Strange fungus/mould


Hi Master Gardeners

I have a smallish garden bed, part of a small deco outside my kitchen. It is planted with climbing hydrangeas.

A couple of weeks ago I put some cacao bean shell mulch (from Chocosol here in TO)
on n top of the soil here. This has managed to stop the squirrels from digging out to the roots but yesterday I noticed that the soil area was covered with these fine fungus (?) threads

It has been wet & humid recently. I don’t know if this explains what has happened. Do you think something was already in my soil or perhaps this came from the cacao shell mulch?

The soil is an AllTreat Multiblend (bought at Fiesta Gardens nearby.

The area is not full sun but partial – full in the mid to later pm

Thank you!


Thank you for contacting Toronto Master Gardeners.

The white fungus you observe is caused by some species of the fungus Sclerotinia. During periods of cool, wet weather, such as your recent weather, the fungus establishes itself.

The origin of this mold could well be the cacao bean shell mulch you applied recently. The fungus overwinters in dead plant material and can survive in the soil for several years.  Sclerotinia infection often begins on dead or decaying plant parts like flowers and leaves, and then spreads to healthy tissue.

The safest course of action to address this fungus problem is to immediately remove any plants, organic matter and soil that show signs of the fungus. Do not put this material on your compost pile – either bury the infected items in an area of the yard that will not be used for vegetable or flower gardening in the future, or put them in municipal yard waste.

To lessen the chance of this happening again, do not overwater the area, and make sure it has good drainage. In the fall, remove any plant debris from the area, including roots.

Good luck with your gardening.