Leggy, weak seedlings
Leggy seedlings are tall, pale and thin, with a long bare stem and a big gap between the seed leaves and the compost. They are stretching towards the light. It is the most common thing to go wrong indoors, and usually fixable.
How to recognise it
Sign | What it looks like |
|---|---|
Tall and thin | long, weak stems |
Pale | light green or yellowish |
Floppy | leaning or falling over |
Big gaps | stretched between the leaves |
What causes it
- Too little light. By far the main cause. On a dim windowsill seedlings stretch towards the nearest light.
- Too much warmth. Heat without matching bright light pushes fast, soft, weak growth.
- Overcrowding. Seedlings packed together shade each other and race upward.
- Sown too early. Sowing weeks before there is enough natural light means a long, leggy wait indoors.
- Light from one side only. Without turning, seedlings lean and stretch towards the single window.
How to rescue them
Act early and they can usually be saved.
- Move them to the brightest spot you have, or add a grow light a few centimetres above them.
- Lower the temperature a little. Cooler and brighter grows stockier plants.
- Add airflow with a gentle fan. Moving air thickens and strengthens stems.
- Thin or space crowded seedlings so each gets full light.
- With tomatoes you can pot on deeper: bury the long stem up to the seed leaves and it will root along its length.
Can they still come good?
Often, yes, especially if you catch it early. Tomatoes recover well precisely because you can bury the stem. Most others — herbs and brassicas, for instance — cannot be buried deeper, so improve their light and airflow straight away and they usually firm up. Badly stretched, floppy seedlings are often quicker to re-sow. With fast crops you lose very little time.
Preventing it next time
What | How |
|---|---|
Bright light | from day one |
Cooler nights | do not keep them too warm |
Sow on time | not too early |
Sow thinly | room to grow |
Turn daily | even light |
Airflow | strong stems |
The fix is almost always more light and less heat.
Frequently asked questions
Will leggy seedlings still grow? Many will, but they are weaker and more prone to flopping or disease. It is worth fixing the cause now.
Can I plant them deeper? With tomatoes yes, with most others no — improve their light and airflow instead.
Do I need a grow light? Not always, but on a dark windowsill a simple grow light makes a big difference.
Why are mine leggy on a sunny windowsill? Light from one side combined with indoor warmth. Turn them daily, cool them down and add airflow.
The full version of this guide is on seedschoice.com.
Starting again? These seeds are easy
- Fast-growing vegetables — quick results, ideal for beginners
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- Vegetables you can sow this month
- All vegetable seeds A–Z
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Updated on: 05/10/2026
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