[amiman]

We have a green polytunnel on our plot, second year.
We have started from seed swede and cabbage all growing but the plants are very leggy is this because of the green cover? I have read that seedling can get leggy looking for the light.

The shoots are a good 2 inch (25mm) before the leaves, but our lettuce is fine not leggy at all.

Any ideas

[mumofstig]

They're leggy because they don't like being hot in there, at this time of year..... brassicas should be outside, as soon as they've germinated if you do really need to start them inside, at all.
The amount of green in the cover doesn't restrict light enough to bother anything, but the plastic keeps all the heat inside, good for things like tomatoes and peppers - but can be deadly for others.

[al78]

I need to start brassicas indoors even at this time of year, because otherwise I would be giving the slugs a free buffet. Once they have germinated I do put the seed trays outside in a well ventilated cloche greenhouse (to keep flying nasties off them).

Yes the cover is causing legginess, not because of light suppression, but because the sun is strong, and the cover is preventing convection. Convection is a cooling process (it transfers heat from the ground to the atmosphere) and like a greenhouse, there is the danger that with inadequate ventilation, you effectively have a big convection oven, and you end up dry roasting your crops. It is a similar process what generates extreme temperatures in Death Valley California (https://medium.com/@erinwinick/why-is-death-valley-so-hot-18495df18762).

[amiman]

OK thanks for your answers.
We have planted them out burying the leggy bit aswell, I read somewhere you can do that. But just in case we have potted some more seeds and will plant out quicker.

Thanks again for taking the time to answer