Are there any advantages in a opaque greenhouse?
What do you mean by an opaque greenhouse? You mean with shadings or whitened or painted with white sun block? Anyway, plants normally need > 5 celsius for the roots to grow. Your lower end is too low. And if it is completely opaque, nothing, except mushrooms will grow. They need light. The best thing to do is to experiment with as many different type of plants which you like to see how well they do. I suggest that it is probably worth starting (assuming you’re in the UK) around late April if you don’t get a lot of sun as the night temp will drop too low. Start your seeds in the house or a heated propagator and transfer to the greenhouse when the minimum temp is at least 5-6 celsius. Buy a min-max thermometer to check. You max temp is quite high and you may need to watch that your plants do not get scorched. I would try tomatoes, capsicum, cucumber (outdoor variety should do OK), spring onions, basil, and other herbs. You can use the GH as a coldframe to start off other crops, e.g. marr
