Cranswick Pet Products supplies label and own brand products to Tesco and Pets at Home and other retailers, but not garden centres.
This investment follows Westland's launch into the wild bird market with 'Peckish'.
Westland said joining Cranswick Pet Products and its brands including Bucktons and Nature’s Feast will give it access to market leading knowledge, expertise, infrastructure and world leading manufacturing facilities, at Driffield in East Yorkshire.
Westland will now have four main product categories: birdcare, growing media, fertilisers and chemicals and seed.
Edward Conroy, joint managing director of Westland said:
"Both Westland and Cranswick Pet Products have a strong record in growing categories, delivering innovation and consumer quality. It is these synergies that make this one of the most exciting opportunities in gardening.
"The purchase of Cranswick Pet Products is the perfect complement to our existing business and reinforces our strategy to keep driving participation in gardening by delivering unique products to make the garden a more enjoyable environment. A key reason for Westland to invest in Cranswick was the knowledge and the commitment of the senior management team as well as its high quality workforce."
Sam Marriage, national sales manager of Cranswick Pet Products said:
"We are incredibly excited with the new opportunity to merge with Westland. We are confident that together as one we can grow the market and communicate the benefits of quality bird food, which will increase the number of birds in the garden and will give gardeners great enjoyment."
Davy Corporate Finance acted as lead advisor to Westland Horticulture on this transaction.