The 7 Seeds You MUST Start in September

14 September 2026, written by Benedict Vanheems

If you’ve struggled to grow anything this summer because of the heat, now that it’s finally cooling down it’s time to get back in the game! There’s plenty to plant – if you act fast. Think colourful salads, leafy classics, and a mystery plant that won’t feed you right now but will feed your soil, setting you up for better harvests next season…

Winter Lettuce

Let’s start by myth-busting a common misconception: lettuce isn’t just a summer crop! Sow the right varieties now and you’ll be cutting crisp, fresh leaves from your garden from just over a month’s time, and on right through to next spring. I’m not sure there’s anything quite as joyful as picking luscious leaves in the depths of winter!

The variety ‘Winter Density’ is my pick for sheer reliability. It’s sweet, crunchy, and happy to shrug off a proper cold snap, while ‘Arctic King’ is the absolute tank of the lettuce world, bred to sit tight through frost after frost.

I start my lettuces in plug trays, two seeds to each plug, then cover them with just the lightest sprinkling of potting mix. One quirk with lettuce seed at this time of year is that if the soil or potting mix is still very warm from summer, the seeds may refuse to germinate – something known as thermal dormancy. So, if it’s still baking hot where you are, sow your lettuce in a shadier spot or on an indoor windowsill that’s out of direct sun.

Once the seedlings have a few adult leaves, transplant them about 10in (25 cm) apart, ideally somewhere with a bit of cold protection. For me that will mean in the greenhouse, but a cold frame – even an improvised one – or under some sort of cloche or mini-tunnel would work just as well. We need to protect the plants from the heat now and, in cooler climates, from the cold later in the season. A little protection will buy you a few extra weeks of growth as things turn colder and wetter.

Cold frame — A couple of panes of glass is all most hardy salads need to protect them through winter

More Hardy Salads

If you think winter salads begin and end with lettuce, you’re in for a pleasant surprise because there is in fact a whole cast of characters that are even hardier! First up is claytonia, also known as winter purslane or (my favourite name for it) miner’s lettuce. It’s so-named because it was a winter staple for 19th-century gold prospectors during the California Gold Rush, when its vitamin C-rich leaves helped to stave off scurvy through those long winters in spectacularly remote mining camps – which tells you everything you need to know about how tough this plant is. It happily stands up to temperatures that would flatten most salad leaves, its lovely leaves remaining soft, mild and succulent right through the depths of winter. What a trouper!

Other reliable winter salad crops include mache, also known as corn salad or lamb’s lettuce – which despite its sheepish name might just be the hardiest salad of all – and peppery mustards to bring a bit of heat to the winter salad bowl.

There are a few ways we can grow these resilient salads. The first is to sow them into plug trays in the same way as lettuces, then plant them into their final positions in about a month’s time, once they’re big enough to handle.

Frosty claytonia — Despite its soft, succulent leaves, claytonia is extremely winter hardy

Alternatively, the seeds may be sown thinly across the surface of pots or trays and then covered with a little sifted potting mix until the seeds just disappear from view, before pressing down gently and watering. Once they’ve germinated, thin the seedlings out by removing any excess so they are no closer than about 4in (10 cm) apart.

The final option is to simply sow directly where they’ll grow. Remove any weeds then rake the soil to give a nice even texture. Mark out rows about 10in (25 cm) apart, then sow into the rows, cover the seeds over, and give them a good water.

Once the seedlings that come up and have grown a few leaves, thin them out to around 6in (15 cm) apart. Then as the weather cools off, cover them with a tunnel or even just lay panes of glass over the top of the bed to keep them snug.

Treat these as cut-and-come-again crops, snipping what you need, when you need it, then letting the plant regrow. By doing this, just one sowing can keep your salad bowl full for months to come. Harvests may ease off a bit during the depths of winter but by early spring they’ll be off again, giving a rush of leaves before eventually stretching out to flower.

Spinach

A word of warning: we have a bit of a deadline for this one, because if we want a proper spinach harvest before winter really bites, it needs to go in asap.

