How To Start Seeds Indoors (It's Easier Than You Think!)

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Let’s talk about one of my absolute favourite things to do when it’s still chilly outside – starting seeds indoors! There’s something magical about watching those tiny seeds burst into life on your windowsill. It feels like you’ve got a secret head start on the gardening season.

Now, I know the idea of setting up trays and lights might seem a bit much, especially when you can just buy little plants later on. But once you get the hang of a few basic things, it’s incredibly rewarding and opens up a whole new world of gardening possibilities.

In this guide, I’m going to walk you through everything I’ve learned about how to start seeds indoors – from avoiding common pitfalls to raising strong, healthy plants ready for life outdoors. Let’s dive in!

Rows of young watermelon plants are growing in seed trays inside a greenhouse, waiting to be transplanted into larger pots or a garden.

Why Bother Starting Seeds Indoors?

So, why go to the trouble when garden centres are full of plants come springtime? Well, for me, the benefits are huge:

Get a Jump on the Season

This is a big one, especially in regions with shorter growing seasons! Starting things like tomatoes, peppers, and chillies indoors weeks before the last frost means you actually get a decent harvest before autumn rolls back around. It seriously extends your growing time!

Way More Choice

Forget the standard varieties! Seed catalogues are like treasure troves. Want purple carrots? Striped tomatoes? Weird and wonderful flowers you’ve never seen before? Starting from seed is how you get them.

Save Your Pennies

Let’s be real, buying individual plants adds up fast. A packet of seeds often costs less than one plant and gives you dozens. Your wallet will thank you.

You’re in Control

You know exactly what soil mix you’re using (hello, peat-free options!), how much water they get, and that they haven’t been stressed out sitting on a shop shelf. You raise them right from day one.

That Gardener Feeling

Nurturing something from a tiny seed is so satisfying. It connects you to the whole process in a way buying plants doesn’t quite match. Plus, it’s something productive to do when it’s miserable outside!

Vegetable seedlings are grown in egg trays.

Timing is Everything: When Should You Sow?

Okay, this is super important. Get the timing wrong, and you can end up with sad, leggy plants way before it’s safe for them outside. Start too late, and you lose that valuable head start advantage you were aiming for. Timing really is the key to success here.

The secret lies in figuring out two things:

1. Your local last frost date

This is the average date things stop freezing in your specific location, and it varies wildly by state! I find that searching online for “last frost date [your zip code]” is the easiest way to get this.

2. The seed packet instructions

This is your specific instruction manual for each plant! It will usually tell you how many weeks before that last frost date you should start the seeds indoors (e.g., “Sow indoors 6-8 weeks before last frost”).

To figure out your sowing window, just count backwards from your estimated last frost date by the number of weeks recommended on the packet. That’s when you should aim to sow those particular seeds.

Rough Guide (Always check the packet!):

10-12 weeks before: Slow growers like onions, leeks.
8-10 weeks before: Heat lovers like peppers, chillies, aubergines.
6-8 weeks before: Tomatoes, brassicas (broccoli, cabbage etc.), lots of annual flowers.
2-4 weeks before: Fast growers like courgettes, cucumbers, squash (these guys hate root disturbance, so don’t start them too early!).

Quick tip: Don’t sow everything at once! Stagger your sowing based on what the packet says.

Closeup little cos lettuce vegetable sprout seeding in tray, organic planting preparation in natural farm.

Gathering Your Gear: What You Actually Need

You don’t need a fancy greenhouse, I promise! But having the right bits and bobs makes life much easier.

