Ion-row doesn't take height of ion-grid

According to the docs it says:

By default, columns will stretch to fill the entire height of the row

It seems that I can only “play” with the grid / columns, but what makes the row to fill the entire hight of the grid ?

It’s great that the column can be 100% the row - but how can I control the row’s height ?

This doesn’t work for me:

 ion-grid {
        height: 100%;

        ion-row {
            flex: 1;