Trees worth more than £2,000 have been stolen from gardens in Radlett and Aldenham in the past month.
In the first theft, three trees were stolen the front garden of a house in Roundbush Lane, Aldenham between 11.30pm on Saturday, April 12, and 8.30am on Sunday, April 20.
The trees, which were described as "decorative", were worth around £1,000. Two trees were pruned to have a spiral effect and the other was a cone shape. All were around 4ft tall.
The second theft took place in Goodyers Avenue in Radlett between 4pm on Friday, April 25 and 1pm on Saturday, April 26.
Two trees chained to the ground and worth £1,500 were taken. They were also pruned to a spiral shape were around seven foot tall.
The police have not linked the thefts. Members of community information service OWL received a message urging anyone with information to come forward, and reminding the public to secure their trees so they are not targeted.
Anyone with any information, or anyone that has been offered the trees is asked to call Hertfordshire Police on their non emergency line 101 quoting the crime reference number J1/14/1065 for the first offence and J1/14/1127 for the second.