Good idea to turn your raised beds into mini greenhouses.
The popcorn corn will be really neat to do. I think I am going to put them in the greenhouse so that I will get some good ears. I really love popcorn. It is a comfort food for me too.
Yes start the grape seeds. I don't think it is too late. We are in May and most people will start seeds now. Give it a try. I have more seed so if it doesn't work I can send more.