my mother has her raised beds filled with pure compost and does well with most veggies like tomatoes and cukes, but her peppers dont seem to thrive like the others small/few pods. might be too much N or a ph issue. i put 6-8" ontop of my garden in the fall and till in the spring. i'm guessin you access to plenty of sand, might try mixing at different ratios and see how it works.