"I am pretty sure it will grow up to be a big, strong tree."
Mr Rieger said the idea to plant the trees in honour of his son was raised by Spirit of Adventure Trust voyage co-ordinator Rachael Mitchell.
Hamish Rieger boarded the Spirit of New Zealand sailing ship on August 3-12, 2015, as part of a youth development programme.
In an effort to give back to the community and the Spirit of Adventure Trust, Donna and Greg Rieger are completing 12 half marathons in 12 months to raise funds for the "I Ride With Hame" project which creates scholarships for the trust.
The Spirit of New Zealand was planned to arrive in Tauranga as part of the Mount Joggers and Walkers Half-Marathon on Sunday, June 4. But 50-knot winds stopped the ship from making the voyage from Auckland to Tauranga.
"The Tindall Foundation donates so many thousand trees every year for Arbor Day. They suggested the Spirit plant some trees," Mr Rieger said.
"As the boat was going to be here, regrettably it did not make it, it would have been fantastic to have had the cadets plant some trees for Hamish."
Mr Rieger said he made a quick call to the Tauranga City Council, which allowed planting of the trees. Council supplied the three pohutukawa trees which have been planted on the island.
"I was completely blown away when I got the call to say it was going ahead and they would give us the three trees. Thank you so much," Mr Rieger said.
"So it is not only under Hamish's name but under the Spirit of Adventure Trust."
Tauranga City Council parks asset co-ordinator Dave Grimmer said the three trees would grow to be the biggest trees on Leisure Island.
"This is all remnants of a coastal pohutukawa forest, so they will be the specimen trees out here on Moturiki."
Spirit of Adventure voyage co-ordinator Rachael Mitchell said the tree planting was also part of Project Crimson, which was established to restore pohutukawa and rata trees to New Zealand's forests and coastlines.
For more information, visit projectcrimson.org.nz
To support the I Ride With Hame fundraiser, donate direct to ASB 12-3011-0461607-52. All funds go towards the Spirit of Adventure Trust.
To join the Riegers on any of the half-marathons, contact Mr Rieger via the Facebook page I Ride With Hame.