Trying to set up a planting and harvesting system, but it only works in one trigger area?

What I want to happen is when the player presses alt, some time passes and an object is instantiated there. I also want it so that the player can't instantiate another object there until they've collecting the one they've planted there already. This is working when I only have one planting area, but once I have more than one planting area it no longer works- for some reason I'm only able to keep planting and collecting in just one of the trigger areas instead of all of them. What am I doing wrong?

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class PowerFarmCoroutine : MonoBehaviour {
6.  
7.     public bool instantiated;
8.     public bool inside;
9.     public bool collected;
10.     private IEnumerator coroutine;
11.     public GameObject powerorb;
12.     public Material[] material;
13.     Renderer rend;
14.  
15.     void OnTriggerStay2D(Collider2D Collider2D)
16.     {
17.         if (Collider2D.gameObject.tag == "Player")
18.         {
19.             if (instantiated == false)
20.             {
21.                 inside = true;
22.             }
23.  
24.             if (collected == true)
25.             {
26.                 instantiated = false;
27.                 collected = false;
28.                 rend.sharedMaterial = material[0];
29.             }
30.         }
31.     }
32.  
33.     void OnTriggerExit2D(Collider2D Collider2D)
34.     {
35.         inside = false;
36.     }
37.  
38.  
39.         // Use this for initialization
40.     void Start () {
41.  
42.         rend = GetComponent<Renderer>();
43.         rend.enabled = true;
44.     }
45.    
46.     // Update is called once per frame
47.     void Update () {  
48.  
49.         if (inside && Input.GetKeyDown(KeyCode.LeftAlt))
50.         {
51.             StartCoroutine("spawning");
52.         }
53.  
54.  
55.         if (instantiated == true)
56.         {
57.             StopCoroutine("spawning");        
58.         }
59.     }
60.  
61.     IEnumerator spawning()
62.     {
63.         rend.sharedMaterial = material[1];
64.  
65.         yield return new WaitForSeconds(8);
66.         Instantiate(powerorb, transform.position, transform.rotation);
67.         instantiated = true;
68.         inside = false;
69.        
70.         yield return null;
71.        
72.     }
73. }
74.  

I reference if the object has been collected in another script with this:

Code (CSharp):

1.  if (collecting)
2.             {
3.                 GameObject.FindWithTag("PowerFarm").GetComponent<PowerFarmCoroutine>().collected =
4.             true;
5.                 Destroy(gameObject);
6.             }