How do I make an empty TextBox stretch vertically?

I want to make a ListBox that arranges items horizontally. Each item should be a TextBox, and it should fill the list box vertically regardless how how much text is there. If you've used Tweetdeck, I'm aiming for a similar effect. Here's what I've got: ``` <ListBox Background ="DarkGray" ScrollViewer.HorizontalScrollBarVisibility="Auto" ScrollViewer.VerticalScrollBarVisibility="Disabled" ItemsSource="{Binding Path=Items}"> <ListBox.ItemsPanel> <ItemsPanelTemplate> <DockPanel IsItemsHost="True"/> </ItemsPanelTemplate> </ListBox.ItemsPanel> <ListBox.ItemTemplate> <DataTemplate> <Border BorderBrush="Gray" BorderThickness="2" CornerRadius="5" Margin="2,0,2,0"> <Grid Width="250"> <Grid.ColumnDefinitions> <ColumnDefinition Width="*" /> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="*" /> </Grid.RowDefinitions> <TextBox Grid.Row="0" Grid.Column="0" VerticalAlignment="Stretch" Text="{Binding Path=Messages, Mode=OneWay}" /> </Grid> </Border> </DataTemplate> </ListBox.ItemTemplate> </ListBox> ``` What happens is that the TextBox stubbornly fits the text in it, rather than stretching vertically. I've tried switching the Grid for a DockPanel, which didn't help. I could bind the TextBox's Height property, but that seems unpleasant. Is there a trick to this that I've missed?