[Judd]

All of my toms (Gardeners delight,Sweet baby) are growing outside in straw bales.They are in a well sheltered place.there are approx 15 plants and they all have yellow leaves and don't look too healthy.
I'm going to try spraying them with Epsom salts and hope it works. It's my first year growing and it's sickened me a bit. Would it be safe to replace them with new plants from the garden centre?

[Ice]

It's a bit late to be replacing them.  What soil are they in?  Do you have any toms at all and are you feeding them?  A photo would be helpful.

[Judd]

They are growing in straw bales as I had seen this in a gardening mag and liked the idea.
I have been feeding them.
No toms yet and very few flowers.
I'll try to put on some pics tomorrow

[Ice]

Not come across this method before but a bit of research shows that there a lot of variables you need to get right.  Honestly, as a beginner I would get used to growing them traditionally before trying other methods just so you get a feel of the plants and what they like.

http://www.greenhousegrowing.co.uk/strawbale-growing-systems.html

[Plot74]

It may be a lack of nitrogen  usually starting at the bottom of the plant the leaves turn yellow then work up the plant.
John

[mumofstig]

we're always told that rotting material (in this case the straw) will rob nitrogen from the soil in order to rot down. So surely you would need a give them extra nitrogen, as plot74 says 

My 'Gardening Under Plastic' book says feed the bale with high nitrogen fertiliser twice a week 

[Judd]

I've sprayed them with Epsom salts and watered with tomato feed.
I'll get some Nitrogen feed and try that as well.
Thanks  for the replies