I'm stumbling on "It appears there is too much water in the containers. There is more than adequate drainage"....the two don't go together :) We've had one dry day in the last 23 here, I wouldn't be adding water but I don't have anything too soggy either. A little moss and liverwort (hate that stuff) beginning on a few that have been sown since Fall but no algae or mold/mildew. Are you sure about the drainage holes? If you had a way of letting more ventilation in it would probably take care of the white fuzzies. I'd open them up more if mine, but I've only dealt with the over night temps you say you are having 3 times this season and only for a few nights in a row each time...pots were covered just for the duration of those cold fronts/storms. My climate doesn't lend itself to having to deal with the hard overnight freezes as a nightly routine, but I do know the white fuzz means moisture and no air movement.

Judy, the foam protects them from any chemical you might use. If your hydrangea is the size you describe, you can spray away the foam with water, or take a paper towel, wipe them off and squash. You're going to find a little green to yellow-green soft nymph inside the foam. The nymph is sucking sap, causing the distortion. And when you're done with your hydrangea, you can come and do my lavender - they are covered this year, along with the hardy fuchsias :)

Can't see much detail in your small photo. But most likely, it's a mold degrading the organic stuff in the potting mix. So, not to worry; it won't affect your plant.

the link says: A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant. In a mycorrhizal association, the fungus colonizes the host plant's roots, ==>>> as far as i know.. its beneficial.. and encouraged.. as far as peeps buying it.. and adding it to the soil ... panicking and bleaching it all away.. was probably not a good idea ken Here is a link that might be useful: link