I have a shaded woodland garden in downtown Toronto. I have Hostas along a shady path, some growing in Vinca, some in loam beds. A number of new Hosta shoots have not unfurled and grown misshapen with the very tip drying to a black kind of thread. What can cause this? I have included a photo of H Royal Standard deformed shoots.
The likely culprit is frost, which has so recently left the Toronto area!
The Missouri Botanical Garden’s Hosta Problems sets out a number of pests, diseases and even damage from adverse weather conditions that can affect these plants. It’s now May 30 2020 and frost was a concern in the Toronto area until a few days ago. Frost kills the plant tissues that are actively growing, so newly emerging leaves will be missing tissue and have browned or blackish areas – note that if frosts are severe, plants may be limp, blackened and distorted or misshapen.
See also a post from last week on the Ask a Master Gardener website, Hostas going mushy, which suggests that frost was the cause of a similar issue with someone else’s hostas.
The best option would be for you to simply leave the plants alone – they are very resilient and should bounce back as the spring/summer progresses. If you don’t like looking at the misshapen leaves, cut the worst of them away and watch for the healthy new shoots to emerge.