We typically try to do a couple or three layers. If you do a gentle sweeping bed, you may have some areas that have three layers, but other areas that only have one layer in the curve.
The plants that are going to be the largest 10 years from now should be the largest ones you put in the ground.
We see so many people who try their first stab at landscaping and end up wasting their money on the wrong things. They say, 'I can't afford professional help,' and they try to do it themselves. Then, when they realize they've made a mistake, they've already spent their money.
You want to have a layered look. You need a fairly wide, sweeping bed to allow for a low front row, a medium-height middle and a third row that is taller.