You'll want an early short variety (like Swift or Lark) given how far north you are, they can be spaced at about 10" or so..... If you can spring for a big fleece cloche they'll like the protection early on and they want to be in a block not a row otherwise your pollinaiton will be erratic... also it's generally good practice to give different varieties some seperation, especially if you grow modern F1 types...
chrisc