I'm in MN - which has been having very similar weather. The plants have managed to grow OK in spite of that here... If they grew OK in the same spot last year, I'm guessing they are getting enough sun. Same seeds as last year?
The mix you use sounds maybe a little light in the nutrients. If the manure wasn't already composted manure, then it needs to compost before the plants can use it for food. Is there a university or something nearby that you could bring in a soil sample (or 8) in to for testing? That should give you clear answers on the mix you used.
