Westonbirt Arboretum has reported an "incredibly high" 97 per cent tree survival rate.
The Silk Wood Community Planting Project team, along with volunteers, conducted a 'beat-up survey' in the last week of August.
Out of 2,150 saplings, 2,083 survived the summer, significantly higher than the industry standard of 85 per cent.
Groups including primary schools, refugee support charities, environmental youth groups, special educational needs schools and colleges, and support groups for adults with learning difficulties have cared for the trees.
Ruth Powell, from Stroud Valley Project, whose visiting group has some adult volunteers with learning difficulties, said: "Everyone loves to be outside doing practical work, and we’ve had feedback of how relaxed and comfortable they all feel being in the trees at Westonbirt."
In addition to caring for the saplings, the groups also took part in wellbeing, art, and activity days.
These days included learning how to measure a tree to determine its carbon storage potential and how to identify different species.
David, a volunteer with the Stroud Valley Project, said: "I’m here today to identify trees and take all the weeds away, and looking at all this is amazing.
"It’s going to look really good in the future because that’s one of the most important things, for other people to come and see what we’ve done."
Three years ago, more than 6.5 hectares of native ash trees in Silk Wood were felled due to Chalara ash dieback, a fungal disease.
Since then, 3,300 native trees have been planted by more than 600 volunteers, with many returning to help look after their trees throughout the summer.
This included mulching - spreading wood chip around the saplings to suppress weeds and retain moisture - and pulling encroaching bramble and thistles.
Across only 18 tree-care days, more than 2,000 trees were cared for, with 35 tonnes of mulch laid by 476 volunteers.
Silk Wood Community Planting Project engagement officer, Meg Walder-Hills, said: "It’s been fantastic having the groups that planted trees in the winter back to look after them, they’ve really enjoyed seeing how well their trees are doing."
The planting project's manager, Oscar Adams, added: "This is an amazing tree survival rate which is incredible for the project and will hopefully be the same for the rest of the planting we do in the coming years.
"All the volunteers should be incredibly proud, and we look forward to welcoming more groups this coming planting season."
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