Sowing the First Brassicas of the Year - Brassica Growalong (Part 2)
Replicated from an article I wrote for Garden Folk Magazine, March 2026.
There’s a particular kind of hopefulness that arrives with the first sowings of the season. The light is shifting, the compost is cold but promising, and suddenly the whole year opens up in front of you.
Last month I talked (a lot) about brassicas, and that’s going to continue through the year as I host Garden Folk Magazine’s Growalong. Brassicas are the stalwarts of the veg garden, the crops that carry us through the hungry gap and reward patience with real substance. This month, we’re putting that knowledge into practice and sowing the first seeds of our growalong.
If you’re joining in, don’t worry about having a fancy setup. A bright windowsill, a few modules or small pots, and a bag of seed compost is all you need. Brassicas are wonderfully forgiving at this stage. Steady, reliable, and quietly determined. Perfect for all gardeners irrespective of their experience.
Coming up you’ll find detailed sowing instructions for each of our five crops, plus a clear sense of what to expect as the month progresses. Think of this as your month‑one roadmap.
And before we dive into the “how”, let’s talk about where. Because everyone’s setup is different; the good news is, brassicas are wonderfully adaptable.
Choosing Your Growing Setup
A bright windowsill
A perfectly good place to start. Brassicas don’t want heat. In fact, they prefer cooler conditions. A windowsill gives you:
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steady light
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cool temperatures
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easy access for watering and turning
Just avoid radiators underneath, as warm air encourages leggy seedlings.
Heat mat
Not necessary for brassicas, but not entirely harmful. If you’re using one for other crops you may as well get the most out of it by allowing your brassicas to have a fleeting visit there. If you do use one:
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place brassicas on the edge where it’s cooler
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remove them once germinated
They’ll be just as happy without it.
Grow light
Useful if your windowsill is dark or north‑facing. Under a grow light, brassicas will be:
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stockier
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less prone to leaning
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more uniform
But again — not essential.
Unheated greenhouse or cold frame
This is where I start mine, and it’s honestly the most natural place for them. Benefits:
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perfect cool temperatures
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bright light
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slow, sturdy growth
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no risk of overheating
Just protect from mice (they love brassica seeds) and keep an eye on watering, compost dries out faster than you think on sunny days.
THE FIVE GROWALONG CROPS
Below are the sowing instructions for each crop, plus what to expect as the month progresses once you’ve sown them. But please, don’t forget this is just my advice, not rules you must follow to the letter! Plants are unpredictable and will often do their own thing in their own time, don’t worry if yours are growing at their own pace, not what I’ve written below.
1. Brussels Sprouts
How to Sow
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Sow in modules or small pots
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Cover lightly
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Keep cool: 10–15°C
By Week 2
Germination is steady and reliable with signs of the seedling usually between 4 and 8 days from sowing. Seedlings stay compact, with their first true leaves just beginning to form. Growth is slow. Sprouts take their time, but they should be starting to look sturdy and upright.
By Week 4
Pot on into 9cm pots if roots are showing. Keep cool and bright.
2. Summer Cauliflower
How to Sow
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Sow in modules
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Cover lightly
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Keep at 12–18°C
By Week 2
Germination is usually from 7 to 12 days from sowing. Seedlings may lean towards the light, so turn trays daily. True leaves begin to appear, and the plants look delicate but determined.
By Week 4
Pot on if needed. Avoid stress, cauliflower is sensitive to sudden changes.
3. Kale
How to Sow
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Sow in modules or a shallow tray
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Cover lightly
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Keep at 10–18°C
By Week 2
Fast germination, with seedlings typically appearing 4 to 7 days after sowing and strong early growth. True leaves appear quickly, and seedlings look upright and confident.
By Week 4
Pot on or thin to one per cell. Kale is forgiving and easygoing.
