wide mouth canning jars upside down over the plants can save them from a frost. Do you have any large glass bowls, like a punch bowl, or a large glass mixing bowl? Those can be turned upside down over some plants like chard & the Buttercrunch or Romaine type lettuces to keep them growing thru the winter. I live in Utah now, & grew lettuce all last winter under glass cloches. I used the domes from cake plates & cheese plates, that I bought at yard sales for pennies.