Germination: warmth, moisture, light and depth
Germination is a seed waking up. Inside every seed is a tiny plant with a store of energy, waiting for the right signal. Give it what it needs and it sprouts. Get one thing wrong and even good seed sits and sulks.
What every seed needs
What | What it should be |
|---|---|
Moisture | evenly damp, never dry or soaked |
Warmth | 18–22 °C for most seeds |
Air | loose, free-draining seed compost |
Light | some seeds need it — check the packet |
Moisture softens the seed coat and triggers growth. The compost must stay evenly damp from sowing until the seedling appears; a clear lid or bag helps.
Warmth is the engine. Most seeds germinate fastest at 18–22 °C, which is why a warm windowsill or a propagator beats a cold sill.
Air matters too. Seeds breathe, so use a light, free-draining seed compost rather than dense, waterlogged soil.
Light is needed by some seeds to germinate, and those are left uncovered. The packet tells you when that applies.
Step by step
- Fill your pot or tray with seed compost and firm it lightly.
- Sow as deep as the seed is wide — leave light-loving seeds on the surface.
- Water gently, or stand the pot in a little water so it draws up from below.
- Cover with a lid or bag to hold the moisture in.
- Keep the compost at 18–22 °C.
- Take the cover off the moment the first shoots appear.
Once they are up, give them as much light as you can. That is the difference between stocky seedlings and long, weak ones.
How long does germination take?
It varies a lot. Fast crops such as radish, beans and many leaves are up in 3 to 7 days. Peppers, parsley and some perennials take two to three weeks or more. Check the germination time on your packet before you worry.
Speeding it up
- Give bottom heat with a propagator or heat mat, holding the compost at 18–22 °C.
- Cover to trap humidity.
- Pre-soak large or hard-coated seeds overnight: peas, beans, sweet peas and beetroot.
- Use fresh seed compost — fine and free-draining beats old, lumpy mixes.
- Sow in season. The right warmth and light beat any gadget.
Common mistakes
- Letting the compost dry out. Once can be enough to stop germination.
- Sowing too deep. Small seeds need only a dusting.
- Too cold. A chilly room slows everything down.
- Burying light-loving seeds. Some need to sit on the surface.
- Giving up too soon. Check the packet time first.
Frequently asked questions
Do seeds need light to germinate? Most do not and can be covered. Some, such as lettuce and snapdragons, do. The packet will say.
Should I soak seeds before sowing? Only large or hard-coated seeds really benefit. Most small seeds do not need it.
What temperature is best? Around 18–22 °C for most seeds. A few warmth-lovers such as chillies prefer a little more.
The full version of this guide is on seedschoice.com.
Ready to sow? What you can sow now
- Vegetables you can sow this month
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- Vegetables to sow directly outdoors
- Fast-growing vegetables — quick results, ideal for beginners
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Updated on: 05/10/2026
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