I'm a proponent of QR Codes, but I don't think you'll see much use on your trailer. Yards signs, however, are a completely different story. I love them for yard signs.
You have a crisp, clean branding image and decluttering by losing the QR would allow you to center the phone and web address. I'm not a fan of the social links, and would prefer to funnel them to and then out from your web site. Facebook is obviously more usable than not, but do you want to present 4 point of contact options on a trailer door? With Twitter, I would only go through the permanency of lettering it if you know you will absolutely utilize it. If someone takes the time to hit your Twitter page and sees, "Well, looks like a good day to mow!" and it's from 4 months ago, their time has been wasted, no matter how little time you perceive it may be. Decluttering also allows you to maintain a visual focus for the eyeballs.
a guy who knows both the lawn business and web strategy