- Author: Jane Callier
Research showed that "dark spots on succulents” yielded that initial likely suspects included physical injury, sunshine, insect activity, fungal infection and too much water. Fungus? Insect activity in the middle of winter? It certainly hadn't been sunny, either, which left "too much water" as the strongest candidate as the cause of the problem. A look in UCANR publication 3420, Abiotic Disorders of Landscape plants, offered some information about edema. Following a trail of virtual bread crumbs supported this idea. The description of ‘brown, corky spots on the leaves' fit the bill, and the diagnosis of edema made a lot of sense.
Edema, the abnormal retention of water, can be caused by water intake through the roots that outstrips the plant's rate of transpiration. Given that the one condition that has changed most markedly on our patio this past year is the amount of rainfall, the obvious conclusion is that the succulents have been struggling with too much water. Succulents do best when their soil is allowed to dry between waterings.
The good news is that mildly affected plants can recover from edema. New growth started in late spring is a signal of recovery. We've had a few sunny warm days, the soil had dried and the plants appeared to be on the mend, but now we've been hit with more big rainstorms. The plants will survive this, too. Just another testament to the hardy character of succulents.