It took me a moment to remember what courgettes are. Here we call them zucchinis. :)

I don't know why your seeds didn't germinate. Zucchini needs warmth to germinate but if you're comfortable, they should be too. One would assume it wasn't a problem with the seeds as one did germinate.

As for the chard and lettuce, they prefer much cooler temps to germinate and grow than zucchini.

I recall when I 1st started gardening and I planted 4 zucchini plants. I thought they were going to take over the world! The plants sprawled all over the place and they had way more zucchinis than we could eat. The neighbors started to run when they saw me coming. So it may be a heaven send that only one germinated, lol!

Btw, there's a vegetable gardening forum here at GW. You'd probably get more responses to your query there. This forum is fairly quite most of the time.

Come on over!