diff --git a/generic3g/specs/FieldSpec.F90 b/generic3g/specs/FieldSpec.F90
index 3bf137f27686..168e1d532df9 100644
--- a/generic3g/specs/FieldSpec.F90
+++ b/generic3g/specs/FieldSpec.F90
@@ -477,18 +477,22 @@ logical function can_connect_to(this, src_spec, rc)
       class(StateItemSpec), intent(in) :: src_spec
       integer, optional, intent(out) :: rc
 
-      logical :: can_convert_units_
+      logical :: can_convert_units
+      logical :: can_connect_vertical_grid
       integer :: status
 
       select type(src_spec)
       class is (FieldSpec)
-         can_convert_units_ = can_connect_units(this%units, src_spec%units, _RC)
+         can_convert_units = can_connect_units(this%units, src_spec%units, _RC)
+         can_connect_vertical_grid = this%vertical_grid%can_connect_to(src_spec%vertical_grid, _RC)
+
          can_connect_to = all ([ &
               can_match(this%geom,src_spec%geom), &
+              can_connect_vertical_grid, &
               match(this%vertical_dim_spec,src_spec%vertical_dim_spec), &
               match(this%ungridded_dims,src_spec%ungridded_dims), &
               includes(this%attributes, src_spec%attributes), &
-              can_convert_units_ &
+              can_convert_units &
               ])
       class default
          can_connect_to = .false.
@@ -636,16 +640,16 @@ subroutine make_extension_safely(this, dst_spec, new_spec, action, rc)
          _RETURN(_SUCCESS)
       end if
       
-   _ASSERT(allocated(this%vertical_grid), 'Source spec must specify a valid vertical grid.')
-   if (.not. same_vertical_grid(this%vertical_grid, dst_spec%vertical_grid)) then
-      _HERE
-      call this%vertical_grid%get_coordinate_field(v_in_coord, v_in_coupler, &
-           'ignore', this%geom, this%typekind, this%units, _RC)
-      call this%vertical_grid%get_coordinate_field(v_out_coord, v_out_coupler, &
-           'ignore', dst_spec%geom, dst_spec%typekind, dst_spec%units, _RC)
-      action = VerticalRegridAction(v_in_coord, v_out_coupler, v_out_coord, v_out_coupler, VERTICAL_REGRID_LINEAR)
-      _RETURN(_SUCCESS)
-   end if
+      _ASSERT(allocated(this%vertical_grid), 'Source spec must specify a valid vertical grid.')
+      if (.not. same_vertical_grid(this%vertical_grid, dst_spec%vertical_grid)) then
+         _HERE
+         call this%vertical_grid%get_coordinate_field(v_in_coord, v_in_coupler, &
+              'ignore', this%geom, this%typekind, this%units, _RC)
+         call this%vertical_grid%get_coordinate_field(v_out_coord, v_out_coupler, &
+              'ignore', dst_spec%geom, dst_spec%typekind, dst_spec%units, _RC)
+         action = VerticalRegridAction(v_in_coord, v_out_coupler, v_out_coord, v_out_coupler, VERTICAL_REGRID_LINEAR)
+         _RETURN(_SUCCESS)
+      end if
       
 !#   if (.not. same_freq_spec(this%freq_spec, dst_spec%freq_spec)) then
 !#      action = VerticalRegridAction(this%freq_spec, dst_spec%freq_spec
@@ -720,6 +724,7 @@ logical function can_match_geom(a, b) result(can_match)
 
    end function can_match_geom
 
+
    logical function match_geom(a, b) result(match)
       type(ESMF_Geom), allocatable, intent(in) :: a, b
 
diff --git a/generic3g/vertical/BasicVerticalGrid.F90 b/generic3g/vertical/BasicVerticalGrid.F90
index b0e6d9eb91fd..b8eb6d5410f4 100644
--- a/generic3g/vertical/BasicVerticalGrid.F90
+++ b/generic3g/vertical/BasicVerticalGrid.F90
@@ -17,6 +17,7 @@ module mapl3g_BasicVerticalGrid
    contains
       procedure :: get_num_levels
       procedure :: get_coordinate_field
+      procedure :: can_connect_to
    end type BasicVerticalGrid
 
    interface operator(==)
@@ -31,6 +32,15 @@ module mapl3g_BasicVerticalGrid
       module procedure new_BasicVerticalGrid
    end interface BasicVerticalGrid
 
+   interface
+      module function can_connect_to(this, src, rc)
+         logical :: can_connect_to
+         class(BasicVerticalGrid), intent(in) :: this
+         class(VerticalGrid), intent(in) :: src
+         integer, optional, intent(out) :: rc
+      end function
+   end interface
+
 contains
 
    function new_BasicVerticalGrid(num_levels) result(vertical_grid)
@@ -69,4 +79,5 @@ elemental logical function not_equal_to(a, b)
       not_equal_to = .not. (a == b)
    end function not_equal_to
 
