What you can do
Millennials demand fast, reliable service. Responding to customer inquiries as quickly as possible must become a priority. If you have a "contact us" feature on your website, you have to check email every day and/or night and respond promptly.
Speaking of websites, you better have a nice one these days.
Get involved in your community with donations, special projects, educational efforts, etc. This scores big points with Millennials—so be sure to get involved, and then promote your community outreach.
Millennials respond well to group involvement. Consider programs such as referrals clubs and loyalty incentives. Testimonials are as important as ever. In addition to the standard written testimonials, talk to your happy customers about doing video testimonials which you can post on your website and social media pages.
Speaking of social media, this is where Millennials are—so you have to be there too. Many contractors have established successful Facebook pages. Twitter accounts are a close second. LinkedIn also can come into play. YouTube channels are underutilized by landscape contractors. Consider all of these approaches.
Most importantly, maintain a consistent message. Inconsistency in message, reliability and overall professionalism will lose the trust of a Millennial. Millennials do like the "sizzle," but it can't overshadow the "steak."