Spinach sown now successfully strikes a fine balance. Much earlier, and lingering summer warmth could trigger that same thermal dormancy I mentioned with lettuce, or heat might push plants to bolt (flower and go to seed) before you’ve had a single harvest. Any later, on the other hand, and shortening days mean seedlings won’t get properly established before growth grinds to a halt for winter. Right now is the sweet spot!

Sow directly into shallow rows or drills, about half an inch (1 cm) deep, with rows spaced around a foot (30 cm) apart. Drop one or two seeds roughly every 2in (5 cm). Cover with soil and firm the seeds in, then water well. Keep the soil consistently moist while germination gets underway, because spinach hates drying out.

Once seedlings are up, thin them so that the little plants are about 4in (10 cm) apart. Use the thinnings as the very first, tiniest salad harvest – waste not, want not!

Plants will grow steadily through autumn, offering tasty leaves as the weeks go by, then largely pause over the coldest months before rocketing back into growth in spring, giving up tender leaves weeks before anything sown fresh could possibly catch up. A row cover or other protection will keep them ticking along and protected from the very worst of the weather.

If things are on the cool side where you garden, you may not get any pickings this side of winter but, rest assured, come spring there’ll be more than enough to go round!

Salad Onions

Now for a crop that rewards patience with an absolutely stonking payoff. I’m talking overwintered salad onions.

Sow them now, and in spring when others are just starting to think about sowing their salad onions, yours will already be standing tall, crisp and just about ready to pull, often a full six to eight weeks ahead of spring sowings. That is what I call a head start!

I always reach for a winter-hardy strain of ‘White Lisbon’ for sowing at this time of year. It’s specifically bred to shrug off frost and cold, wet soil, but other winter-hardy varieties are available too.

Salad onions couldn’t be easier: sow directly where they’re to grow, about half an inch (1 cm) deep in drills spaced around 6in (15 cm) apart. Scatter the seed fairly liberally along the row, and cover back over with soil. There will be little need to thin them out unless they’re really rammed in, because the stems are classically pencil-thin.

Germination will be a touch slower than a spring sowing thanks to the cooling soil, so don’t panic if you don’t see seedlings for a couple of weeks. But once they’re up, plants will grow on steadily into small, hardy little onions. They’ll sit tight through the worst of winter and then explode into growth the moment the days start lengthening again.

Winter tares seeds — Broadcast winter tares across the ground to suppress weeds and protect the soil against winter weather

Winter Tares (Hairy Vetch)

And now for the mystery plant you’ve been waiting for! It’s a sowing that will feed not you, but every crop you grow here next year: winter tares, also called vetch.

The fabulous thing about winter tares is that they are legumes, which means they pull nitrogen straight out of thin air, as if by magic, and use bacteria already in the soil to lock it into little nodules on their roots. Come spring, dig them back into the ground to release all of that captured nitrogen straight back into the soil to feed nitrogen-hungry crops like cabbages.

And that’s not all. The thick, tangled growth of winter tares will smother weeds all winter long, protect bare soil from being battered by winter rain or eroded by snowmelt, and its extensive root system will help break up heavy, compacted ground. It is genuinely one of the hardest-working plants you can sow all year – and all for the price of a packet of seeds!

Sowing couldn’t be simpler. Clear any weeds, rake the soil, then scatter the seeds evenly across the surface. There’s no need to be too precise. Rake the seeds lightly into the top inch or so of soil, then water if the ground’s dry. And that really is that!

One thing to bear in mind is that winter tares can release compounds into the soil that inhibit the germination of small seeds like carrots or spinach, so leave it around a month after digging it in before sowing. Transplants of young seedlings, on the other hand, will be completely unaffected.

If you’d like exact sowing dates for anything we’ve sown today, tailored to your precise location, give our Garden Planner a try. It uses data from your nearest weather station to tell you exactly when to sow, plant and harvest. You can try it out completely free!