smooth speed decrease

Good Evening,

I created a scrolling infinite background for my game and it offsets the material on a quad using this code: using UnityEngine; using System.Collections;

public class Scrolling : MonoBehaviour { public float speed = 0.0f;

 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () 
 {
     GetComponent<Renderer>().material.mainTextureOffset =  new Vector2 (Time.time * speed, 0);


 }

}

my character is being shot out of cannon and i want speed to slow down over time. So I added this code to my game for when the game starts.

using UnityEngine; using System.Collections; using DG.Tweening;

public class GameStart : MonoBehaviour {

 public float speed = 0.0f;
 public float timer = 0.0f;
 public float speed_timer = 0.0f;
 public float reset_speed_timer = 0.0f;
 public GameObject Background;
 public GameObject Water;
 public GameObject BackgroundTrees;
 public GameObject ForegroundTrees;
 public GameObject ForegroundClouds;
 public GameObject MidGroundClouds;
 public GameObject Knife;


 private Scrolling BGScrollScript;
 private Scrolling waterScrollScript;
 private Scrolling BGTreeScrollScript;
 private Scrolling FGTreeScrollScript;
 private Scrolling FGCloudScrollScript;
 private Scrolling MGCouldScrollSCript;
 private Knife_Move knifeTween;



 public GameObject parentGameobject;


 // Use this for initialization
 void Start ()
 {
     BGScrollScript = Background.GetComponent<Scrolling> ();
     waterScrollScript = Water.GetComponent<Scrolling> ();
     BGTreeScrollScript = BackgroundTrees.GetComponent<Scrolling> ();
     FGTreeScrollScript = ForegroundTrees.GetComponent<Scrolling> ();
     FGCloudScrollScript = ForegroundClouds.GetComponent<Scrolling> ();
     MGCouldScrollSCript = MidGroundClouds.GetComponent<Scrolling> ();
     knifeTween = Knife.GetComponent<Knife_Move>();

     BGScrollScript.speed = 0.0f;
     waterScrollScript.speed = 0.0f;
     BGTreeScrollScript.speed = 0.0f;
     FGTreeScrollScript.speed = 0.0f;
     FGCloudScrollScript.speed = 0.0f;
     MGCouldScrollSCript.speed = 0.0f;

     GameObject.FindGameObjectWithTag ("Speed_Part").GetComponent<ParticleSystem> ().enableEmission = false;

 }
 
 // Update is called once per frame
 void Update () 
 {
     
     timer -= Time.deltaTime;
     speed_timer -= Time.deltaTime;

     if (timer <= 0) 
     {
         
         BGScrollScript.speed = 0.02f * speed;
         waterScrollScript.speed = 0.09f * speed;
         BGTreeScrollScript.speed = 0.05f * speed;
         FGTreeScrollScript.speed = 0.09f * speed;
         FGCloudScrollScript.speed = 0.027f * speed;
         MGCouldScrollSCript.speed = 0.021f * speed;
         knifeTween.startMove = true;
         GameObject.FindGameObjectWithTag ("Speed_Part").GetComponent<ParticleSystem> ().enableEmission = true;
     
     }

     if (speed_timer <= 0) 
     {
         if (speed > 0) {
             speed -= 0.1f;
             speed_timer = reset_speed_timer;
         }
     }


 }

}

The problem is everytime my speed decreases by 1 the background kind of jumps instead of doing it smoothly. I tried changing the Time.Time to Time.deltatime and my background doesn't even move period. Any help would be appreciated to pointing me in the right direction.