It is strange that my Terraformer doesn't plant trees on landfilled blocks.
I take an experiment. I place a Terraformer on a block half originally was grass and half landfilled from water and afk for about 10hr. All grass part are plant with different trees but the landfilled part still got nothing.

I remember that long ago it does. Is there any changes recently or is it a bug?

Also, my server keeps reporting an error:
3699.985 Script @stdlib/stdlib/area/chunk.lua:38: WARNING: Area for Position not found in package.loaded
3699.985 Script @stdlib/stdlib/area/chunk.lua:38: WARNING: Area for Position not found in package.loaded
3699.986 Script @stdlib/stdlib/area/chunk.lua:38: WARNING: Area for Position not found in package.loaded

as bio industries is the only mod I have that uses stdlib, I suspect it is related

FYI, my server activates these following mods:

CreativeItems_1.5.0.zip
ore-eraser_1.4.3.zip
'Orbital Ion Cannon_1.8.2.zip'
Teleporters_0.2.3.zip
Bio_Industries_0.18.28.zip
Dectorio_0.10.9.zip
vtk-deep-core-mining_2.3.2.zip
longer-belts-redux_1.0.0.zip
'Power Armor MK3_0.2.20.zip'
Robocharger_1.3.0.zip
Shortcuts-ick_1.0.14.zip
stdlib_1.4.5.zip
Factorissimo2_2.4.3.zip
LogisticTrainNetwork_1.14.6.zip
flib_0.5.0.zip
spidertron-extended_0.3.5.zip
stargate_0.1.3.zip
helmod_0.11.18.zip
AsphaltRoads_1.2.0.zip

Update:
I now receive another error:
1261.015 Script @Bio_Industries/control.lua:952: Entered function "solar_mat_built"
1261.015 Script @Bio_Industries/control.lua:955: event: {
define_name = "on_robot_built_tile",
item = {
__self = "userdata"
},
name = 47,
options = {},
robot = {
__self = "userdata"
},
stack = {
__self = "userdata"
},
surface_index = 1,
tick = 56923831,
tile = {
__self = "userdata"
},
tiles = {
{
old_tile = {
__self = "userdata"
},
position = {
x = 1461,
y = -479
}
},
{
old_tile = {
__self = "userdata"
},
position = {
x = 1461,
y = -480
}
},
{
old_tile = {
__self = "userdata"
},
position = {
x = 1460,
y = -480
}
},
{
old_tile = {
__self = "userdata"
},
position = {
x = 1462,
y = -479
}
}
}
}

Thanks for the report! Couldn't fix the problem yet, but I'll continue to find out what's wrong. :-)

By the way, the "error" you've reported in the update is not an error message -- just some debugging output that spams the log file. This has been fixed for 0.18.29, however.

I've finally figured out how the tree planting code really works! Unfortunately it wasn't documented very well, and it wasn't my own code, so I've misunderstood some things. Landfill will have a minimum fertility in the next release, so you will be able to grow trees there -- but due to the low ground fertility, you probably won't grow many trees unless you use fertilizer.

Should be fixed in 0.18.30/1.1.0!