The firm was tasked by the London Borough of Enfield to plant a 40ft Pin Oak tree to enhance an area of scrubland by a trunk road.
Weighing more than 10 tons, the tree was delivered on an arctic trailer and lifted into the ground with the assistance of an 85-ton crane.
It was planted as part of the Enfield Gateway initiative, which will provide funding for the redevelopment of key routes in and out of the borough.
Meanwhile, Gristwood & Toms has been awarded a £300,000-a-year contract with the London Borough of Bexley to manage the trees belonging to the borough's highways, parks, schools and cemeteries. The nine-year contract is subject to performance reviews.
Director Andy Toms said: "Tendering for new contracts is a complicated procedure and I'd like to congratulate all of the team here who have been involved in the process." Gristwood & Toms has committed to plant 750 new trees in the first three years.