The planting coincides with the renewal of St Johns Hill's status as a green-gold Enviroschool.
Enviroschools was established with the aim to foster a generation of people who instinctively think and act sustainably.
The school celebrated last Friday with guests from Whanganui District and Horizons Regional councils as well as Department of Conservation staff who stayed on to help with the plantings after morning tea.
The celebration coincided with the Whanganui Resource Recovery Centre's Litter Free Lunch Day and the school has a goal for "100 per cent rubbish free lunch boxes" with the use of reusable wrap and containers.
New Zealand's first Arbour Day planting was on July 3, 1890 at Greytown in the Wairarapa.
The official date for Arbour Day is now June 5 and most New Zealand cities can trace their largest trees back to early Arbour Day plantings.