diff --git a/garden/garden.go b/garden/garden.go
index b399c79..64949b0 100644
--- a/garden/garden.go
+++ b/garden/garden.go
@@ -46,6 +46,11 @@ func Init(root string) (*Garden, error) {
 		return nil, fmt.Errorf("creating store: %w", err)
 	}
 
+	gitignorePath := filepath.Join(absRoot, ".gitignore")
+	if err := os.WriteFile(gitignorePath, []byte("blobs/\n"), 0o644); err != nil {
+		return nil, fmt.Errorf("creating .gitignore: %w", err)
+	}
+
 	clk := clockwork.NewRealClock()
 	m := manifest.NewWithTime(clk.Now().UTC())
 	if err := m.Save(manifestPath); err != nil {
diff --git a/garden/garden_test.go b/garden/garden_test.go
index 1485602..421f580 100644
--- a/garden/garden_test.go
+++ b/garden/garden_test.go
@@ -25,6 +25,14 @@ func TestInitCreatesStructure(t *testing.T) {
 		t.Errorf("blobs/ not found: %v", err)
 	}
 
+	// .gitignore should exist and exclude blobs/
+	gitignore, err := os.ReadFile(filepath.Join(repoDir, ".gitignore"))
+	if err != nil {
+		t.Errorf(".gitignore not found: %v", err)
+	} else if string(gitignore) != "blobs/\n" {
+		t.Errorf(".gitignore content = %q, want %q", gitignore, "blobs/\n")
+	}
+
 	if g.manifest.Version != 1 {
 		t.Errorf("expected version 1, got %d", g.manifest.Version)
 	}