Starting seeds indoors is genuinely one of the best decisions you can make if you're gardening on a balcony, patio or windowsill. You'll get far more variety than buying plug plants, spend a fraction of the cost, and have complete control over what grows. Spring is the perfect time to begin — most vegetables and herbs can be started now and will be ready to plant outside in May or June.
Light: The Foundation of Strong Seedlings
Light is the single most important thing for healthy seedlings. Most vegetables need at least 6 hours of direct sunlight daily. If your balcony faces south, you're in luck — you'll get the strongest light. North-facing spaces are trickier, but leafy greens and herbs like parsley and coriander will manage on 3–4 hours of sun.
If you're consistently getting less than 4 hours of direct light, or you're starting seeds indoors away from a window, a simple LED grow light makes an enormous difference. Position it 15–20cm above seedlings and run it for 14–16 hours daily. A seed starting tray with integrated LED lights is ideal for small spaces and costs under £30.
Containers and Compost — Start Cheap
You don't need to spend money on fancy seed trays. Yoghurt pots, egg cartons, and takeaway containers work perfectly — just drill or poke a few drainage holes in the base. Aim for containers about 5–7cm deep and 5cm wide for most seedlings. Label everything with a set of bamboo plant labels as you sow, otherwise you'll forget what's what.
For compost, use peat-free seed or potting mix — it drains better than garden soil and won't compact. Westland peat-free multi-purpose compost is widely available and reliable. If you want to stretch your budget further, mix it 50:50 with perlite or horticultural sand to improve drainage even more.
Watering — The Most Common Mistake
Overwatering kills more seedlings than anything else. The compost should feel moist but not waterlogged — imagine a wrung-out sponge. Check it daily. If the top feels dry, water gently. A fine mist spray bottle is perfect for seedlings; it gives you precise control and won't wash away tiny seeds.
Rainwater is better than tap water if you can collect it, but tap water is fine. Always water from below if possible — sit containers in a shallow tray of water and let them soak it up from the drainage holes. This keeps the stems dry and reduces fungal problems.
Common Problems and How to Fix Them
Leggy seedlings (tall and spindly) are reaching for light. Move them closer to a window or add a grow light 15cm above the leaves.
Yellow leaves usually mean overwatering. Check drainage immediately and let the compost dry out slightly between waterings.
Damping off (seedlings collapse at the base) happens in damp, stagnant air. Improve ventilation by opening a window nearby, and avoid overwatering.
Tiny pests like aphids occasionally appear on new growth. A strong spray of water usually does the job.
What to Start with
Don't try 20 different things your first year. Start with 2–3 types and scale up once you know what you're doing. Foolproof choices for beginners include tomatoes, basil, parsley, courgettes, and lettuce. A vegetable seed collection with multiple varieties gives you variety without the commitment.
Sow seeds 4–6 weeks before your expected outdoor planting date (late May in most of the UK). Most seeds germinate in 7–14 days. Once seedlings have their first true leaves (the second set to appear), thin them out so they're not crowded. Crowded seedlings compete for light and air, and they'll be weaker when you plant them out.
Hardening Off Before Planting Out
About 2 weeks before moving seedlings outdoors, start exposing them to outside conditions gradually. Put them outside in a sheltered spot for an hour on day one, then gradually increase exposure over 7–10 days. This hardens them off so they won't wilt when planted permanently. It sounds fussy but it genuinely works.
Start small, keep things simple, and you'll have strong, healthy seedlings ready to grow. Once you've done it once, you'll wonder why you ever bought plug plants.