+
 end module mapl3g_BasicVerticalGrid
diff --git a/generic3g/vertical/BasicVerticalGrid/can_connect_to.F90 b/generic3g/vertical/BasicVerticalGrid/can_connect_to.F90
new file mode 100644
index 000000000000..3cc14928c4fb
--- /dev/null
+++ b/generic3g/vertical/BasicVerticalGrid/can_connect_to.F90
@@ -0,0 +1,27 @@
+#include "MAPL_ErrLog.h"
+submodule (mapl3g_BasicVerticalGrid) can_connect_to_smod
+   use mapl3g_MirrorVerticalGrid
+   use mapl3g_ModelVerticalGrid
+
+contains
+
+   logical module function can_connect_to(this, src, rc)
+      class(BasicVerticalGrid), intent(in) :: this
+      class(VerticalGrid), intent(in) :: src
+      integer, optional, intent(out) :: rc
+
+      select type(src)
+      type is (BasicVerticalGrid)
+         can_connect_to = (this%get_num_levels() == src%get_num_levels())
+      type is (MirrorVerticalGrid)
+         can_connect_to = .true.
+      type is (ModelVerticalGrid)
+         can_connect_to = (this%get_num_levels() == src%get_num_levels())
+      class default
+         _FAIL('BasicVerticalGrid can only connect to src BasicVerticalGrid, MirrorVerticalGrid, or ModelVerticalGrid instances.')
+      end select
+
+      _RETURN(_SUCCESS)
+   end function can_connect_to
+
+end submodule
diff --git a/generic3g/vertical/CMakeLists.txt b/generic3g/vertical/CMakeLists.txt
index ad3eebcd41a2..1d9d4fa43656 100644
--- a/generic3g/vertical/CMakeLists.txt
+++ b/generic3g/vertical/CMakeLists.txt
@@ -5,4 +5,17 @@ target_sources(MAPL.generic3g PRIVATE
   MirrorVerticalGrid.F90
   FixedLevelsVerticalGrid.F90
   ModelVerticalGrid.F90
-  )
+)
+
+esma_add_fortran_submodules(
+  TARGET MAPL.generic3g
+  SUBDIRECTORY BasicVerticalGrid
+  SOURCES can_connect_to.F90
+)
+
+esma_add_fortran_submodules(
+  TARGET MAPL.generic3g
+  SUBDIRECTORY ModelVerticalGrid
+  SOURCES can_connect_to.F90
+)
+
diff --git a/generic3g/vertical/FixedLevelsVerticalGrid.F90 b/generic3g/vertical/FixedLevelsVerticalGrid.F90
index 4ac4088198df..08bd7b24fd47 100644
--- a/generic3g/vertical/FixedLevelsVerticalGrid.F90
+++ b/generic3g/vertical/FixedLevelsVerticalGrid.F90
@@ -22,6 +22,7 @@ module mapl3g_FixedLevelsVerticalGrid
    contains
       procedure :: get_num_levels
       procedure :: get_coordinate_field
+      procedure :: can_connect_to
    end type FixedLevelsVerticalGrid
 
    interface FixedLevelsVerticalGrid
@@ -58,5 +59,14 @@ subroutine get_coordinate_field(this, field, coupler, standard_name, geom, typek
        _FAIL('not implemented')
     end subroutine get_coordinate_field
 
+    logical function can_connect_to(this, src, rc)
+       class(FixedLevelsVerticalGrid), intent(in) :: this
+       class(VerticalGrid), intent(in) :: src
+       integer, optional, intent(out) :: rc
+
+       _FAIL('not implemented')
+
+    end function can_connect_to
+
 end module mapl3g_FixedLevelsVerticalGrid
    
diff --git a/generic3g/vertical/MirrorVerticalGrid.F90 b/generic3g/vertical/MirrorVerticalGrid.F90
index 0986d7a856de..15feb6166a10 100644
--- a/generic3g/vertical/MirrorVerticalGrid.F90
+++ b/generic3g/vertical/MirrorVerticalGrid.F90
@@ -21,6 +21,7 @@ module mapl3g_MirrorVerticalGrid
    contains
       procedure :: get_num_levels
       procedure :: get_coordinate_field
+      procedure :: can_connect_to
    end type MirrorVerticalGrid
 
    interface MirrorVerticalGrid
@@ -52,4 +53,13 @@ subroutine get_coordinate_field(this, field, coupler, standard_name, geom, typek
       _FAIL('MirrorVerticalGrid should have been replaced before this procedure was called.')
    end subroutine get_coordinate_field
 
