how to search between two date range

 This is my table in db

create table gridview(id bigint identity(1,1),name varchar(65),startdate varchar(1000),enddate varchar(1000),gender char(25),mobileno bigint,designition varchar(100),
					  country nvarchar(65),state nvarchar(65),city nvarchar(65))

i want to write a procedure  for from date to to to date 

once i click on button it should display only records between the two dates only pls help me

This is my procedure

create PROCEDURE sp_SearchCustomerDetailsByDate
    @StartDate varchar(100),
    @EndDate varchar(100)
AS
BEGIN
select * from gridview where startdate between @StartDate and  @EndDate
END

This is My code  for getting date

private DataTable GetDate(string fromdate, string enddate)
{
    using (SqlCommand cmd = new SqlCommand("sp_SearchCustomerDetailsByDate", con))
    {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@StartDate",fromdate);
        cmd.Parameters.AddWithValue("@EndDate",enddate);
        using (SqlDataAdapter da = new SqlDataAdapter(cmd))
        {
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
    }
}

This is my button1click code 

protected void Button1_Click(object sender, EventArgs e)
{
    DataTable dt = GetDate(TextBox12.Text,TextBox13.Text);
    this.GridView1.DataSource = dt;
    this.GridView1.DataBind();
}

pls help me out