Seeds: Obvious, right? Get fresh ones from a decent supplier. Check the ‘sow by’ date.
Containers: Loads of options here!
- Seed Trays: Great for starting lots of seeds efficiently.
- Small Pots: Plastic or biodegradable ones (peat/coir). Good for plants that hate having their roots messed with later.
- Soil Blockers: A cool tool that makes little soil cubes, no pots needed! Brilliant for minimising transplant shock.
- Recycled Stuff: Yogurt pots, egg cartons (best for quick things!).
Seed-starting mix: Do not just dig up garden soil! It’s too heavy and full of potential problems. You need a seed-starting mix that’s light, sterile, and perfect for baby roots. You can find peat-free versions easily now.
Watering Can: Something with a fine spray so you don’t blast your tiny seeds away.
Labels: Non-negotiable! You will forget what’s what. Use lolly sticks, plastic tags, whatever. Write the variety and date with a permanent marker.
Plastic Covers: Clear lids or even cling film help keep humidity high for germination. Like a mini greenhouse!
Grow Lights: Okay, this is where people often stumble. A windowsill might work for some tough plants, but most seedlings will get tall and spindly (‘leggy’) without good light. Grow lights are your friend!
Heat Mat (Optional, but Recommended): Especially for tomatoes, peppers, chillies. Provides gentle warmth from underneath, speeding up germination like crazy. Makes a real difference for these heat-lovers.
Small Fan (Optional, but helpful): A gentle breeze helps prevent fungal issues and makes stems stronger.

Cucamelon seedlings developing true leaves in seed tray on grass. Plants are labelled with handwritten wooden markers.

Choosing Your Seeds: What Works Best Indoors?

Some plants really benefit from that indoor head start, while others are happier sown straight into the ground later on.

Great choices for indoors: Tomatoes, peppers, chillies, aubergines, brassicas (cabbage family), lettuce (for early crops), onions, leeks, basil, parsley, most annual flowers (marigolds, cosmos, zinnias etc.).
Better direct sown (usually): Root veg (carrots, beetroot – they hate root disturbance), beans, peas, corn, radishes, spinach.
Maybe start indoors (but late!): Courgettes, squash, cucumbers (grow fast, sulk if roots are messed with – start only 2-4 weeks before planting out).

Quick tip: Check the packet – it usually tells you the best approach!

Green tomato seedlings in container with dark soil.

How to Start Seeds Indoors

Alright, got your gear? Let’s plant some seeds!

Get Set Up: Clean space, clean pots, labels ready, seeds nearby.
Moisten Your Mix: Super important step! Tip your seed starting mix into a bucket or tub. Add warm water bit by bit and mix it up until it feels like a damp sponge (holds together when squeezed but isn’t dripping). Doing this before filling pots means even moisture.
Fill Your Pots/Trays: Loosely fill ’em up, tap gently to settle, then lightly firm the surface. Leave a little space (1-1.5 cm) at the top for watering.
Sow the Seeds: Check the packet for depth! Rule of thumb: plant seeds 2-3 times as deep as they are wide. Tiny seeds often just get pressed onto the surface. Sow 2-3 seeds per cell/pot – you’ll thin them out later, it’s just insurance!
Cover Lightly: Gently sprinkle more mix over the seeds to the right depth (unless they need light to germinate – the packet will say!). Pat down gently.
Water Gently: Use your mister or fine-rose can. Or, stand the pots/trays in shallow water for 15-30 mins (bottom watering) until the surface looks damp. Don’t wash your seeds away!
Label Immediately: Seriously, do it now before you forget which chilli is the super hot one! Variety and date sown.
Cover Up: Pop on the plastic dome or cover loosely with cling film/plastic bag. This keeps humidity high for sprouting.

Planting seed in peat pots and peat tablets.

Nurturing Your Seedlings

You’ve sown the seeds, now keep ’em happy!

Warmth

Put the covered trays somewhere warm. On top of the fridge works, but a heat mat is ideal, especially for peppers/tomatoes.

Light (The Moment They Sprout!)

Check daily! As soon as you see green, whip off the cover and get them under those grow lights immediately! This is when legginess happens if light is poor. Keep lights close (5-10cm) and raise them as the plants grow. 12-16 hours a day.

Watering

Keep the mix moist but not soggy. Think damp sponge. Let the very top slightly dry out between waterings. Bottom watering is great if you can. Try not to splash the leaves too much.

Thinning

Once seedlings have their first true leaves (the ones that look like the actual plant leaf, not the first baby ‘seed leaves’), pick the strongest one in each pot/cell. Snip the others off at soil level with scissors (don’t pull, it disturbs the winner’s roots!).

