I bought 13 dahlias from the same supplier and planted them in a row to form an informal hedge in front of an evergreen hedge in a new garden bed. Two of the dahlias didn't come up and when I investigated them today I discovered nothing but mush and slime where the tubers used to be. I will now have two gaping holes in my lovely display, which I'm not thrilled about, and I don't know whether I can plant anything in those spots in case the problem infects the new plants too. Does this rot hurt other plants too? I also would like to keep the other tubers in the ground over winter as the ones I left last season all came back up without a problem and I'm lazy enough to not want to dig every year. Would the soil either side of the slime be contaminated? Can I ever plant new dahlias in those places or will the holes be tainted forever?

I've not had issue with rotting tubers and planting new in its space. If everything is still young pick up another tuber or two locally as they'll catch up quickly. Sometimes those that rot weren't great in the first place and it's like everything else in the survival of plants some are healthy and some sketchy.

Thanks for the advice ScarletTricycle.

You're welcome! Post photos as they bloom I think winter will be long for us and we love seeing blooms.