Seeds Not Germinating UK
Sown seeds that won't sprout? This guide covers every common cause of poor germination in UK conditions — and exactly how to fix each one.
Growing advice verified against RHS guidance by the SoilCommander Growing Team.
Minimum Soil Temperatures by Crop
| Crop | Min soil temp | Ideal soil temp |
|---|---|---|
| Carrots, parsnips | 7°C | 12–18°C |
| Peas, broad beans | 5°C | 10–15°C |
| Lettuce, spinach | 5°C | 10–18°C |
| Courgettes, beans (French/runner) | 12°C | 18–21°C |
| Tomatoes, peppers, aubergines | 18°C | 21–25°C |
| Cucumbers, sweetcorn | 15°C | 20–25°C |
Top Causes and Fixes
1. Soil or Compost Too Cold
The most common cause. Seeds sown in outdoor soil below 7°C (for most crops) will rot rather than germinate. Warm-season crops like tomatoes need 18°C+ and must be started indoors with a heated propagator. Use a soil thermometer before direct sowing in spring.
2. Old Seed
Parsnip and onion seed is only reliably viable for 1–2 years. Most other vegetable seeds last 3–5 years if stored correctly. Always check the sow-by date on the packet. Store seed in sealed containers in a cool, dark, dry place.
3. Sown Too Deep
Fine seeds (carrots, lettuce, celery) must be sown at 2–5mm depth. Deeper and the seedling runs out of energy before reaching light. Always follow packet depth instructions; some seeds (celery, lettuce in summer) need light to germinate and must be pressed onto the surface without covering.
4. Compost Too Dry or Too Wet
Seeds need consistent moisture — compost should feel like a wrung-out sponge. Dry compost prevents germination; waterlogged compost causes rot. Cover seed trays with a lid or cling film to maintain moisture; remove as soon as seedlings appear.
5. Damping Off
Seedlings emerge then collapse at the base. Caused by fungal pathogens in overwatered, poorly ventilated conditions. Use fresh, sterile compost; water from below (sit tray in water briefly); ensure air circulation around seedlings; don't overcrowd.
6. Light Requirements Not Met
A few seeds need light to germinate and must not be covered — celery, lettuce (in summer) and some herbs. Check the packet: if it says 'surface sow' or 'do not cover', press the seed onto moist compost and leave it exposed. Covering these seeds is a common reason they fail to appear.
Common Mistakes to Avoid
- Using old or home-made compost for seed sowing. The RHS notes old or home-made composts can give unreliable germination and more disease problems than a fresh, peat-free seed compost.
- Leaving seedlings uncovered against birds, slugs and mice. Each threatens seedlings differently and needs its own protection — mesh or cloches for birds, barriers or nematodes for slugs, traps for mice.
- Skipping thinning once seedlings emerge. Overcrowded seedlings compete for water, nutrients and light, which hinders growth even when the original sowing itself went perfectly.
Frequently Asked Questions
Can I resow if my seeds fail to come up?
Yes — the RHS notes that resowing within about two weeks of a failed sowing keeps most crops on track for the season.
Does the quality of compost affect germination?
Yes — old or home-made composts can cause unreliable germination and more disease problems than a fresh, peat-free seed compost.
What eats seedlings right after they germinate?
Birds, slugs, snails and mice all target new seedlings, and each needs a different form of protection, from mesh and cloches to barriers and traps.
See all growing guides: UK vegetable growing guides · Garden Problems UK · UK vegetable planting calendar
Last updated 4 July 2026
Helpful Next Steps
Use these practical links to turn the guide into a clear garden plan and the right next action.
Plan the next step
Use the printable UK Vegetable Garden Planner to turn this guide into sowing dates, bed layouts, and weekly garden tasks.