Sow These Seeds in Mid-Autumn

23 September 2023, written by Benedict Vanheems

Autumn has arrived, and while growth might be slowing down there’s still sowing to be done. This is a great time to start off some winter-hardy veggies, give your soil a boost with a nourishing cover crop, and sow a truly unusual mystery vegetable which I’ll reveal at the end…

Salad Onions

Salad onions, also known as spring onions or scallions, are a staple in my garden. There’s still time to sneak in a final sowing if you can get them in pronto and offer a little bit of cold protection.

It’s important to choose a really hardy variety to sow this late in the season. Sow direct into weed-free soil that’s had a little organic fertiliser added. Rake the soil to give a fine, crumbly texture. Mark out rows spaced just 4in (10cm) apart, and about half an inch (1cm) deep.

Sow one or two seeds every half inch (1cm) to give the resulting seedlings enough space to grow without the need to thin them. Once they’re sown, cover them over with soil, then water along the rows. Keep the seedlings weed-free at all times. They’ll tick over during the winter then push ahead in early spring to give the very earliest salad onions.

One of the main reasons behind poor germination in onions of any sort is using old seed. Onion seed doesn’t store for long at all, so to avoid disappointment I’d recommend using super-fresh, recently purchased seed.

To protect my onions from the worst of the cold I set up my temporary cold frame, which uses old windows. The sides are cut to size, held in place with pegs made from cut-down bamboo canes, and the window just sits on top. I lift off the window during milder spells to encourage good airflow for the seedlings.

Winter Lettuce

Winter lettuces are hardy varieties that can cope with colder temperatures. Many have names that hint at their hardiness, for example ‘Winter Density’, ‘Arctic King’ or ‘Winter Gem’, but you can always check the variety description to see if it’s suitable for winter growing. They can be sown throughout winter, particularly if you can offer a little protection from the elements.

You can sow winter lettuces directly into the soil, where they are to grow, but I prefer to start mine off in plug trays to make it easier to protect them from slugs and other pests while they’re still very small. Sow a couple of seeds per plug, then thin them once they’ve germinated to leave just the strongest seedling in each plug.

Before planting, add an inch-thick layer of garden compost to the bed. Plant the seedlings 8in (20cm) apart in each direction. To keep them cosy one option is to set up a simple polythene-covered miniature tunnel. Just pop sections of piping onto upright pegs, then secure a ridgepole between the hoops for sturdiness and to support the cover. Cover with a clear plastic sheet, well secured at the edges.

Harvest your winter lettuces by taking a just few outer leaves from each plant at a time when they reach a useable size.

Cauliflower

Cauliflowers are one of those super-versatile vegetables worth making space for if you can. I love them in curries, soups, and as a bloat-free alternative to rice. They’ve got a bit of a reputation for being difficult but you can keep them growing steadily, uninterrupted, by potting them on and planting out promptly, and by keeping them well-watered.

Sowing cauliflowers in autumn offers a not-to-be-missed chance to bag yourself a super-early harvest next summer. Early cauliflowers are easier to grow because they’re less likely to get thwacked back by the heat of midsummer, and they should be harvested before the worst of those hungry caterpillars are about. So, while you’ll need to overwinter the seedlings in a cold frame or under similar protection they are, in fact, a far less troublesome prospect.

Sowing your cauliflower seedlings under cover also helps keep them well away from pigeons, slugs, and other winter pests. Any sieved multi-purpose potting mix will be just fine. They should germinate within two weeks. If it’s colder where you are, perhaps bring them inside your house to germinate where it’s a bit warmer, before bringing them back out to your greenhouse or cold frame.

Once the seedlings are up, carefully remove them from their containers and, handling them by the leaves, transfer each into their own 3-inch (7cm) pots to grow on and keep ticking over til it’s time to plant them outside in spring. At that point they should be around 6in (15cm) tall, and can be planted about 1.5-2ft (45-60cm) apart.

Winter Cover Crops

With more beds being vacated there’s a window of opportunity to sow a winter cover crop (also called a green manure). Cover crops are sown specifically to give something back to the soil, such as improving soil structure or fertility – or both! - shielding the soil from heavy rains or, in summer, protecting it from the heat.

I’m going to use a fantastic winter cover crop mix which contains deep-rooted rye and nitrogen-fixing vetch. These are hardy plants that will sprout and spread quickly, helping to keep the ground covered over winter. I’ll dig or hoe it in later in spring, a few weeks before it’s time to plant my food crops. All that biomass will then rot down into the soil, contributing valuable organic matter which will help next year’s crops to really thrive.

Scatter the seeds onto the soil then rake the area over so the seeds come into good contact with the soil. The soft autumn rains will get it sprouting in no time, and then you can just leave it to do its thing. Cover crops like this are ideal if, like most gardeners – me included – you struggle to make enough compost. We’re literally producing fresh, new organic matter out of thin air – and rain!

Oyster Leaf Plant

Now what about our mystery crop? It’s the oyster leaf plant (Mertensia maritima)! This fleshy-leaved plant is often described as ‘the vegetarian’s oyster’ because of its salty tang and hints of seafood flavour. It originates from the rocky shores and shingle beaches of northern Europe, including Scotland, and much of maritime Canada, Alaska, and New England.

The seed packet recommends storing seeds in the fridge for two weeks before sowing, which I’ve done - presumably this helps to break the seeds’ dormancy and prime them for sprouting. Originating from the coast, the seeds can survive up to two weeks submerged in seawater and will tolerate very cold temperatures – these guys are tough cookies!

Oyster leaf plants prefer well-drained, sandier soils, so I’m sowing the seeds into an multi-purpose potting mix with a few handfuls of sharp sand added to give better drainage.

The cold weather treatment continues from here as they need an ongoing spell of colder weather to germinate, so I’m going to keep them in a shaded cold frame for the winter. The seedlings should then – fingers crossed – appear sometime in spring at which point they’ll be carefully separated and potted on into their own containers. They can go into any well-drained soil that gets good morning light but is shaded from the warmer afternoon sun. I think I’ll play it safe by continuing to grow them in containers of that well-drained mix. Can’t wait to give this a taste!

There’s more to be done over the coming weeks, and next week I’ll be outlining some key jobs to get your garden shipshape and ready for winter.