Park volunteers are furious after flowers planted by schoolchildren were pulled up and stolen twice by a thief.
Green-fingered youngsters from Eldon Grove Academy spent two days working with countryside officers and the Friends of Hartlepool Wild Green Spaces group in the northern end of Burn Valley park.
The children’s hard work was spoiled by a man who was seen helping himself to some of the plants just days later.
And he is said to have returned two days later and taken more plants when the volunteers were working in another area of the park.
Anne Brown, of the Friends of Hartlepool’s Wild Green Spaces group, said: “The volunteers are absolutely fuming.
“The children had spent over two days in various parts of the park working hard to improve it for the benefit of the community and their efforts have been praised by the park users.
“It is therefore beyond comprehension that a grown adult feels the need to spoil their efforts.”
The plants were provided from funds obtained from various charities by the volunteers.
They also installed a metal ramp to improve access for disabled visitors.
Mrs Brown added: “Over the past months the volunteers have worked hard to improve the area and have to contend with the mindless vandalism that regularly occurs, with plants being simply uprooted and thrown around.”
The friends group is appealing for people to help them stamp out vandalism by reporting it.
Anyone who witnesses any thefts or vandalism is urged to call police on 101.