Congressional offices receive an astounding amount of unsolicited material.
By making it relevant, short, and easy for the staff person to keep. You should be able to boil the essence of your materials down to one page. You may want to include a few pages of background material with your main message, but do not leave behind reams of paper. The better thing to do is to let staff know what kind of resources you have available on landscape architecture on a particular issue should they need them. If some of the information you would otherwise provide can be accessed on the web, give them a sheet with the web site address and a table of contents.