Celebrations for the 125th anniversary of St Luke’s School, Southsea, were expected to last well into the next century.
The school planted a tree and buried a time capsule to tell future generations about Portsmouth in 1989.
Head teacher David Bailey said: ‘The tree will hopefully be here for the next 100 years – who knows what changes will have happened by then.’
The time capsule – containing a school tie, school programmes, letters, and a copy of The News – was buried by head boy Lee Cottrell, 16.
The tree was planted by the school’s youngest pupil Barry Springgay, 12, and Jean Williams, chairwoman of the school’s governors.
It was followed by a service led by former pupil Canon Buckett, the vicar of Newport.