Seeds not germinating
Nothing comes up after the expected number of days. There are only five real reasons, and they are each testable.
What you see
The seed sits in the medium and nothing emerges after twice the expected germination time. For lettuce that is 20 days rather than 10; for parsley, eight weeks rather than four.
Sometimes the seed has rotted; sometimes it is still viable and simply waiting for a condition you have not provided.
Why it happens
Temperature
The most common cause and the easiest to fix. Lettuce refuses to germinate above 25 °C — it enters thermodormancy. Peppers and aubergines will not germinate below 20 °C. Parsley and coriander are slow at any temperature.
Old seed
Germination rate falls with age, and onion and parsley seed falls fast — under two years for onions. Seed kept somewhere warm and humid may be dead at one year.
Buried too deep
Lettuce needs light to germinate and should be surface-sown or barely covered. Anything more than a few millimetres stops it.
Too wet or too dry
Seed needs moisture to absorb but will rot in standing water. A medium that is soaked through and never dries is as bad as one that dried out completely.
Hard seed coats
Beans, peas and some others have coats that resist water. Usually fine fresh, but old seed may need chitting on damp paper first.
What to do
Test before you re-sow. Ten seeds on damp kitchen paper in a sealed bag, somewhere warm, for the number of days on the catalogue listing. Seven out of ten germinating means the seed is fine and the problem is conditions. Three out of ten means buy fresh seed.
- Match the temperature to the crop. Lettuce 18–21 °C, peppers 25–30 °C, parsley 18–22 °C and be patient.
- Surface-sow light-dependent seed — lettuce, celery, most herbs.
- Pre-soak large or hard seed overnight before sowing, but never leave beans or peas in water longer than that.
- Chit on paper if unsure — damp paper, sealed bag, warm place. You can see when the root emerges and then transfer to the pot.
Lettuce won't germinate above 25 °C — anyone beaten thermodormancy?
Tried the fridge trick and it worked, but is there a better way?
All problems
Six things go wrong in a small reservoir. The index covers each.