The business manufactures composts and other growing media, and supplies large national retail outlets, landscapers, amenity companies and hobby gardeners.
Bord na Móna chief executive Mike Quinn said: "This acquisition helps support the sustainability of our retail horticulture business. Vitally, it will underpin Irish jobs and continued production across the group and within the broader horticulture business.
"Bringing White Moss on board provides Bord na Móna Horticulture with the opportunity to strengthen its position in the UK retail market. It also helps sustain the business into the future by delivering security of non-peat feedstock supply and a competitive supply chain model that drives value in operations and logistics."
White Moss employs 80 people at Formby and in Somerset. It mixes peat and green waste to make its products. It makes own label compost for retail chains as well as amenity compost.