yellow leaves

[lspittles]

This sounds like a real basic question but what causes leaves to go yellow? Several plants which were lovely and green in the potting shed are turning yellow since being planted out. Is it lack of a nutrient or trace element? Am I under/over watering? Do I need to be feeding the plants already?
I would appreciate some advice please. Thanks.

[TEB]

Yellowing can be nutrient deficiency, Epsom Salts can be applied for yellowing leaves, Chemist, GC and hardware shops should stock it.

[Snadger]

I just wonder whether you have hardened the plants off sufficiently before planting them from a warm, windless place, to a cool, wet, windy environment?