How to start a coroutine from another script?

So i've looked around on here for a couple of days, and I can't seem to get anything to work. I have a class that controls an enemy spawn. The enemies are just spheres. The C# script uses a couroutine to creat the spheres. I want the coroutine to be called when the player collides with a specific box collider with rigidbody. My Spawn script that is attached to an empty game object:

 using UnityEngine;
 using System;
 using System.Collections;
 
 public class Spawn : MonoBehaviour {
     public GameObject[] sphere;
     public static event Action created;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
 
     }
 
     IEnumerator createSphere(float seconds) {
         yield return new WaitForSeconds(seconds);
         GameObject copy = Instantiate(sphere[(int)UnityEngine.Random.Range(0.0f,4.0f)], transform.position, Quaternion.identity) as GameObject;
         copy.rigidbody.velocity = UnityEngine.Random.onUnitSphere * UnityEngine.Random.Range (5, 10);
         if(created != null) {
             created();
         }
         //direction = Random.onUnitSphere;
         //StartCoroutine (createSphere(seconds));
     }
 
     public void startSpawn() {
         StartCoroutine(createSphere(5f));
     }
     
 }
 

My SpawnTrigger script that is attached to the box collider with rigidbody:

 using UnityEngine;
 using System.Collections;
 
 public class SpawnTrigger : MonoBehaviour {
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     void OnCollisionEnter(Collision collision) {
         if (collision.gameObject.tag == "Player") {
             Spawn.startSpawn();
         }
     }
 }

I'm getting this error: An object reference is required for the non-static field, method, or property Spawn.startSpawn(); which is near the bottom of the second script. Any help? Thanks! Corey