Some 8,000 bluebell bulbs were found dug up after police received a call about suspicious activity in a privately-owned wood.
Officers arrived to find large sacks and mail bags filled with recently uprooted bulbs from the wood in the Fakenham area, Norfolk Police said.
A walker reported seeing people acting suspiciously in the wood on 23 March.
Two men and two women, in their 20s and 30s and all from Lincolnshire, have been interviewed, but no arrests made.
The landowner is in the process of replanting the bulbs and officers are appealing for witnesses.
British bluebells are protected under the Wildlife and Countryside Act along with all other native wild plants and bulbs, said Norfolk Police.
It is an offence to intentionally uproot any wild plant unless authorised to do so, and police are encouraging people to report any suspicious behaviour.
In 2019, almost 13,000 snowdrops worth about £1,500 were stolen from the Walsingham Estate in Norfolk and two men admitted theft and criminal damage.
One was jailed for 10 months and the other ordered to complete 200 hours of unpaid work.