I do some raised beds too, they work great. I use homemade compost, mostly, but sometimes if I don't have enough I'll buy. I usually buy something labeled "humus" or "aged manure" to mix in. I don't buy "top soil" or "garden soil" becoz I don't think it has enough nutrients in it. I don't buy potting soil becoz it's too expensive. If you prepare raised beds in advance, like prepare in the fall and plant in March, you can do 'lasagna gardening' which is to cover the bed area with wet newspaper or cardboard and layer any and all organic matter like 18-24 inches deep, leaves etc, and it will "cook" down by springtime to about 6-12 inches. (you can google lasagna gardens and get lots of info on raised beds that way). When I lived in N.O. we planted out after St. Patrick's Day, or some said St. Joseph's Day, which is March 17 and 19, as I'm sure you know. Hope this helps you some. I've never grown cukes, but I guess you need something for them to grow up on or to sprawl out.