I discovered that the reason I’ve been staring at a completely empty tray of marigolds is that the seed was from 2023, which is too old for marigolds. I’ve resown the whole tray with new seed today and put it on the warm hall floor.
Various holes in the sunflower, gourd and nasturtium trays have been resown too. Those trays are in the conservatory. In the office I’ve nipped the tops off my terrible sweet peas and I’ll direct sow others at the weekend.