The target of 5,000 has been achieved with the help of primary schools, youth groups and hundreds of members of the local community.
PECT has hosted tree planting and tree give away events over the past 18 months. It is part of the Forest for Peterborough campaign which aims to see more than 230,000 trees planted in and around the city by 2030.
LNER provided funding for the campaign through its annual Customer and Community Investment Fund (CCIF).
The fund supports projects and initiatives along the LNER route that address local issues and deliver educational or environmental benefits.
Anthony Pateyjohns, Head of Safety & Sustainability at LNER, said: "As a long-distance rail operator, we’re working hard to play our part in creating a greener future so we are delighted to be supporting Peterborough Environment City Trust in providing a boost to the environment in Peterborough, that will benefit both the local community and wildlife for years to come."
Tony Cook, Natural Environment Lead at PECT, said: "We are very grateful for the support LNER has given us in creating a Forest for Peterborough. It has been wonderful to see a wide cross-section of the community get involved in looking after the local environment. We’ve seen more and more volunteers joining us to play their part in Peterborough’s future. The legacy from LNER’s funding will be appreciated across the city for many generations to come."