how much are you talking about raising? is it a 'fixed' bed or a natural bed? mulch [maybe on top of compost] might be the easiest answer - making sure that you don't smother the base of the plants. if it's a natural bed there's nothing that says it has to be the same level across the top of the bed

Do you mean "fixed" as in like a box? If so, yes, it's fixed. It should be at least 6" higher to be level with the edges. I wish I would have thought about the soil settling that much before planting. Live and learn.
thanks,
swilly

I know what you mean! It seems like the soil gets used up. I just dig up the plants and replant them after refilling the box to the new level. Obviously, you can't do that if the plants are too fragile to take that kind of treatment as in a nursery bed. I have one bed that I use just for nursery purposes and the level keeps going down and I will have to wait until most of the plants are moved to more permanent quarters to refill that box. My beds are 4 feet across and 6,8 or 12 feet long and filled with compost from my livestock. I don't till or agitate the soil in them but add layers to them sort of like lasagna beds.
spiderwoman

I had the same problem, but with a bed that had few large established plants yet. I stuck a shovel between the plants, formed a gap in the soil, and stuffed compost down as far as I could, sometimes even under the existing roots. This helped quite a bit, and now I just keep adding mulch on top. Perhaps if you do this just before a rain any roots that are damaged can quickly recover.

Ah, Andrea sort of a root feed and soil addition at the same time.