When it comes to seed sowing in the UK, March is where things start to get busy! Not for you, though – you’ll have everything planned out using these guides. Here are just some of the seeds you can sow in March in order to grow food and flowers.
This is a pretty big list. If you find it overwhelming, try breaking down your options with this handy checklist or waiting until April to sow some of these seeds. If I have to choose, I start my tomatoes and flowers first, then other crops as space opens up on my window sills. As you gain experience, you’ll figure out what works best for you.
Tomatoes
Whether you’re growing tomatoes outdoors or under cover in a polytunnel or greenhouse, March is an excellent time to sow them. Your seeds will need heat to germinate. This can come from a propagator light, lid, or radiator near your window sill. If you’re in the market for beautiful heirloom tomatoes, check out all my favourite niche tomato seed suppliers. Once your tomato seedlings are about four inches tall, you’ll need to move them into individual pots, and keep them in good natural light so they don’t go too leggy.
Tomato warning: it’s all well and good deciding to grow 17 kinds of tomato, but when it’s early April and you have 30 odd seedling pots that all need window space (along with all your other crops and flowers), you may wish you’d staggered your sowing! This has of course never happened to me. Ahem.
Courgettes
Should you intend to terrorise your family with an endless supply of courgettes, excellent news: you can sow them in March! Sow the seeds on their sides and give them plenty of heat and light. Despite the fact that there are so many interesting varieties available, try to restrain yourself; few families need more than two plants. When it comes to harvest time, courgettes are the only crop I struggle to give away. I love courgettes so this makes me very sad. Fortunately, they are easy to hide in my family’s meals…
Cucumbers
Cucumbers really need heat to grow – not just for seed sowing, but for the plants themselves. Sow them in March if you’re going to grow them under cover; if you’ll be growing them outdoors, wait until late March or early April. Once they germinate, they are big plants that grow fast, so they won’t take long to establish and can take up a lot of space on your windowsill.
Lettuce, spinach, rainbow chard and Asian greens
All kinds of lettuce can be sown indoors now, and lamb’s lettuce can be sown outside as it is pretty hardy. I find lettuce does much better sown in my unheated polytunnel as my window sill just isn’t light enough, and they get leggy. Grow lights may help with this. While sowing this way can make your harvest slightly earlier, you’ll get similar results from sowing your lettuce directly outside in April and May.
As much as I dislike using a catch-all term like “Asian greens,” it best describes the cabbages and mustard leaves that come from that continent and do so well in our British gardens. While pak choi and bok choi are well known, I would encourage you try try tatsoi, which is succulent, sweet and quite beautiful to look at as it grows. Asian greens are speedy growers, and will be ready to go outside in just a few weeks.
Carrots and parsnips
Carrots do best when sown directly outside where you intend to grow them. They really need to stay moist in order to germinate, which can take up to a month; make sure you keep them well watered, or even cover the area with damp cardboard for the first few weeks (this helps to stop squirrels and other animals digging the seeds up, too). Carrots need deep, free draining soil free of roots and stones. Don’t add lots of extra fertiliser as the carrot can end up misshapen as it tries to grow towards all the different nutrients.
Parsnips can be sown in the same way, though they often take longer to germinate and longer to grow. Rumour has it that if you can get parsnips to germinate on your first try, Monty Don appears in a fancy hat to sing a few rounds of 500 Miles by the Proclaimers.
Peas and mangetout
I sow my peas in March on a sunny windowsill. The seed peas are really prone to mould at this time of year, so try not to overwater and keep them away from direct heat like radiators. They have long roots so need a seed tray or pot at least three inches deep. Peas can go outside later in April (or in late March to an unheated polytunnel or greenhouse for a cheeky early crop).
Brassicas
You can sow cabbages, broccoli, cauliflower, sprouts, kolrhabi, swede, turnips and all kinds of brassicas in March. There is more detail in my February guide.
Spring onions
Sow your spring onion seeds five or six seeds to a pot so that they grow in bunches. They need a bit of heat to germinate.
Potatoes
Early potatoes can be planted outside in March. You can grow in in-ground and raised beds, in grow bags, or in large pots (at least 40cm deep and wide, but preferably bigger. Check out the large planters I use on Amazon). Make sure that the soil is free of roots and stones, and consider adding a natural fertiliser like chicken manure pellets to beds that need refreshing. Cover fresh plantings with net or mesh to stop animals digging them up.
Herbs
You can sow all your herbs now: parsley, dill, rosemary, thyme, chives, sage, and basil. Basil in particular needs heat to germinate. Sow it in clumps – five or six seeds to a pot – for a bumper harvest.
Broad beans
Broad beans can be sown directly outside in March in a spot that gets plenty of sunshine. They will come up in about a month. They do best in the ground or in very deep pots. Make sure you cover your sowing with mesh or wire to prevent the tasty seeds being dug up by animals and birds. They can grow to be several feet tall, so make sure you can support them and that they won’t shade other crops unintentionally.
Beetroot
Start sowing beetroot now on a sunny windowsill. If you’re growing it for use raw or in salads, sow three or four per pot or cell, and they will grow together in a cute little clump, staying small-ish, crisp and sweet.
Radishes
Radishes are some of the easiest crops that you can grow, which is why they taste like licking a Wetherspoons toilet (only joking – sorry, radish lovers!). In all seriousness: they are quite spicy and a bit of an acquired taste, but if that’s your kind of thing, they work well in salads, as pickles, or even roasted. Sow them in late March outside, where you intend to grow them. If you like turnips, you’ll like radishes.
Flowers: stocks, cornflowers, zinnias, nigella, asters, strawflowers, statice, aquilegia
A lot of these flowers – stocks, cornflowers and asters in particular – will grow fast, so be prepared to pot on within a few weeks. Sow them on your sunniest window sill, use growlights, or sow in a heated greenhouse if you have one. Flowers need high levels of light to thrive.
There will be other flowers to start in March too; these are just the ones I grow! Always check the backs of your seed packets for instructions.
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