First of all, I have to say what a great idea to post and get feedback from installers before you go off into the real world and do it! I wish every landscape architect was so open minded and forward thinking! Thank you!
In our state, probably like a lot of states, there are either landscape architects or landscape designers. The former are usually used on larger residential landscaping projects (e.g. $100K and up) and for commercial projects and the latter are for mid sized to larger residential projects. And of course, L.A.s have to be certified and designers do not. That's how it works around here.
Because we do just residential landscapes and only a small % of our work are the really large resi. jobs, I deal mostly with landscape designers. Although we do work with a local landscape architect occasionally. And I've installed several jobs that were designed by L.A.'s over the years.
Some of my issues with L.A.s are the very same issues I have with landscape designers. Some are more specific just to L.A.s. only.
So one problem that I have with both designers and L.A.'s is the lack of LOCAL product knowledge. In my opinion, if you're getting paid big bucks to design landscapes, you should know all of the local products that are available for landscapes BETTER than the installers do. You should know every paver that is available locally; every kind of SRW; every variety of seat wall or courtyard wall that is available; be very familiar with several of the main brands of outdoor lighting that are available locally; know which plants are fairly common and easy to find; and which ones are almost never available; know what SIZES of plants and trees are common in the area (so you don't specify sizes that are impossible to find); learn what common methods are used in the area for steps up hillsides; learn what kind of rock is available locally; etc. Constantly browse through websites of the top landscape contractors in your area to watch for trends, products and materials they commonly use, etc. Go buy local suppliers, rock yards, hardscape suppliers, pond distributors, etc. and keep up on new materials, innovations, available products.
The only other thing is that if you don't know exactly the right product to chose for a certain area, leave it to the contractor to chose. Nothing wrong with that. I'd rather you leave me to decide what product to create a nice seat wall out of rather than you specifying something I've never used, don't know how to work with, or is extremely difficult to get.
One of the things I often see L.A.s do is specify stuff that looks cool on paper but is not really very easy to do or maybe next to impossible to do in reality. They have no clue how to actually accomplish what they designed. They just think it would look cool. Don't do that! If you have an idea, help me figure out what product to use to make that idea happen. Don't just leave me to dream up some way to make it work.
I could write a lot more but I gotta get back to work....