Thank you for providing this service.
I live in Markham, climate zone 6a with clay soil. The hostas in question are under a black walnut, so the area is currently sunny, but will be shady once the tree’s leaves come out. The hostas have grown successfully in this location for about 5 years.
I have 9 hostas that are in various stages of rotting and few others that I am not sure about yet. After some internet research I have come upon 2 potential causes, one being petiole rot caused by the fungus Sclerotuim rolfsii var. delphinii, and the other being caused by freezing temperatures after the hosta has become active. Fearing fungus, I have removed the plants from the garden, but if there is a simpler explanation I’ll put them back.
The only work I have done in that area of the garden this spring is to clean it up and spread CIL Biomax Composted Manure on top of the soil and around any shoots that were visible at the time.
I have attached a file showing one of the hostas. Please let me know the cause of this problem and what I should do about it.
Thank-you for contacting Toronto Master Gardeners with your question.
Hostas are such robust plants, it is hard to imagine them succumbing to frost, but it does happen! I think this is the more likely scenario in your case. Crown rot caused by Sclerotium rolfsii tends to occur in warm, humid weather conditions, quite unlike what we have been experiencing in Toronto until the last day or so. The yellowing of the leaves also seems to be a different symptom than you are seeing with your hostas. Take a look at the article below for more on this disease:
Some hostas push up their new growth as leaf “bullets” quite early in the season, and we did experience a fairly hard frost well into May. Assuming that it is frost damage, you can cut away the rotted foliage and replant your hostas. They really are very tough plants and will begin to grow new leaves. If the damage has been extensive, they may be a little less vigorous than other years, but they should survive.
Good luck with your hostas!