diff --git a/doc/source/merger.rst b/doc/source/merger.rst
index e01bc8c7df..82e204b2cc 100644
--- a/doc/source/merger.rst
+++ b/doc/source/merger.rst
@@ -58,3 +58,17 @@ instance, a clone will produce a repository in an unpredictable state
 depending on what the state of Zuul's repository is when the clone
 happens).  They are, however, suitable for automated systems that
 respond to Zuul triggers.
+
+Clearing old references
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The references created under refs/zuul are not garbage collected. Since
+git fetch send them all to Gerrit to sync the repositories, the time
+spent on merge will slightly grow overtime and start being noticeable.
+
+To clean them you can use the ``tools/zuul-clear-refs.py`` script on
+each repositories. It will delete Zuul references that point to commits
+for which the commit date is older than a given amount of days (default
+360)::
+
+  ./tools/zuul-clear-refs.py /path/to/zuul/git/repo
diff --git a/tools/zuul-clear-refs.py b/tools/zuul-clear-refs.py
new file mode 100755
index 0000000000..60ce74422f
--- /dev/null
+++ b/tools/zuul-clear-refs.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python
+# Copyright 2014-2015 Antoine "hashar" Musso
+# Copyright 2014-2015 Wikimedia Foundation Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+# pylint: disable=locally-disabled, invalid-name
+
+"""
+Zuul references cleaner.
+
+Clear up references under /refs/zuul/ by inspecting the age of the commit the
+reference points to.  If the commit date is older than a number of days
+specificed by --until, the reference is deleted from the git repository.
+
+Use --dry-run --verbose to finely inspect the script behavior.
+"""
+
+import argparse
+import git
+import logging
+import time
+import sys
+
+NOW = int(time.time())
+DEFAULT_DAYS = 360
+ZUUL_REF_PREFIX = 'refs/zuul/'
+
+parser = argparse.ArgumentParser(
+    description=__doc__,
+    formatter_class=argparse.RawDescriptionHelpFormatter,
+)
+parser.add_argument('--until', dest='days_ago', default=DEFAULT_DAYS, type=int,
+                    help='references older than this number of day will '
+                         'be deleted. Default: %s' % DEFAULT_DAYS)
+parser.add_argument('-n', '--dry-run', dest='dryrun', action='store_true',
+                    help='do not delete references')
+parser.add_argument('-v', '--verbose', dest='verbose', action='store_true',
+                    help='set log level from info to debug')
+parser.add_argument('gitrepo', help='path to a Zuul git repository')
+args = parser.parse_args()
+
+logging.basicConfig()
+log = logging.getLogger('zuul-clear-refs')
+if args.verbose:
+    log.setLevel(logging.DEBUG)
+else:
+    log.setLevel(logging.INFO)
+
+try:
+    repo = git.Repo(args.gitrepo)
+except git.exc.InvalidGitRepositoryError:
+    log.error("Invalid git repo: %s" % args.gitrepo)
+    sys.exit(1)
+
+for ref in repo.references:
+
+    if not ref.path.startswith(ZUUL_REF_PREFIX):
+        continue
+    if type(ref) is not git.refs.reference.Reference:
+        # Paranoia: ignore heads/tags/remotes ..
+        continue
+
+    try:
+        commit_ts = ref.commit.committed_date
+    except LookupError:
+        # GitPython does not properly handle PGP signed tags
+        log.exception("Error in commit: %s, ref: %s. Type: %s",
+                      ref.commit, ref.path, type(ref))
+        continue
+
+    commit_age = int((NOW - commit_ts) / 86400)  # days
+    log.debug(
+        "%s at %s is %3s days old",
+        ref.commit,
+        ref.path,
+        commit_age,
+    )
+    if commit_age > args.days_ago:
+        if args.dryrun:
+            log.info("Would delete old ref: %s (%s)", ref.path, ref.commit)
+        else:
+            log.info("Deleting old ref: %s (%s)", ref.path, ref.commit)
+            ref.delete(repo, ref.path)