In doing a run through of the site, we've touched on the major seo issues, but in terms of usability and other things you might want to look at...
The overall design looks good, but white text, especially in volume, can become a tiring/difficult read when there is a stark, black background.
The photography is amazing. Love seeing business owners recognize that everyone here works in a visual medium and the site pics should be taken seriously and reflect this reality. With your gallery, I would add context or details to what each pic shows. The customers might find it useful, and the engines will like the additional content.
The home page has it's text content center justified. For anything more than a sentence or two, it becomes an odd read. We "naturally" read left to right, content that is left justified. From a continuity standpoint, the rest of your site is left justified.
On the "how much does a new lighting system cost?" and "we repair systems..." images on the home page, I would add a hover interaction, such as a border color change, so that people don't miss that these are actually links. I don't think I saw any other navigational images on the site, and I missed them twice because I wasn't looking at them in that regard.
a guy who knows both the lawn business and web strategy