Decide what landscaping service you are looking for because different companies provide different services such as irrigation, lighting, design, and maintenance.
Once you decide the type of service you want you need to make sure the company can provide that service and that they have experience in that area of landscaping.
Look for testimonials from friends or family that currently have a landscaping company they are using.
Compare prices with the companies that you decide can provide a quality service you need.
Search the web for landscaping directories that list professional Landscaping services Houston.www.Ladco.co
Don't sign up for a long term contract, but to hire them for a month or so to make sure there service meets your standards.