Destroying objects of a Hashtable (only destroy the new objects) Problem

Unity Engine
1

Hi guys,
Im trying to destroy some objects from a Hastable, (basically destroy the objects to certain distance), the problem that i have is that I cant access to the older objects. I can only destroy the new ones.

I want to the destroy and generate objects at a runtime. So I think the problem im having is storing those objects.

//Resume of the code

private Hashtable objects = new Hastable();

void GenerateObject()
{
//Here I create diferent objects to different heights
for(blablabla)
{

                    GameObject target = GameObject.Instantiate(treeOnGrass, positionTreeGrass, Quaternion.identity) as GameObject;
                    string targetName = "TreeOnGrass_" + ((int)(positionTreeGrass.x)).ToString() + "_" + ((int)(positionTreeGrass.z)).ToString();
                    target.name = targetName;
                    TreesAndRocks treeAndRocks = new TreesAndRocks(target, positionTreeGrass);

                    if (!objects.ContainsKey(targetName))
                    {
                        objects.Add(targetName, treeAndRocks);
                    }
                    else {
                        (objects[targetName] as TreesAndRocks).positionObjects = positionTreeGrass;
                    }

}

//other object
for(bla bla bla)

                    GameObject target = GameObject.Instantiate(otherObject, positionTreeGrass, Quaternion.identity) as GameObject;
                    string targetName = "OtherObject" + ((int)(positionTreeGrass.x)).ToString() + "_" + ((int)(positionTreeGrass.z)).ToString();
                    target.name = targetName;
                    TreesAndRocks treeAndRocks = new TreesAndRocks(target, positionTreeGrass);

                    if (!objects.ContainsKey(targetName))
                    {
                        objects.Add(targetName, treeAndRocks);
                    }
                    else {
                        (objects[targetName] as TreesAndRocks).positionObjects = positionTreeGrass;
                    }


}

//Then I have a Destroy function But when I want to access to that Hastable I cant do it to the older objects, for example I cant destroy all
// the objects. Only the ones that are created each time that I generate in that moment

        public void DestroyObjects()
        {
            //Destroy Far Trees and
            Hashtable newObjects = new Hashtable();

            foreach (TreesAndRocks tAr in objects.Values)
            {
          

                if (tAr.positionObjects.x > TerrainChunkGenerator.playerPosition.position.x && TerrainChunkGenerator.activateRemover)
                {
                    UnityEngine.Object.Destroy(tAr.tressAndRocks);
                    Debug.Log(TerrainChunkGenerator.playerPosition.position.x + "_" + TerrainChunkGenerator.playerPosition.position.y + "_" + TerrainChunkGenerator.playerPosition.position.z);
                }
                else
                {
                    newObjects.Add(tAr.tressAndRocks.name, tAr);
                }
            }
            objects = newObjects;
        }

So my queston is … How to ADD to a List, Hastable, o dictionarry, any object. And have the posibility to access later.???.. Thank you

2

To sum up:

I want to add some different objects to a List ( or whatever) and then destroy them based on certain distance to the player.

Any ideas??