The National Memorial Arboretum is facing a large bill after more than 1,000 of its trees were damaged during the summer floods.
The Queen is due to visit the site in October
The trees in Alrewas, Staffordshire, were planted to honour those who have died in wars around the world.
Grounds Maintenance Manager Barry Jones said it would cost thousands of pounds and more than a year to put matters right.
The Queen is due to open a new memorial at the arboretum site on 12 October.
The Armed Forces Memorial is a tribute to those who have died on duty since World War II or who have suffered as a result of conflict.
But work to build the memorial has been delayed because water got into cabs and engines of machines which had to be replaced.
The Arboretum consists of 150 acres of wooded parkland within the National Forest.