The four are Rob Aspland, whose expertise is in the public and private realm, Charles Crawford, who works in the development, energy and infrastructure sectors, Ashley Dunseath, who is a specialist in development planning, public realm and also works internationally; and Mike Foster, who is responsible for development and regeneration.
This announcement comes on the back of "significant growth" according to senior partner Neil Mattinson and takes the partnership to 11 partners.
A successful half decade for the practice, has included its work on the London 2012 Olympic parklands and public realm which received massive international exposure, and winning the Landscape Institute Presidents Award in 2012.
The practice has also worked on the redevelopment of Battersea Power Station in London and the masterplan for a new Moscow park, Gorky Park, which won a highly commended Landscape Institute Award in November.
Last year it also won the Landscape Institute Strategic Landscaping Award for its line-side vegetation management strategy for Network Rail.
The multidisciplinary practice has seen particular growth in energy and infrastructure, solar energy projects, and development and regeneration, according to the company.
The practice has recently expanded its urban design and masterplanning offer, following the appointment of Vaughan Anderson as a director of this service.It is also now engaged in international projects, including work in the Middle East, Russia, China and India.