The partnership, which represents the four boroughs of Croydon, Kingston, Merton and Sutton and was established to save £32m by clubbing together as one client, awarded the work as part of a larger environmental services contract, which started this week.
Veolia won the £209m, eight-year recycling and rubbish collection contract, which will see it deliver services to the four boroughs and one million people. The contract formally began on 1 April but Veolia started work yesterday.
Idverde won the second lot in the environmental services contract, and will provide grounds maintenance to Merton and Sutton under the new contract. It already holds contracts with Kingston and Croydon to provide their grounds maintenance. The new contract started in February but the win was not announced by the client until now.
Idverde has taken on 89 staff through the TUPE process. Grounds maintenance was previously provided in-house by both councils.
The tender was controversial when proposed in 2014, because it lumped in parks services with waste. The concern was that a facilities management or waste disposal company with little horticultural expertise would win the whole contract.
Idverde UK chief executive Nick Temple-Heald said he was glad a horticultural specialist had been chosen after "a rigorous and challenging procurement process".
"We are incredibly pleased and proud to be providing parks, grounds and cemeteries maintenance services across Merton and Sutton and welcome our new employees, who join idverde colleagues already providing these services in Kingston and Croydon.
"With Veolia and idverde, the specialists in their respective fields, now delivering services across all four boroughs this procurement really has resulted in the best of both worlds for the residents of south London."
Chair of the South London Waste Partnership joint committee Phil Doyle said: "These new contracts will deliver high-quality services and save tens of millions of pounds – well in excess of the £30m savings target that was set. Working together, the four boroughs have negotiated excellent deals with two commercial partners who bring huge experience and expertise to the table.
"When we started out on this procurement in 2015, there were some who doubted we would ever get to this point. Recycling and rubbish collection in particular is such a sensitive and difficult service to be re-designing. Doing this across four London boroughs, with three different political parties in power, was seen by some as too difficult.
"But the four boroughs of the South London Waste Partnership have once again worked together in an effective and business-like manner. This sort of cross-party, cross-boundary working is going to have to become the norm if we are to achieve the more harmonised approach to waste collections that regional and national government are advocating. The South London Waste Partnership has shown that it can be done."
This week, idverde also started work in the north London borough of Camden, where it won a five-year grounds maintenance contract with a focus on increasing volunteering and naturalistic and nature-friendly planting.