making grass move at different speeds

Hi! I'm using the atsGrass-Unlit-Wind Shader for making grassplanes move as in the wind. The planes are being instantiated as I press play, every plane has it's WindShader script where I set a random Value to the windforces and set that value to the shader. If I select any plane, the values will therefore be different, but the planes still move all at the same speed. Does anybody know, why that could be?

Here is the shadercode:

 // - Unlit
 
 Shader "GrassShader" {
 Properties {
     _MainTex ("Base (RGB) Alpha (A)", 2D) = "white" {}
     _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
 }
 
 SubShader {
     Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" "LightMode"="ForwardBase"}
     LOD 100
     Cull Off
     ZWrite Off
     Blend SrcAlpha OneMinusSrcAlpha 
     
     
     CGINCLUDE
     #include "UnityCG.cginc"
     sampler2D _MainTex;
     half4 _MainTex_ST;
     
     float4 _GrassWind; //is not defined in terrainengine.cginc
 
     struct v2f {
         float4 pos : SV_POSITION;
         float2 uv : TEXCOORD0;
     };
 
 inline float4 AnimateGrass(float4 pos, float3 normal, float animParams)
 {    
     // animParams stored in color
     // animParams = primary factor = blue
     // Primary bending
     // Displace position
     pos.xyz += animParams * _GrassWind.xyz * _GrassWind.w; // controlled by vertex color blue
     return pos;
 }
 
 
     
     v2f vert (appdata_full v)
     {
         v2f o;
         float4    windParams    = float(v.color.b);        
         // call vertex animation
         float4 mdlPos = AnimateGrass(v.vertex, v.normal, windParams);
         o.pos = mul(UNITY_MATRIX_MVP,mdlPos);
         o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
         return o;
     }
     ENDCG
 
     Pass {
         CGPROGRAM
         #pragma debug
         #pragma vertex vert
         #pragma fragment frag
         #pragma fragmentoption ARB_precision_hint_fastest        
         fixed4 frag (v2f i) : COLOR
         {
             fixed4 tex = tex2D (_MainTex, i.uv);
             
             fixed4 c;
             c.rgb = tex.rgb;
             c.a = tex.a;
             
             return c;
         }
         ENDCG
     }    
 }
 }

and here is the script:

 using UnityEngine;
 using System.Collections;
 
 public class WindShader : MonoBehaviour 
 {
     public Color VertexLitTranslucencyColor;
     public Vector4 Wind;
     public float GrassWindFrequency;    
     
     void Start ()
     {
         Wind = new Vector4 (UnityEngine.Random.Range (0.5f, 1.5f), 0, 0, UnityEngine.Random.Range (0.5f, 1.5f));
         VertexLitTranslucencyColor = new Color (UnityEngine.Random.Range (0, 1), UnityEngine.Random.Range (0, 1), UnityEngine.Random.Range (0, 1), UnityEngine.Random.Range (0, 1));
         GrassWindFrequency = UnityEngine.Random.Range (1, 2);
         
         Application.targetFrameRate = 100;
         
         Shader.SetGlobalColor("_TranslucencyColor", VertexLitTranslucencyColor);
         Shader.SetGlobalFloat("_TranslucencyViewDependency;", 0.65f);
         Shader.SetGlobalFloat("_ShadowOffsetScale;", 1.0f);    
     }
     
     
     void Update ()
     {
         Shader.SetGlobalColor("_GrassWind", Wind);
         Color GrassWindRGBA = Wind *  ( (Mathf.Sin(Time.realtimeSinceStartup * GrassWindFrequency)));
         GrassWindRGBA.a = Wind.w;
         Shader.SetGlobalColor("_GrassWind", GrassWindRGBA);
     }
 }