For the default value, add it in the model. Maybe in an after_initialize callback. For the row and col values, read the documentation. http://api.rubyonrails.org/?q=text_area
Hey
If you want default values add them in your model. If you are talking about a placeholder in your view:
form_for() do |f|
f.text_area :name, :rows => 5, :placeholder => "Your Text here...."
AS you can see i set 5 rows for the text area AS default to display. And there is some placeholder text in it...
Hope this helps you.