The contract, originally awarded in 2010, sees Blythe Valley provide a full range of arboricultural services to the city's non-highway tree stock.
Stakeholders who benefit from the services include the city's parks, housing, bereavement, transportation divisions, as well as allotments, education and economic development sites.
The contract extension also sees the area of work extended to cover the entire city boundary, in addition to a number of outlying properties.
Blythe Valley managing director Andy Hall commented: "Obviously, we are very pleased with the award of the extension, especially in what are challenging times for the council. We have been able to demonstrate understanding of and commitment to the council's objectives, which are in line with our own company values."
Other local authority clients of the company include Solihull, Redditch and Wychavon. It also provides services to the property management, construction and utilities sectors, as well as domestic customers.
Grounds maintenance contractor Quadron Services owns a 50 per cent share in Blythe Valley.