The answer to 'retaining wall installation has weeds' is that weeds growing in a newly installed retaining wall are a common issue. This is often caused by improper soil preparation, inadequate drainage, or not using a landscape fabric barrier. Symptoms include weeds popping up between the wall blocks or at the base of the wall. To solve this, you'll need to address the root cause by improving soil conditions, enhancing drainage, and properly installing a weed barrier.
If the weeds are minor, you may be able to handle this as a DIY project. However, for more extensive weed issues or structural problems with the retaining wall, it's best to call in a professional landscaper. They can properly diagnose the problem, make any necessary repairs, and implement long-term solutions to prevent future weed growth.