+   logical function can_connect_to(this, src, rc)
+      class(MirrorVerticalGrid), intent(in) :: this
+      class(VerticalGrid), intent(in) :: src
+      integer, optional, intent(out) :: rc
+
+      can_connect_to = .false.
+      _RETURN(_SUCCESS)
+   end function
+
 end module mapl3g_MirrorVerticalGrid
diff --git a/generic3g/vertical/ModelVerticalGrid.F90 b/generic3g/vertical/ModelVerticalGrid.F90
index d65f9fc9e39b..080fdffc08a5 100644
--- a/generic3g/vertical/ModelVerticalGrid.F90
+++ b/generic3g/vertical/ModelVerticalGrid.F90
@@ -35,6 +35,7 @@ module mapl3g_ModelVerticalGrid
    contains
       procedure :: get_num_levels
       procedure :: get_coordinate_field
+      procedure :: can_connect_to
 
       ! subclass-specific methods
       procedure :: add_variant
@@ -47,6 +48,14 @@ module mapl3g_ModelVerticalGrid
       procedure new_ModelVerticalGrid_basic
    end interface ModelVerticalGrid
 
+   interface
+      module function can_connect_to(this, src, rc)
+         logical :: can_connect_to
+         class(ModelVerticalGrid), intent(in) :: this
+         class(VerticalGrid), intent(in) :: src
+         integer, optional, intent(out) :: rc
+      end function
+   end interface
 
    ! TODO:
    ! - Ensure that there really is a vertical dimension
@@ -180,4 +189,6 @@ subroutine get_coordinate_field(this, field, coupler, standard_name, geom, typek
 
     end subroutine get_coordinate_field
 
+
+
 end module mapl3g_ModelVerticalGrid
diff --git a/generic3g/vertical/ModelVerticalGrid/can_connect_to.F90 b/generic3g/vertical/ModelVerticalGrid/can_connect_to.F90
new file mode 100644
index 000000000000..595c2f0f7397
--- /dev/null
+++ b/generic3g/vertical/ModelVerticalGrid/can_connect_to.F90
@@ -0,0 +1,36 @@
+#include "MAPL_ErrLog.h"
+submodule (mapl3g_ModelVerticalGrid) can_connect_to_smod
+   use mapl3g_BasicVerticalGrid
+   use mapl3g_MirrorVerticalGrid
+
+contains
+
+    logical module function can_connect_to(this, src, rc)
+       use mapl3g_MirrorVerticalGrid, only: MirrorVerticalGrid
+       use mapl3g_BasicVerticalGrid, only: BasicVerticalGrid
+       class(ModelVerticalGrid), intent(in) :: this
+       class(VerticalGrid), intent(in) :: src
+       integer, optional, intent(out) :: rc
+       
+       integer :: status
+       
+       if (this%same_id(src)) then
+          can_connect_to = .true.
+          _RETURN(_SUCCESS)
+       end if
+       
+       select type (src)
+       type is (MirrorVerticalGrid)
+          can_connect_to = .true.
+          _RETURN(_SUCCESS)
+       type is (BasicVerticalGrid)
+          can_connect_to = (this%get_num_levels() == src%get_num_levels())
+          _RETURN(_SUCCESS)
+       class default
+          _FAIL('unsupported subclass of VerticalGrid')
+       end select
+
+        _RETURN(_SUCCESS)
+    end function can_connect_to
+
+end submodule
diff --git a/generic3g/vertical/VerticalGrid.F90 b/generic3g/vertical/VerticalGrid.F90
index 1c8e1fd2cfe3..2efa7ee4554f 100644
--- a/generic3g/vertical/VerticalGrid.F90
+++ b/generic3g/vertical/VerticalGrid.F90
@@ -13,6 +13,7 @@ module mapl3g_VerticalGrid
    contains
       procedure(I_get_num_levels), deferred :: get_num_levels
       procedure(I_get_coordinate_field), deferred :: get_coordinate_field
+      procedure(I_can_connect_to), deferred :: can_connect_to
 
 
       procedure :: set_id
@@ -43,6 +44,13 @@ subroutine I_get_coordinate_field(this, field, coupler, standard_name, geom, typ
        character(*), intent(in) :: units
        integer, optional, intent(out) :: rc
     end subroutine I_get_coordinate_field
+
+    logical function I_can_connect_to(this, src, rc) result(can_connect_to)
+       import VerticalGrid
+       class(VerticalGrid), intent(in) :: this
+       class(VerticalGrid), intent(in) :: src
+       integer, optional, intent(out) :: rc
+    end function I_can_connect_to
       
    end interface