenty minutes to broadcast and rake in. It holds your soil through the rain, suppresses next spring's weeds, and adds organic matter you would otherwise have to buy. An empty bed over winter is the one genuine waste in the September garden.