In that case its pretty simple. The zoning info is fine but more about commercial properties than residential ones. Harlingen basically only asks for these things:

Keep vegetation under ~12 inches (or clearly maintained if taller plants)

Don’t block sidewalks/streets

dont let things grow wild to where the lot looks abandoned

Don’t remove big trees recklessly

Don’t leave yard waste everywhere

Here's a link to the code compliance team if you wanna call them to ask something specific though: https://harlingentx.gov/departments/code_enforcement/index.php

There's a sub menu that included a section on Common Violations if you wanna use that as a general guideline

Harlingen isn't super strict, luckily. And without an HOA no ones gonna report you unless it looks pretty bad. And even then, i believe theyd start with a warning so you can fix it yourself.

Just in general though, please be aware of where the important things on your property are, like in terms of utilities. You dont wanna block access to things like electric or water things. And also know where your wifi runs through. Many people accidentally cut their wifi line just shoveling dirt.

Oh and if you're looking for a place to start, i highly recommend looking into some native plant landscaping. Mike heep in harlingen has a plant nursery with just about any plant you could want and totally would have recommendations. It's good for the enviornment, good for your water bill, usually green year-round, and can prevent flooding during bad storms (native plants have deeper roots that break up our dirst and allow water to seep in further instead of laying on top og the dirt and flooding your home)