IEnumerator WaitForSeconds not working in Unity

Question

I'm currently working on an ecosystem simulation project. The first mechanic I'm trying to work on is trees/plants spreading. I have a script that I attach to my tree that processes as follows:

(1) Check if tree is mature, if it is generateSpawner(); (2),treeMature Grow (Not implemented yet, I just have bool treeMature = true)

(3) GenerateSpawner works by checking random coordinates in a circle around the tree for any pre-existing plants. If there is not a plant, the script generates a spawner, then waits for a 120 seconds before checking again.

(4) If there is a plant the program is supposed to wait 30 seconds then check another spot.

The issue lies in the wait portion. Both in the spawning portion and in the non-spawning portion. The script rapidly creates spawners, or if I don't allow the script to create spawners the script rapidly generates checks.

Here's the code, why isn't my IEnumerator working?

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlantAI : MonoBehaviour
{
    public GameObject plantSpawn, thisPlant;
    public LayerMask WhatIsPlant;
    public Vector3 clearingCheck;

    bool treeMature = true, plantAdjacent, isClearing;


    public float spawnRange;
    

    void Start()
    {
        if (treeMature) GenerateSpawner();
        if (!treeMature) Grow();
    }

    void Update()
    {
        if (treeMature) GenerateSpawner();
        if (!treeMature) Grow();
    }

    private void GenerateSpawner()
    {
        StartCoroutine(LookForClearing());            
    }

    IEnumerator LookForClearing()
    {
        float deltaZ = UnityEngine.Random.Range(-spawnRange, spawnRange);
        float deltaX = UnityEngine.Random.Range(-spawnRange, spawnRange);
        clearingCheck = new Vector3(thisPlant.transform.position.x + deltaX, thisPlant.transform.position.y, thisPlant.transform.position.z + deltaZ);
        plantAdjacent = Physics.CheckSphere(clearingCheck, spawnRange, WhatIsPlant);

        if (!plantAdjacent) isClearing = true;

        if (isClearing)
        {
            GameObject spawn = Instantiate(plantSpawn, thisPlant.transform.position, Quaternion.AngleAxis(UnityEngine.Random.Range(0, 359), Vector3.up));
            isClearing = false;
            yield return new WaitForSeconds(120);
        }

        if (!isClearing)
        {
            yield return new WaitForSeconds(30);
        }
        
    }

    private void Grow()
    {
        throw new NotImplementedException();
    }
}

Answer 1

It rapidly generate checks because GenerateSpawner() it's in the Update() and thus will trigger the coroutine. If you need to wait and start over, you can use a delegate to be called when completed.

Alternatively, you may want to not call the spawner, in the Update() and just in the Start() .

Try modifying the spawner like this so it's waiting for the WaitForSeconds() to continue code execution.

IEnumerator LookForClearing()
{
    float deltaZ = UnityEngine.Random.Range(-spawnRange, spawnRange);
    float deltaX = UnityEngine.Random.Range(-spawnRange, spawnRange);
    clearingCheck = new Vector3(thisPlant.transform.position.x + deltaX, thisPlant.transform.position.y, thisPlant.transform.position.z + deltaZ);
    plantAdjacent = Physics.CheckSphere(clearingCheck, spawnRange, WhatIsPlant);

    if (!plantAdjacent) isClearing = true;

    if (isClearing)
    {
        yield return new WaitForSeconds(120.0f);
        GameObject spawn = Instantiate(plantSpawn, thisPlant.transform.position, Quaternion.AngleAxis(UnityEngine.Random.Range(0, 359), Vector3.up));
        isClearing = false;
        Debug.Log("Spawn a plant!");
    }
    if (!isClearing)
    {
        yield return new WaitForSeconds(30.0f);
        Debug.Log("Wait another 30s");
    }

    StartCoroutine(LookForClearing());
}