diff --git a/backend/src/main/java/core/api/models/timemanager/tasks/TaskEntityInfo.java b/backend/src/main/java/core/api/models/timemanager/tasks/TaskEntityInfo.java
index 28404a9..e322b60 100644
--- a/backend/src/main/java/core/api/models/timemanager/tasks/TaskEntityInfo.java
+++ b/backend/src/main/java/core/api/models/timemanager/tasks/TaskEntityInfo.java
@@ -51,7 +51,7 @@ public class TaskEntityInfo {
         this.hasActiveSchedules = task.hasActiveSchedule();
         this.hasPlannedSchedules = task.hasPlannedSchedules();
         this.hasTaskSerie = task.getTaskSerieItem() != null;
-        this.hasSubtasks = !task.getSubtasks().isEmpty();
+        this.hasSubtasks = task.getSubtasks() != null && !task.getSubtasks().isEmpty();
         this.hasParent = task.getParent() != null;
     }
 
diff --git a/backend/src/main/java/core/repositories/timemanager/ScheduleRepository.java b/backend/src/main/java/core/repositories/timemanager/ScheduleRepository.java
index df72a88..da5e43a 100644
--- a/backend/src/main/java/core/repositories/timemanager/ScheduleRepository.java
+++ b/backend/src/main/java/core/repositories/timemanager/ScheduleRepository.java
@@ -2,10 +2,12 @@ package core.repositories.timemanager;
 
 import core.entities.timemanager.AbstractSchedule;
 import core.entities.timemanager.Taskgroup;
+import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.CrudRepository;
 import org.springframework.stereotype.Repository;
 
+import javax.transaction.Transactional;
 import java.time.LocalDate;
 import java.util.Collection;
 import java.util.List;
@@ -20,4 +22,9 @@ public interface ScheduleRepository extends CrudRepository<AbstractSchedule, Lon
     @Query(value = "SELECT s FROM AbstractSchedule s WHERE s.task.taskgroup.user.username = ?1 AND s.startTime is NOT NULL and s.stopTime is NULL")
     Optional<AbstractSchedule> getActiveScheduleOfUser(String username);
 
+
+    @Modifying
+    @Transactional
+    @Query(value = "DELETE FROM AbstractSchedule a WHERE a.task IN (SELECT t FROM Task t WHERE t.taskgroup = ?1)")
+    void deleteByTaskgroup(Taskgroup taskgroup);
 }
diff --git a/backend/src/main/java/core/services/TaskScheduleService.java b/backend/src/main/java/core/services/TaskScheduleService.java
index 57ed6d2..94c8df0 100644
--- a/backend/src/main/java/core/services/TaskScheduleService.java
+++ b/backend/src/main/java/core/services/TaskScheduleService.java
@@ -7,10 +7,7 @@ import core.api.models.timemanager.taskSchedule.scheduleInfos.AdvancedScheduleIn
 import core.api.models.timemanager.taskSchedule.scheduleInfos.BasicScheduleFieldInfo;
 import core.api.models.timemanager.taskSchedule.ForgottenScheduleInfo;
 import core.api.models.timemanager.taskSchedule.scheduleInfos.ScheduleInfo;
-import core.entities.timemanager.AbstractSchedule;
-import core.entities.timemanager.AdvancedTaskSchedule;
-import core.entities.timemanager.BasicTaskSchedule;
-import core.entities.timemanager.Task;
+import core.entities.timemanager.*;
 import core.repositories.UserRepository;
 import core.repositories.timemanager.AdvancedScheduleRepository;
 import core.repositories.timemanager.ScheduleRepository;
@@ -259,4 +256,8 @@ public class TaskScheduleService {
         schedule.setStopTime(schedule.getStartTime().plusMinutes(manualScheduleStopInfo.getDuration()));
         scheduleRepository.save(schedule);
     }
+
+    public void deleteSchedulesByTaskgroup(Taskgroup taskgroup) {
+        scheduleRepository.deleteByTaskgroup(taskgroup);
+    }
 }
diff --git a/backend/src/main/java/core/services/TaskService.java b/backend/src/main/java/core/services/TaskService.java
index 2074798..168cdda 100644
--- a/backend/src/main/java/core/services/TaskService.java
+++ b/backend/src/main/java/core/services/TaskService.java
@@ -113,6 +113,7 @@ public class TaskService {
 
     public void clearTasks(Taskgroup taskgroup) {
         taskSeriesService.deleteTaskSerieByTaskgroup(taskgroup);
+        taskScheduleService.deleteSchedulesByTaskgroup(taskgroup);
         taskRepository.deleteAllByTaskgroup(taskgroup);
     }
 
diff --git a/backend/src/main/java/core/services/TaskgroupService.java b/backend/src/main/java/core/services/TaskgroupService.java
index ebbc078..b0a2408 100644
--- a/backend/src/main/java/core/services/TaskgroupService.java
+++ b/backend/src/main/java/core/services/TaskgroupService.java
@@ -21,10 +21,12 @@ public class TaskgroupService {
 
     private final TaskgroupRepository taskgroupRepository;
     private final UserRepository userRepository;
+    private final TaskService taskService;
     public TaskgroupService(@Autowired  TaskgroupRepository taskgroupRepository,
-                            @Autowired UserRepository userRepository) {
+                            @Autowired UserRepository userRepository, @Autowired TaskService taskService) {
         this.taskgroupRepository = taskgroupRepository;
         this.userRepository = userRepository;
+        this.taskService = taskService;
     }
 
     public PermissionResult<Taskgroup> getTaskgroupByIDAndUsername(long taskgroupID, String username) {
@@ -97,6 +99,7 @@ public class TaskgroupService {
     }
 
     public void deleteTaskgroup(Taskgroup taskgroup) {
+        taskService.clearTasks(taskgroup);
         taskgroupRepository.delete(taskgroup);
     }