I built a 12 inch raised garden bed with weed tarp at the bottom. (See also Raised garden in flood zone) I put the weed tarp in to prevent grass and other weeds from coming up from the ground. This has the negative effect of preventing roots from the plants I plant from going deeper than about 11 inches. Here is a photo:
What types of fruits, vegetables, and sunflowers will not do well in this setting due to their roots needing to go deeper?