diff --git a/releasenotes/notes/timer-optimization-a6babecaf1c7dab8.yaml b/releasenotes/notes/timer-optimization-a6babecaf1c7dab8.yaml
new file mode 100644
index 0000000000..d039664354
--- /dev/null
+++ b/releasenotes/notes/timer-optimization-a6babecaf1c7dab8.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The timer trigger does not enqueue an event for every branch of every
+    project anymore and it now only processes projects actually using the
+    pipeline triggered by a timer.
diff --git a/tests/fixtures/layouts/timer.yaml b/tests/fixtures/layouts/timer.yaml
index e9e9a170db..5aaa4ce9a5 100644
--- a/tests/fixtures/layouts/timer.yaml
+++ b/tests/fixtures/layouts/timer.yaml
@@ -39,6 +39,12 @@
           label: ubuntu-xenial
     run: playbooks/project-bitrot.yaml
 
+- project:
+    name: org/project1
+    check:
+      jobs:
+        - project-test1
+
 - project:
     name: org/project
     check:
diff --git a/tests/unit/test_scheduler.py b/tests/unit/test_scheduler.py
index 15f1ab0e32..158141b8d5 100755
--- a/tests/unit/test_scheduler.py
+++ b/tests/unit/test_scheduler.py
@@ -3375,6 +3375,18 @@ class TestScheduler(ZuulTestCase):
 
         self.assertEqual(len(self.builds), 2)
 
+        merge_count_project1 = 0
+        for job in self.gearman_server.jobs_history:
+            if job.name == b'merger:refstate':
+                args = job.arguments
+                if isinstance(args, bytes):
+                    args = args.decode('utf-8')
+                args = json.loads(args)
+                if args["items"][0]["project"] == "org/project1":
+                    merge_count_project1 += 1
+        self.assertEquals(merge_count_project1, 0,
+                          "project1 shouldn't have any refstate call")
+
         self.executor_server.hold_jobs_in_build = False
         # Stop queuing timer triggered jobs so that the assertions
         # below don't race against more jobs being queued.
diff --git a/zuul/driver/timer/__init__.py b/zuul/driver/timer/__init__.py
index 69cd508746..f3273425d1 100644
--- a/zuul/driver/timer/__init__.py
+++ b/zuul/driver/timer/__init__.py
@@ -79,7 +79,13 @@ class TimerDriver(Driver, TriggerInterface):
                     jobs.append(job)
 
     def _onTrigger(self, tenant, pipeline_name, timespec):
-        for project_name in tenant.layout.project_configs.keys():
+        for project_name, pcs in tenant.layout.project_configs.items():
+            # timer operates on branch heads and doesn't need speculative
+            # layouts to decide if it should be enqueued or not.
+            # So it can be decided on cached data if it needs to run or not.
+            if not [True for pc in pcs if pipeline_name in pc.pipelines]:
+                continue
+
             (trusted, project) = tenant.getProject(project_name)
             for branch in project.source.getProjectBranches(project, tenant):
                 event = TimerTriggerEvent()