Sowing in plug trays

I have often wondered how the nurseries sow and sell the small plug plants as I would like to do the same with veg but the seedlings grow leggy, do they prick them out into the plug trays or sow and leave them in.

 

Magic and sorcery No, I really have no idea.. I assume they're under special growing conditions with controlled lights.. I'd like to know this too. Hope someone can answer you

 

They fill the trays with compost automatically, then another machine plants the required number of seeds per plug, generally one for vegetables, then they are kept warm until they germinate, then given any extra lighting required, at this time of year little extra lighting will be required for outdoor vegetables, fed and watered not much warmth is needed by now and given good ventilation. Any plugs with no germination are popped out and replaced with spares to fill the tray.
At home fill plug tray manually, sow two seeds per plug,(thin at first properleaf stage) keep in a greenhouse or cold frame until ready for planting out then harden off and plant out. Curse at plugs with no plants.
If you want leeks or brassica plants to sell probably better off the old fashioned way sow fairly thickly in a in a nursery bed then feed and water as required until desired size is reached.

 

Thank you for an interesting answer to all that responded, I have always wondered.