"Rupert (W.Yorkshire)" wrote in reply:

Depending on which seeds, 50% may be considered a spectacular success.
Which seeds?
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Now retired, having been a gardener for many years, I should know when and
how to sow seeds in the right soil and conditions. You may consider,
depending on which seeds, a germination of 50% is a spectacular success,
I don't. The seeds were supplied by a reputable company that should make
sure its suppliers are not delivering duff seeds. After discussing the
matter with colleagues, I was not surprised to learn that they too have had
trouble with non germinating seeds, more so in recent years. In the open
garden this could be put down to climatic conditions at the time of sowing,
but not in heated greenhouses.The non germinating seeds include, lettuce,
spring onion, 'Stargazer'dahlia, coleus, runner beans, chilli and tomato.
For the second year running I have had the most success with radishes,
even our resident four wood pigeons won't touch them.

MCT