The fourth dimension is time - watching a garden change and grow into the picture that you imagined years before. Seeing in the little seedlings and saplings what they will one day become, is really one of the most satisfying things.
This can also be a frustration. In the beginning stages while plants are still small, and the garden is nothing like what it will become, it is difficult for the client to see the potential inherent in the design. At this point, it comes down to 2 things:
I have really tried to make an extra effort to give realistic expectations of the various stages, but sometimes when everything looks chaotic, its still necessary to reassure the client that in time it will begin to take shape and it really will look as you described!
This is where previous work can help to allay fears. A portfolio can do wonders. Before and after photos do a good job of giving realistic expectations.
Work that comes from referrals is usually fairly pain free, as a certain level of trust has already been assumed.