How can I perk up my tomatoes?

[Primrose]

I planted out my tomatoes under individual cloches a fortnight ago and at that time they were all nice healthy green plants, raring to go. Since then they all seem to have gone rather yellow and unhealthy looking. Could it have been the chilly nights or some deficiency in the soil? I dug home grown compost into the soil a while before planting - no treated grass cuttings in it or anything like that so wonder what I can do to get them looking healthy again?

[Beryl]

I did the same thing Primrose really because I wanted to get as much out as I can before I go away, but even though mine were under cover I lost about half to the cold nights. What has survived are beginning to pick up and hopefully now the weather is much warmer they will recover. Fortunately I had kept back some more plants in the greenhouse so could replace them. If you can't fingers crossed I think.

Beryl.

[Primrose]

I suspect cold night temperatures may be part of the problem. Think I'll have to treat myself to a Maximum/minimum thermomether which I can keep under one of these individual large mineral water bottle cloches so that I can see exactly what the lowest night temperature drops to.
It's partly my own fault. Even though I delayed sowing my tomatoes this year, I probably still sowed them a little too early and this dilemma of planting them outside and protecting them against low night temperatures would then be avoided.
However, I had dug in some chicken manure pellets into the soil around them and wondered whether at this stage of their early life the concentration of nutrients was a bit too much for the young plants to absorb.