I'm a complete gardening novice but luckily 2 years ago we moved into a house where the previous owners were quite good gardeners.
Back garden is traditional flower beds and lawn. The flower beds have bark chippings between the plants. But we have 2 cats and after 2 years of the using the flower beds as a giant cat litter tray, the chippings need renewing/topping up.
It is recommended to remove all the old chippings before putting new ones down or can I just top up? Also, would there be any benefit from lightly digging over the flower beds before putting the new bark chippings down? Finally, is there a formula to work out how many bags of chippings I need to get? I've estimated the flower bed area to be 150 sq feet.