Ten thousand trees will be planted over five hours at Heartwood Forest on Saturday.
The Woodland Trust is inviting volunteers to its final tree planting event of the season at the forest near Sandridge from 10am to 3pm.
The trees are the last of 90,000 that the charity has planted during the course of the winter, all by volunteers.
More than 425,000 have already been planted on site in just five years, with monitoring surveys suggesting the new trees are already having a positive impact on wildlife.
Louise Neicho, Woodland Trust site manager, said: "We’re hoping to have some good spring weather and see plenty of people on site for the last planting event of the winter.
"Every tree we plant helps increase the amount of woodland we have in England, which is much lower than elsewhere in Europe. So not only will volunteers have a fun day out, but they’ll also make a positive contribution to the environment."
Visitors are encouraged to walk, cycle or get the bus but if driving is essential residents can park at Heartwood’s car park, situated off the B651, the main road that runs from Sandridge to Wheathampstead.
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