We have broccoli growing in our winter garden for the first time. How cold can broccoli take it? We have covers and insulation and can do what's necessary but I don't want to do more than is necessary since it shares a bed with kale, parsley, and spinach. The lettuces and Chinese cabbage are in other beds and we try to protect them from below 25 degrees (also mesclun mixes), although I think they could take it a little colder. I don't want to stress any of the plants. Thank you.