How to display data in listview using StreamBuilder from Realtime DB in flutter

As @Uni mentioned you can provide the initialData to your StreamBuilder but I would also recommend to always write your code to be prepared for every case the state can have like so:

final dbRef = FirebaseDatabase.instance
      .reference()
      .child("IDh04V383uYGQQfWlVWp2XsdR0J3")
      .child("PlantData");

  List lists = List();


@override
  Widget build(BuildContext context) {
    return Scaffold(
      
      body: Container(
        child: StreamBuilder(
          stream: dbRef.onValue,
          builder: (context, AsyncSnapshot<Event> snapshot) {
            if (snapshot.hasData && !event.hasError &&
            event.data.snapshot.value != null) {
              print("Error on the way");
              lists.clear();
              DataSnapshot dataValues = snapshot.data.snapshot;
              Map<dynamic, dynamic> values = dataValues.value;
              values.forEach((key, values) {
                lists.add(values);
              });
              return new ListView.builder(
                shrinkWrap: true,
                itemCount: lists.length,
                itemBuilder: (BuildContext context, int index) {
                  return Card(
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: <Widget>[
                        Text("Name: " + lists[index]["smartID"]),
                        Text("Image: " + lists[index]["plantname"]),
                      ],
                    ),
                  );
                },
              );
            }
            return Container(child: Text("Add Plants"));
          },
        ),
      ),
      
    );

You should also handle the state when your data is loading and also when you have an error. That way you should not get any surprises.