diff --git a/.github/workflows/phpunit-tests.yml b/.github/workflows/phpunit-tests.yml
index 63a5442132bdc..46d2f904c157f 100644
--- a/.github/workflows/phpunit-tests.yml
+++ b/.github/workflows/phpunit-tests.yml
@@ -141,8 +141,8 @@ jobs:
   #
   # Creates a PHPUnit test job for each PHP/MariaDB combination.
   #
-  # All LTS versions of MariaDB supported by WordPress with greater than 1% usage according to w.org/stats should be
-  # tested. The exceptions to this rule are the most recent LTS and version 5.5.
+  # Dispatched runs test all LTS versions of MariaDB supported by WordPress with greater than 1% usage according to
+  # w.org/stats. The exceptions to this rule are the most recent LTS and version 5.5.
   #
   # The 5.5 release was intended as a drop-in replacement for MySQL. Because the MySQL 5.5 Docker containers do not
   # work, this ensures some level of MySQL 5.5 testing.
@@ -162,7 +162,8 @@ jobs:
         # Test highest and lowest supported version of each major.
         php: [ '7.4', '8.0', '8.5' ]
         db-type: [ 'mariadb' ]
-        db-version: [ '5.5', '10.3', '10.5', '10.6', '10.11', '11.4', '11.8' ]
+        # Dispatched runs, including the monthly old-branch run, test the full database matrix. Other events retain MariaDB 5.5 compatibility, 10.6, and newer LTS releases.
+        db-version: ${{ github.event_name == 'workflow_dispatch' && fromJSON('["5.5","10.3","10.5","10.6","10.11","11.4","11.8"]') || fromJSON('["5.5","10.6","10.11","11.4","11.8"]') }}
         multisite: [ false, true ]
         memcached: [ false ]