TextBlock scroll is not working in WPF

I want to make my TextBlock scrollable but I can't make it work. Maybe problem is in StackPanel?

So here is the code:

 <Grid Margin="3">
        <Grid.RowDefinitions>
            <RowDefinition Height="152*" />
            <RowDefinition Height="86*" />
            <RowDefinition Height="67*" />
        </Grid.RowDefinitions>

        <ListBox x:Name="lstItems" Margin="3,6,3,0" ItemsSource="{Binding Source={StaticResource rssData}}"
                 SelectedIndex="0">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Image Width="20" Margin="3" Source="{Binding XPath=enclosure/@url}" />
                        <TextBlock Margin="3" VerticalAlignment="Center" Text="{Binding XPath=title}" FontWeight="Bold" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <StackPanel Grid.Row="1" Orientation="Vertical" DataContext="{Binding ElementName=lstItems, Path=SelectedItem}" Grid.RowSpan="2">
            <StackPanel.ScrollOwner>
                <ScrollViewer />
            </StackPanel.ScrollOwner>
            <TextBlock Margin="3" FontSize="13" FontWeight="Bold" Text="{Binding XPath=title, Path=InnerText}" />
            <TextBlock Margin="3" Opacity="0.72" Text="{Binding XPath=pubDate}" />
            <ScrollViewer>
                <TextBlock ScrollViewer.CanContentScroll="True" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto" Margin="3" FontStyle="Italic" Text="{Binding XPath=description, Path=InnerText}" TextWrapping="Wrap" TextAlignment="Justify" Height="216" Width="489" AllowDrop="False" Foreground="#FF0000E7" FontFamily="Lucida Sans Unicode" />
            </ScrollViewer>
        </StackPanel>
    </Grid>

Problem is in this part:

<ScrollViewer>
             <TextBlock ScrollViewer.CanContentScroll="True" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto" Margin="3" FontStyle="Italic" Text="{Binding XPath=description, Path=InnerText}" TextWrapping="Wrap" TextAlignment="Justify" Height="216" Width="489" AllowDrop="False" Foreground="#FF0000E7" FontFamily="Lucida Sans Unicode" />
</ScrollViewer>

This part of the code should be able to scroll. I can see vertical scroll bar but can't scroll. I want to be able to see in StackPanel as I am not allowing any changes and want read only.

Thank you

EDIT:

<Window x:Class="RssDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="RSS Demo" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" Height="576" Width="521">
    <Window.Background>
        <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
            <GradientStop Color="#FFE2E2E2" Offset="0" />
            <GradientStop Color="White" Offset="1" />
        </LinearGradientBrush>
    </Window.Background>

    <Window.Resources>
        <XmlDataProvider x:Key="rssData" XPath="//item" Source="http://www.hak.hr/rss/stanje/hr.xml" />
    </Window.Resources>

    <Grid Margin="3">
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <ListBox x:Name="lstItems" Margin="3,6,3,0" ItemsSource="{Binding Source={StaticResource rssData}}"
                 SelectedIndex="0">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Image Width="20" Margin="3" Source="{Binding XPath=enclosure/@url}" />
                        <TextBlock Margin="3" VerticalAlignment="Center" Text="{Binding XPath=title}" FontWeight="Bold" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <StackPanel Grid.Row="1" Orientation="Vertical" DataContext="{Binding ElementName=lstItems, Path=SelectedItem}">
            <TextBlock Margin="3" FontSize="13" FontWeight="Bold" Text="{Binding XPath=title, Path=InnerText}" />
            <TextBlock Margin="3" Opacity="0.72" Text="{Binding XPath=pubDate}" />
        </StackPanel>
        <ScrollViewer Grid.Row="2" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">
            <TextBlock ScrollViewer.CanContentScroll="True" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto" Margin="3"
                       FontStyle="Italic" Text="{Binding XPath=description, Path=InnerText}" TextWrapping="Wrap" TextAlignment="Justify" Width="489" AllowDrop="False"
                       Foreground="#FF0000E7" FontFamily="Lucida Sans Unicode" />
        </ScrollViewer>

    </Grid>
</Window>

Paste this code to your project as this is with the rss link where I read info. Just to see what you will get

Solution

Here's what I had to do, hopefully you can do the same. First I had to place the ScrollViewer around the StackPanel and then I had to remove the Height from the TextBlock.

     <ScrollViewer HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">   
        <StackPanel Orientation="Vertical">
           <TextBlock Text="Test" />      
           <TextBlock x:Name="test" Margin="3" FontStyle="Italic" VerticalAlignment="Stretch"
                      TextWrapping="Wrap" TextAlignment="Justify" Width="489" AllowDrop="False" Foreground="#FF0000E7" FontFamily="Lucida Sans Unicode" />      
        </StackPanel>
     </ScrollViewer>

EDIT

    <Grid Margin="3">
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <ListBox x:Name="lstItems" Margin="3,6,3,0" ItemsSource="{Binding Source={StaticResource rssData}}"
                 SelectedIndex="0">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Image Width="20" Margin="3" Source="{Binding XPath=enclosure/@url}" />
                        <TextBlock Margin="3" VerticalAlignment="Center" Text="{Binding XPath=title}" FontWeight="Bold" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <StackPanel Grid.Row="1" Orientation="Vertical" DataContext="{Binding ElementName=lstItems, Path=SelectedItem}">
            <TextBlock Margin="3" FontSize="13" FontWeight="Bold" Text="{Binding XPath=title, Path=InnerText}" />
            <TextBlock Margin="3" Opacity="0.72" Text="{Binding XPath=pubDate}" />
        </StackPanel>
        <ScrollViewer Grid.Row="2" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">   
            <TextBlock Margin="3"
                       FontStyle="Italic" Text="{Binding XPath=description, Path=InnerText}" TextWrapping="Wrap" TextAlignment="Justify" Width="489" AllowDrop="False" 
                       Foreground="#FF0000E7" FontFamily="Lucida Sans Unicode" />      
         </ScrollViewer>        

    </Grid>

Some things to point out...I modified your Grid Row Heights. * is used to denote fill and the number does not mean pixels. So what you hd=ad does not behave like a min with resize. Essentiall 187* does not mean a greedy 187 pixels, where the space is at least 187 pixels but will grow as needed. Setting the three row heights to * as I did above simply gives them each a 3rd of the parent height. If you want the 2nd row to be twice as large as the others, set the others to * and set the middle row to 2*. Since I can't see your screen, you can adjust as needed. You may also be interested in using Auto and size it to the content.

Here's a screenshot of it working for me: Scrollable TextBlock