What: Forms where supercooled liquid water droplets freeze on contact with cold surfaces. (If vapor goes from gas to solid, it’s hoar frost; from liquid to solid, it’s rime.)
Why: Happens when a freezing fog or glaze forms as a continuos thick layer of ice, rather than individual frozen droplets.
What to do: Discontinue fertilizing in early September, so there’s no tender new foliage on the plant when the cold temperatures arrive. When frost is forecast, water the garden thoroughly before nightfall, cover as much as possible with sheeting, and wrap containers in a thick coat of burlap.