4. Kohl Rabi
How to Sow
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Sow one seed per module
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Cover lightly
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Keep at 12–18°C
By Week 2
Germination is usually even, with seedlings appearing 7 to 12 days after sowing. True leaves appear and stems begin to thicken slightly, the first hint of the swollen stem to come.
By Week 4
Start hardening off on mild days. Kohl rabi is tough and can go out earlier than most brassicas.
5. Savoy Cabbage
How to Sow
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Sow in modules
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Cover lightly
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Keep cool: 10–15°C
By Week 2
Steady germination from day 4 to 7 after sowing with strong, compact seedlings. True leaves begin to show the first suggestion of crinkle.
By Week 4
Pot on if needed. Keep cool and bright.
WHAT YOU’LL BE DOING 4 WEEKS AFTER SOWING
By the end of the first month, you’ll be:
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Potting on anything that’s outgrown its module
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Hardening off kale and kohl rabi on mild days
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Turning seedlings daily
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Watering lightly, brassicas hate soggy compost
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Keeping everything cool
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Feeling quietly proud of your little forest of seedlings
This is the slow, steady part of the season. the foundation for everything that comes next.
IF THINGS GO WRONG (AND WHY THEY MIGHT)
Seedlings are tall and leggy
Cause: Too warm, not enough light.
Fix: Move to a cooler, brighter spot. Turn daily.
Seedlings collapsing at the base
Cause: Damping off (fungal).
Fix: Improve airflow, water less, use clean pots. You may need to resow.
Patchy germination
Cause: Uneven moisture, cold compost, or mice (greenhouse culprit!).
Fix: Resow. Use a lid or mesh if mice are around.
Yellowing leaves
Cause: Overwatering or lack of light.
Fix: Let compost dry slightly between waterings. Move to brighter spot.
Seedlings not growing after germination
Cause: Too warm. Brassicas stall in heat.
Fix: Move to a cooler place, an unheated greenhouse or cold frame is perfect.
READER Q&A
Last month I ask you to send in your questions for the growalong, here’s what came in along with some answers that will hopefully help you have successs with growing yours.
“Do I need a propagator for brassicas?”
No, they prefer cool conditions. Whilst a propagator can spur on germination, being say there too long is more likely to make them leggy.
“Can I sow them straight outside?”
Whilst you can direct sow Sprouts and Cauliflower in March I wouldn’t. It’s too cold and too wet. Indoor or greenhouse sowing gives you a strong start. That said, all 5 we’ve included in the growalong are typically good for direct sowing in April, so if you want to hang on a month then do, or maybe experiment and do a few inside and a few direct later. Seeing which methods work best for you is always a good thing to do.
“My seedlings are leaning towards the window, is that bad?”
Totally normal. Just turn the tray once a day and they’ll straighten up.
“When can I plant them out?”
Not until they’re sturdy, hardened off, and the weather settles. Usually April for kale and kohl rabi, May for the others. I’ll be waiting until May to get all of mine planted out, once the area is ready for them.
“Do I need to feed them?”
Not at this stage. Seed compost has everything they need for the first few weeks.
And a top tip from Collie Flower’s own Head Gardener Hazel “to encourage strong, firm stems on your brassicas (and many other plants) don’t forget to simulate a breeze for them, a light wafting with your hands once a day just to give them some movement is enough, or a short period with a fan blowing on its gentlest setting from a distance, is all you need but it helps.”
So that’s where we’ll leave things for this month. The quiet, hopeful beginning of the season, when a tray of tiny brassica seedlings feels like a promise to your future self. These early sowings don’t ask for much: a cool spot, a bit of light, and your steady hand. If you’d like more detailed step‑by‑step guidance, you’ll find expanded sowing notes over on the Collie Flowers website, and even more support inside the Sow & Grow app, where the growalong is unfolding week by week.
Next month, in the April edition, we’ll be potting plants on: hardening off, preparing beds, tackling early pests, and possibly considering planting out the first of our cool‑season crops – it all depends what the weather is like between now and then. It’s the moment everything starts to feel real, and I can’t wait to walk you through it.