I mix and match plants all the time in my raised beds, if there is space to add some thing well it get added. I currently have onion,broccoli,strawberry,and lettuce all in the same bed! they are doing great. also have asparagus,collards and spinach together in a bed, then there are the potatoes carrots and tomatoes in the other raised bed, how about potatoes,corn and squash together too. they like being all mixed up and in some cases it helps to confuse the bad bugs or chase them away. I tend to just wing it and fill in open spots with what ever I think will work there.