How to use static List with interface in .net?

I want to use a static List with an interface in .net

I wonder where in the code I should declare my List : in the interface class, in the derived classes, or somewhere else ?

For the moment I have it declared in the derived class (BacFlo).

My problem is : I can't populate the List correctly, it seems like the List is empty when it shouldn't.

Here is an extract of my code :

Interface :

 public interface Serre
    {
        void Plant(Plante p);
        void Remove(string s);
        void Water(string s);
        void Clone(string s);
        void Inventory();
    }

Derived Class #1 :

public class BacFlo : Serre
    {
        static List<Plante> Garden = new List<Plante>();

        }

My main class :

    Serre bc = new BacCro();
    Serre bf = new BacFlo();

for (int i = 0; i < 10; i++)
        {
            Plante p = new Plante("Plante commune", "Vivace", "Une plante", 120);
            bf.Plant(p);
            bc.Plant(p);
        }

        for (int i = 0; i < 10; i++)
        {
            Plante p = new Plante("Plante rare", "à bulbe", "Une plante", 10);
            bf.Planter(p);
            bc.Planter(p);
        }

        bf.Inventory();
        bc.Inventory();

}

   void Serre.Inventory()
        {
            Console.WriteLine("");
            Console.WriteLine("Inventaire du bac de floraison :");
            foreach (Plante p in Jardin)
            {
                Console.WriteLine("Plante de nom " + p.Name + ", de type " + p.Type + ", de description " + p.Description + ", de taille " + p.Taille + ", Arrosée : " + (p.IsWet == true ? "Oui" : "Non"));
        }

What I want to achieve is correctly populate the List with my for loop and have displayed the inventory with the appropriate method.

I'm not sure about the instanciation of a static List...

What it seems you have is some sort of Garden concept, which is basically a collection of Plants. And Serre seems to interface how to interact with Gardens.

I am not sure about how the BacXYZ family of classes is related to this, but you seem to want a group (if not all) instances of BacXYZ classes to interact with the same Garden. (Maybe think about that you later on may want different groups of BacXYZ to act upon different Gardens?)

So, the natural thing for me would be to either

• include the Garden as an argument to Serre's methods or
• inject the Garden to each BacXYZ instance upon creation.

As I suspect you will be leaning to the latter one:

You could do this:

public class BacFlo : Serre
{
    private readonly ICollection<Plant> _garden;
    
    public BacFlo( ICollection<Plant> garden )
    {
        ArgumentNullException.ThrowIfNull(garden);
        _garden = garden;
    }

    // Serre-Implementations here
}

Now, in the caller:

public void Main()
{
    var garden = new List<Plant>(); // Could also be a class field or whatever

    var bac1 = new BacFlo(garden);
    var bac2 = new BacFlo(garden);
    var bac3 = new BacFlo(garden);
}

^^ All of these would operate on the same garden list. No static needed.

This usage of keyword "static" seems unnecessary to me. In most cases root variable members in classes are declared Public, Private or Protected.

Here is related question on Stack Overflow

Being you I would used Private instead of Static. Behaviour of Static variables may have strange effects on programming logic. Using keyword Static mostly have some sense when in the function / procedure scope, but its usage is marginal. I can't imagine reason for declaring instance of List in class Static, you may need to do some research on Static, Private, Public and Protected, before you decide e.g. for using Static