I would not use landuse=farmland and rely on the produce tag. This in general violates the principle of least surprise. I think that landuse=plant_nursery is the most widely used tag for this purpose. See the wiki [wiki][1]. Note that christmas trees may be one of several species of conifer. [1]: https://wiki.openstreetmap.org/wiki/Tag%3Alanduse%3Dplant_nursery#Christmas_tree_plantation.

I would not use landuse=farmland and rely on the produce tag. This in general violates the principle of least surprise. I think that landuse=plant_nursery is the most widely used tag for this purpose. See the wiki https://wiki.openstreetmap.org/wiki/Tag%3Alanduse%3Dplant_nursery#Christmas_tree_plantation.