Seasonal guide

What to Plant in September for a Fall Harvest

5 min read

September has a reputation as the month it's all over. Somewhere between the last of the tomatoes and the first cool morning, a lot of gardeners stop sowing anything.

But in most gardens that's early. In some climates it's the exact opposite of what's happening, because September is when the good part of the year finally starts.

So this isn't really a list of dates. It's a way of figuring out which September you're having.

The short answer: in most gardens you can still sow arugula, radishes, mustard greens, mizuna and tatsoi, and early in the month spinach, leaf lettuce, bok choy and turnips. Garlic and overwintering greens go in now too. And in a hot climate, September opens the whole cool-season list. How much time you have depends on how much good season your garden has left, and that's local.

Why fall sowings take longer than the packet says

Growth slows in fall. Most planting advice leaves that out, and it's what matters most right now.

A radish that took 25 days in May will take noticeably longer sown in mid September. Not because anything's wrong, but because a plant grows on the light and warmth it actually gets, and both of those are on the way down. Days are getting shorter by a couple of minutes each morning, the soil is giving back the heat it stored all summer, and every biological process in the bed runs at the pace those two set.

Seed catalogs measure days to maturity in the good part of the season, when conditions are pushing rather than easing off. Fall sowings typically run behind that number. Sometimes by a few days, sometimes by weeks, depending on how quickly your particular season is cooling.

Which is why "is there still time?" has a different answer in every garden, and why a single cutoff date has never worked. It depends on how much warmth and light your garden has left. Verna reads the climate at your coordinates and works that out plant by plant, so what you get is an answer for your garden rather than a rule someone wrote for theirs.

What still has time: the September sowing list

There's more room than most people think, as long as you pick for speed and accept smaller.

The fastest things still worth sowing. Arugula is the quickest useful green there is, roughly 21 to 35 days, and it actually prefers this weather to July's. Spring radishes are about the same, 22 to 35 days. Mustard greens run 30 to 45. Mizuna and tatsoi, both underrated and both very cold-tolerant, sit around 35 to 50. These are the ones that can still finish in a short window.

The ones that need a little more room. Spinach (40 to 50 days), leaf lettuce (40 to 55), bok choy (40 to 55) and turnips (40 to 60) all want more of September than the fast greens do, but they're also the ones that get better as it cools. Spinach in particular is worth the space: it's genuinely hardy, and it holds in the garden a long time once it's up.

Cut-and-come-again is your friend right now. You don't have to grow a full-sized head of anything. Sowing greens thickly and cutting them small turns a 55-day plant into a 30-day one, which changes what fits.

Skip the long ones. Broccoli, cabbage, cauliflower and Brussels sprouts from seed are past it almost everywhere in September. If you want them, buy transplants, which effectively hands you back the six weeks the seed would have spent as a seedling. Even then, check whether your season has room.

Overwintering: the sowings that are meant to sit still

This is the part of September that most gardeners never try, and it's the highest-value thing in the month.

Some hardy greens can be sown late, come up, reach a few inches, and then simply pause for the winter. They aren't dying and they aren't failing. They're waiting. Then in late winter, while everything else is still bare, they start again and give you a harvest weeks before a spring sowing could.

Spinach is the classic. Mache (corn salad), claytonia, arugula and some kales do the same thing. In a cold place they'll want a row cover or a low tunnel over them; in a mild one, often nothing at all.

Garlic belongs to this category too, though it works on its own schedule. It goes in during fall, sits through winter, and comes out the following summer. Verna treats garlic separately for exactly that reason, and there's a whole post on getting it right.

A row cover changes the arithmetic

Worth knowing before you decide the month is over: a layer of lightweight fabric over a bed holds a few degrees of warmth, blunts the wind, and keeps frost off the leaves. That's often the difference between a sowing that finishes and one that stalls just short.

It doesn't extend your season indefinitely. But it does buy back some of the fall slowdown, and it's the cheapest way to keep greens going well past the point where the open bed gives up.

In a hot climate, September is when planting starts

Everything above assumes fall is closing in. For a large part of the US it isn't, and September is more like what April is elsewhere.

In the desert Southwest, the Gulf, inland California and much of Texas and Florida, summer is the hard season. It's the stretch where things stop setting fruit, greens bolt on contact and the soil is too hot for seed to germinate at all. September is when that breaks. Soil temperatures drop back into the range where seed will actually come up, the nights ease, and what follows is a long, generous run of cool-season growing that lasts until spring.

If that's your garden, September isn't the tail end of anything. It's the starting line, and the standard planting calendar has been giving you backward advice your whole gardening life. There's a full post on how the warm-climate year is shaped.

Why September seeds don't come up (and the fix)

Early September soil is often still summer-warm, which is a problem for exactly the plants you want to sow now. Lettuce and spinach both germinate poorly when the soil is too warm, and spinach in particular often refuses outright.

The fix is the same one that works in August: sow a little deeper, keep the top layer of soil damp instead of watering deeply and rarely, and shade the row until the seedlings are up. The full explanation is here, because it's the single most common reason a fall sowing never appears.

Where Verna sits in this

The reason a September planting list is hard to write is that the version of it is different for every location.

Verna carries a last-sow point for each plant if applicable, worked out against your own frost window rather than a shared calendar date. Those points aren't close together: some plants stay open until just a few weeks before the window closes, and others shut months earlier. And it holds the rest of what decides a fall sowing too, the soil temperature each plant needs to germinate, how hardy it is once it's up, how long it takes to get there.

So instead of asking whether it's too late in general, you can ask whether it's too late for spinach, in your garden, this week. That's a question that has an answer specific to you.

The short version

September is a sowing month in most gardens, just a narrower one than August. Pick for speed, sow a bit thicker, cut smaller, put in the things meant to overwinter, and let the long ones wait for spring.

And if the summer was the hard part where you garden, this is the month you've been waiting for.

See what still has time in your garden

Verna maps sowing, transplanting, and harvest timing to your exact spot.