I've read the garden article on this, but it doesn't give me the info I need. There's probably a few discussions on this but a search doesn't bring them up. I never have much success, they seem to start off ok in a deep seed tray (10 cm deep) in my unheated greenhouse, but they never thicken up to pencil width, I always end up planting them out quite skinny 3-4 mm. Consequently my leeks are nowhere near as thick as OPs down the plot (2-2.5 cm). Any advice to get them to grow thicker before planting them out. They were planted in March, then down to the plot early August. This has happened two years running, so I'm doing something wrong, just not sure what. Thanks for any help on this.