We often hear or read that cactus & succulents go dormant in the summer. How true is this statement? How do we prove this statement? One way is to find out through first-hand experience.
In my limited experience in keeping plants over a few summers in Phoenix, Arizona, I have found that some but not all succulents go dormant in the summer. And our summers are extreme with weeks in a row with overnight lows above 80F. I have lost many Aloe and the colorful soft-leafed succulents like Echeveria and Crassula due to unintentional watering due to ignorance, or later on, accidentally watering while dormant, which is why I've been avoiding adding them to my plant family. On the other hand, Agaves have always fared well in the summer - I water them once a week and they do great. I have not found Ariocparpus nor Astrophytum to go dormant in the summer here. They dry out quickly, show signs of thirst and plump up after being watered deeply. Heck, some Astrophytum are still in bloom here!
I have also found Saguaro, Ferocactus, Melocactus, Matucana madisoniorum, Gymnocalycium, Trichocereus, Myrtillocactus, Thelocactus among others to do fine with regular waterings in the summer despite the heat.
Mammillaria I tend to water more conservatively during the summer and in general. I do this not necessarily because I think they go dormant. I do so because they seem to do exceptionally well at conserving water.
Now when it comes to Copiapoa, summer dormancy is still up in the air. This is my seedlings' first summer outdoors so it's too soon to say. I have a handful of mature plants that have survived our summers here so far. I have one Copiapoa esmeraldana that has survived several summers with me with regular watering. Perhaps some Copiapoa go dormant in the summer but maybe not ALL Copiapoa go dormant in the summer. But I cannot say any of this with any certainty - I need more summers under my belt before I can make any conclusions.
Do keep in mind that the plants I listed are very limited. I own only so many genera of plants and I cannot make any statements on any plants that I've never grown before. That's where the plant community is extremely important - a collective knowledge of experience.
What is your experience with plant summer dormancy? Which plants have you seen first-hand do well or poorly in the summer heat? Please leave a comment on your experience and include your climate conditions - this will be a huge help to me and anyone else reading the comments section.
Stay cool, my cactus friends!
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