More than 50 volunteers gathered at Cranford Basin in Mairehau to plant 1728 kahikatea saplings.
The event took place a day before Earth Day, which is dedicated to celebrate environmental protection around the world.
Planting organiser Donna Lusby from Conservation Volunteers New Zealand (CVNZ) said there was "an excellent turnout with amazing energy".
CVNZ is planning to plant 37,000 this winter, which the organisation says will be the biggest stand of the native tree in Canterbury since before Europeans arrived.
CVNZ volunteer Alice Bull said the event was a good way to "build connections to nature and community".
The event was in conjunction with One Tree Planted, an international organisation that has connected with groups in over 50 cities around the world to plant trees for Earth Month.
About 4100 trees had been planted before the event, with other planting days ahead.
The trees were supplied by Tree Planting Canterbury with funding from the One Billion Trees programme.
The land used for the tree planting is fertile land used for stormwater management to reduce the risk of flooding.