I had 4 knockout roses and the last time that I cut them back 3 of them died. Would it be safe to replant knockout in that same area?
Severe pruning in late summer, early to mid fall is a serious mistake. However, pruning roses shouldn't kill them, especially the hardy Knock-Outs. If you live in a region that has severe winters, I wonder if having them on a small berm is subjecting the crown and roots to killing temperatures. I wish I knew where you live and what happened exactly. Did they never leaf out after dormant season pruning? When you dug them out did you notice insect or grub activity in the canes or on the roots. Were the roots rotten and soft? I think I see landscape fabric. I suggest you remove it so each rose has a minimum of 4 ft of fabric-free access to water and nutrients. Despite how it is advertised, landscape fabric only lets some water and air through; on the slight hill you have, a lot of water will run off before soaking into the soil. And plant roots need oxygen; fabric restricts air penetration. And it doesn't prevent weeds anyway, as many of us have discovered. I would not plant until I was sure what happened to the plants that died. If you wish to add further information, we'll see if we can provide further help.