Ashridge is one of the most popular places in the country to see bluebells, with thousands of people coming to see the spectacular carpets of flowers each spring.
The most heavily visited area is Dockey Wood on the Beacon Road. The trust says at weekends during bluebell season traffic queues build up and people park chaotically, damaging verges and wayside plants. The estate now sees around 2,000 cars per day in peak season.
A 2015 survey of visitors to the wood reportedly found people wanted more staff at the woods during busy weekends and were amenable to a small charge being introduced to help meet costs.
In a visitor statement the trust said: "The bluebells at Dockey Wood are under a great amount of foot pressure due to high visitor numbers. The bluebells are being trampled and the ground is being compacted. As a result, the bluebells are declining.
"In past years we've placed signs throughout the wood to try to reduce the damage, but this hasn't worked. This year, we will have rangers on site at the peak times so that we can talk to visitors about our work and how we take care of this special place."
Between 10am and 4pm on 30 April, 1 May, 2 May, 7 and 8 May adults will be charged £3 and children £1 to enter the woods.
The trust says the money will go directly towards caring for Ashridge Estate, which has a yearly maintenance bill of more than £500,000. Entry will remain free for National Trust members, and other bluebell areas around the estate will remain free to visit.
It also hopes the charge will spread visitors more evenly through week - which has worked well at other National Trust properties.
A fence has been built along the roadside at Dockey Wood to safeguard the bluebells and protect the area from erosion and cars, as well as limiting visitors to a single entrance.