Well, I actually have never grown outside, But in my yard I always work in some sand and peat moss, about 2 parts soil, 2 parts peat moss and 1 part sand.
Basically you want to keep the soil from becoming to compact (sand) and sometheng to retain moisture (peat).

If you ssearch enough there was a couple good threads about outdoor grows about 2-3 months ago, or one the experts on here will chime in.......good luck to ya.