diff --git a/plants/migrations/0002_alter_pruninglog_plant_alter_species_max_height_cm.py b/plants/migrations/0002_alter_pruninglog_plant_alter_species_max_height_cm.py
new file mode 100644
index 0000000..9ef602b
--- /dev/null
+++ b/plants/migrations/0002_alter_pruninglog_plant_alter_species_max_height_cm.py
@@ -0,0 +1,24 @@
+# Generated by Django 5.1.15 on 2026-05-27 17:58
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('plants', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='pruninglog',
+            name='plant',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='pruning_logs', to='plants.plant'),
+        ),
+        migrations.AlterField(
+            model_name='species',
+            name='max_height_cm',
+            field=models.PositiveIntegerField(blank=True, null=True),
+        ),
+    ]
diff --git a/plants/models.py b/plants/models.py
index 1ee059d..eda0716 100644
--- a/plants/models.py
+++ b/plants/models.py
@@ -8,7 +8,7 @@ class Species(models.Model):
     watering = models.CharField(max_length=100, blank=True)
     sunlight = models.CharField(max_length=200, blank=True)
     shadow_tolerance = models.CharField(max_length=100, blank=True)
-    max_height_cm = models.IntegerField(null=True, blank=True)
+    max_height_cm = models.PositiveIntegerField(null=True, blank=True)
     growth_rate = models.CharField(max_length=100, blank=True)
     growth_season = models.CharField(max_length=100, blank=True)
     pruning_months = models.JSONField(default=list)
@@ -45,7 +45,7 @@ class Plant(models.Model):
 
 class PruningLog(models.Model):
     plant = models.ForeignKey(
-        Plant, on_delete=models.CASCADE, related_name='pruninglogs',
+        Plant, on_delete=models.CASCADE, related_name='pruning_logs',
     )
     pruned_on = models.DateField()
     notes = models.TextField(blank=True)
diff --git a/plants/tests/test_models.py b/plants/tests/test_models.py
index 5c14eee..3b3f298 100644
--- a/plants/tests/test_models.py
+++ b/plants/tests/test_models.py
@@ -33,3 +33,18 @@ def test_pruning_log_str():
 def test_plant_pruning_months_default():
     p = Plant.objects.create(name='Fern', location='Office')
     assert p.pruning_months == []
+
+
+@pytest.mark.django_db
+def test_species_pruning_months_default():
+    s = Species.objects.create(common_name='Oak')
+    assert s.pruning_months == []
+
+
+@pytest.mark.django_db
+def test_delete_species_nulls_plant_species():
+    s = Species.objects.create(common_name='Rose')
+    p = Plant.objects.create(name='Garden rose', location='Garden', species=s)
+    s.delete()
+    p.refresh_from_db()
+    assert p.species is None