diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index aaa1ad6e5ca..8e46364b851 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -1027,6 +1027,7 @@ def select(
         child: Optional[str] = None,
         depflag: dt.DepFlag = dt.ALL,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List[DependencySpec]:
         """Selects a list of edges and returns them.
 
@@ -1046,6 +1047,7 @@ def select(
             child: name of the child package
             depflag: allowed dependency types in flag form
             virtuals: list of virtuals or specific virtual on the edge
+            when: condition on conditional dependency, or Spec() for unconditional dependency only
         """
         if not depflag:
             return []
@@ -1071,6 +1073,9 @@ def select(
             else:
                 selected = (dep for dep in selected if any(v in dep.virtuals for v in virtuals))
 
+        if when is not None:
+            selected = (dep for dep in selected if dep.when == when)
+
         return list(selected)
 
     def clear(self):
@@ -1618,6 +1623,7 @@ def edges_to_dependencies(
         depflag: dt.DepFlag = dt.ALL,
         *,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List[DependencySpec]:
         """Returns a list of edges connecting this node in the DAG to children.
 
@@ -1625,9 +1631,13 @@ def edges_to_dependencies(
             name: filter dependencies by package name
             depflag: allowed dependency types
             virtuals: allowed virtuals
+            when: condition on conditional dependencies (or Spec() for unconditional)
         """
         return [
-            d for d in self._dependencies.select(child=name, depflag=depflag, virtuals=virtuals)
+            d
+            for d in self._dependencies.select(
+                child=name, depflag=depflag, virtuals=virtuals, when=when
+            )
         ]
 
     @property
@@ -1666,6 +1676,7 @@ def dependencies(
         deptype: Union[dt.DepTypes, dt.DepFlag] = dt.ALL,
         *,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List["Spec"]:
         """Returns a list of direct dependencies (nodes in the DAG)
 
@@ -1673,11 +1684,15 @@ def dependencies(
             name: filter dependencies by package name
             deptype: allowed dependency types
             virtuals: allowed virtuals
+            when: condition on conditional dependency or Spec() for unconditional
         """
         if not isinstance(deptype, dt.DepFlag):
             deptype = dt.canonicalize(deptype)
         return [
-            d.spec for d in self.edges_to_dependencies(name, depflag=deptype, virtuals=virtuals)
+            d.spec
+            for d in self.edges_to_dependencies(
+                name, depflag=deptype, virtuals=virtuals, when=when
+            )
         ]
 
     def dependents(