Julie Mutton, an assurance and business services partner, and Paul Duckworth, a tax partner, from the Southampton practice of Smith & Williamson, lead the work.
Sharmini Martin, Briers' finance director, said: "Smith & Williamson has a reputation for working with ambitious companies and entrepreneurs. This is a really good fit for us and we looking forward to working together. Customer demand continues to grow and we've added more than 220 new products for 2016.
"With expansion, through own-brand and licensed products, comes extra financial responsibility - Julie, Paul and their colleagues at Smith & Williamson have the expertise and credentials to help take our trusted brand to the next level."
Mutton said: "Briers was looking for a firm with a great reputation for building long-term relationships with their clients, as well as the ability to create solutions when looking at all aspects of the company's finances."
"Briers is looking to develop its product range for stockists, such as retailers and garden centres. We'll be stepping into Briers' financial shoes to help the independent retailer take the next step in growth."