Writing as both a landscape architect and civil engineer, I concur with the guidance to hire a landscape architect.
I encourage your efforts to expand your practice but believing that you can gain the knowledge of a landscape architect (or horticulturist) from an introductory text on landscape architecture is analogous to believing that a landscape architect could practice engineering from reading an introductory text on engineering.
Work with a landscape architect to learn the information from them. Most will be happy to share and you will probably find that your projects benefit in other ways from their participation. They will also be able to direct you to other resources and continuing education courses that they are required to take and in which you may find the guidance you seek.
The specific information that you seek is found in the areas of planting design and horticulture. Plants come in all shapes, sizes, conditions, etc. It takes time, experience, and research to know what works best where, how large it will get, what its pros and cons may be, and so forth. Join your local botanical gardens or arboretum and spend some time getting familiar with those sites. The folks that work there are a wealth of information!
In any case, specify native plants. Pay attention to sun/shade requirements, mature plant size, plant spacing, water requirements, soil pH, etc. Natives will be better adapted to the climate of your region, better support local fauna, and require less maintenance. You may be able to find continuing education courses on the desired topics through your local agricultural university (e.g. Texas A&M, NC State, etc.) and ag-extension programs.
Good luck!
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Tony Hauser, PLA, PE
Wood Environment & Infrastructure Solutions, Inc.
Asheville NC
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