[Yana]

I've got a load of seedlings in the greenhouse (mainly brassica) along with leeks that have been transplanted in bunches in to paper cups ( worked a treat like this last year) and have been covering them up when the forecast is for a cold temperature over night. Also got some peas that have sprouted.
My query is this......
The fleece that I use isn't that thick stuff, so I have it double and seems to have worked so far. The next few days are predicting day time temps of little over freezing and night time temps to fall well below so is it OK if I leave the fleece on all day?
I'm concerned that there won't be enough light getting to the seedlings and they will go leggy.

[DD.]

Your greenhouse will warm up quite a bit during the day, well above the outside temperature.

This is called, errr... the greenhouse effect. It's essentially light being converted into heat when it strikes solid objects and then being trapped inside by the glass. This does not have to be direct sunlight.

If it's above zero outside, it will be well above it inside and you can safely remove the fleece.

Of course, this does not happen at night, hence the temperature in a greenhouse overnight will fall to close to the ambient temperature, unless you have some form of heating.

[JayG]

Agree with DD, especially as the plants you mention are relatively hardy.

In general though, don't expect fleece to perform miracles - small pots and seed trays have very low mass so don't have much stored heat to preserve (a max-min thermometer is a useful tool to monitor what's going on in your greenhouse, preferably not just for providing evidence at the post-mortem - be cautious with more tender plants, especially at the seedling stage.)

[Yana]

I do have a max/min thermometer and use is regularly just wasn't sure about the whole fleece issue.