Air Flow

Once covers are off, good air movement is key. Open a window slightly (no icy draughts!) or use that small fan on low for a few hours daily. This helps prevent disease and builds stronger stems.

Feeding

Seed starting mix doesn’t have much food. Once the true leaves appear, start feeding weekly/bi-weekly with liquid seaweed feed or a balanced fertilizer, diluted to quarter or half strength. Don’t overdo it!

Pepper seedlings in a tray on the windowsill, growing seedlings, close-up.

Troubleshooting Common Seed Starting Problems

Even experienced gardeners hit snags. Here are the usual suspects:

Damping Off

What it looks like: Seedlings suddenly flop over at the base, looking pinched or mouldy.

What to do: Caused by fungus in damp, cool, stagnant air. Prevention is key: use sterile mix, don’t overwater, ensure air flow, clean pots well. Once it hits, affected seedlings are goners – remove them ASAP. I’ve definitely battled this one!

Leggy Seedlings

What it looks like: Tall, pale, weak, floppy stems.

What to do: They’re stretching for light! Get them under stronger light or move the lights closer immediately. A gentle fan breeze can help toughen them up too.

Nothing Sprouting

What it looks like: Just… soil.

What to do: Could be old seed, wrong temperature (too cold/hot), too wet/dry, planted too deep. Check seed viability, ensure correct warmth (heat mat), keep moisture consistent, double-check planting depth for next time.

Yellowing Leaves

What it looks like: Leaves losing their green colour.

What to do: Usually overwatering! Check the soil moisture first. Could also be underwatering, or if they’re older seedlings in tiny pots, they might need feeding or potting on.

Close-up of young seedlings growing in seed trays, representing new life and growth in a garden setting.

Hardening Off

Your seedlings have been living the sheltered life indoors. Chucking them straight outside is like sending a pampered poodle up a mountain – big shock! Hardening off gradually gets them used to sun, wind, and cooler temps over 7-14 days. Don’t skip this!

Day 1-2: Put them outside in a sheltered, shady spot for just an hour or two. Bring ’em back in.
Day 3-4: Few more hours outside, maybe a little gentle morning sun. Protect from strong wind.
Day 5-7: Gradually increase time and introduce more sun (still avoid harsh midday sun at first). Bring in at night.
Day 8-14: Leave them out longer, getting them used to more sun and breeze. If nights are mild (well above freezing), you can start leaving them out overnight in their sheltered spot towards the end.
Keep an Eye: If they look wilted or stressed, reduce the exposure. Make sure they don’t dry out!

Young roma beans sprouting in growing trays.

Planting Out

The big day! Last frost has passed, seedlings are tough thanks to hardening off. Time to plant!

Pick a calm, overcast day if possible (less stress).
Water the seedlings in their pots an hour before planting.
Dig your planting holes in the garden or fill your final containers. Add some compost!
Gently slide the seedling out. Plant it at the same depth it was in the pot (exception: tomatoes can go deeper!).
Fill the soil back in, firm gently, and water well. Done!

Basil seedlings in biodegradable pots on wooden table.

Conclusion

So, is starting seeds indoors a bit of effort? Yes. Is it complicated? Honestly, no. Once you have a simple setup and get the hang of the watering and light, it’s straightforward and so incredibly rewarding.

I remember my first tray of slightly wonky tomato seedlings – I was ridiculously proud! Seeing them grow and eventually eating fruit I’d nurtured from a tiny seed felt like a proper gardening achievement.

Don’t be intimidated! Start small with just a tray or two of something easy like cosmos or tomatoes. Give it a go, learn as you grow, and enjoy the process. Trust me, when you’re harvesting food or admiring flowers you grew from scratch, it feels amazing. Happy sowing!

How To Start Seeds Indoors (It’s Easier Than You Think!)

This post contains affiliate links. If you click on one of the links and make a purchase, I may receive a small commission at no additional cost to you. Read our affiliate disclosure here.