Mini cloches - Am I killing my plants with kindness?

[Primrose]

Because of lack of inside space to transfer into bigger pots, I've had to plant out some of my taller tomatoes into their final outdoor border and have covered them with the large 5 litre minteral water bottle cloches. They've been outside for about 10 days now. I'm noticing that some of the leaves are starting to look a little pale and developing 'rusty' patches. I wonder whether
a) The polythene is the guilty party by filtering out some of the light
b) The plants are suffering from lack of oxygen because of their
the enclosed environment. (There is a tiny ventilation space at the
top of the bottle which is slipped over the tomato stake up which it
will grow.

On really sunny days I've been removing the bottles for a few hours but wonder whether a carbon dioxide or other chemical build-up is affecting them.

[Johnboy]

Hi Primrose,
I think that your problem is night time temperatures. Although we have had some wonderful sunny days they have been accompanied by some very low night time temperatures and frosts. Tomatoes should never be subjected to temperatures of less than 10C and clearly most nights have been below this threshold.
JB.

[Primrose]

I did wonder about that myself but strangely, the tomato plants which I've been able to leave overnight in my mini plastic greenhouse up against the house wall don't seem to have been affected in the same way. Whether heat absorbed by the brickwork during daytime has meant that temperatures in here have remained slightly higher than the tomatoes under bottles against a south facing fence I don't know.

[Compo]

I think you are right Primrose after a warm sunny day the southfacing wall of my bungalow pumps out enough heat to sit by after dark and feel quite warmed, so I would imagine it would also warm anything put against it.