Conventional seasonal care advice for aeoniums is to "withhold summer water," info I've routinely passed along. But it's always bothered me. My own experience and observations indicate otherwise.
For over 20 years, I've cultivated a dozen or more types of Aeonium
in my garden NE of San Diego.
It's Zone 9b---dry inland foothills with a slight maritime influence. Summer rainfall is seldom and temps soar into the triple digits from late-August through mid-September.
Above: Aeoniums thrive in dappled shade in my garden. Center: A. urbicum. In back: A. 'Sunburst'. Far right: dark A. 'Zwartkop' and below it, A. 'Kiwi'. Variegates can be susceptible to sunburn. Darker aeoniums fare best; more pigment = better sun protection. Learn more on my Aeonium page.
The genus Aeonium is native to the Canary Islands off northwestern Africa, where the climate is among the best in the world. Temps are mild year-round and days sunny. Rain is minimal and falls December through February. If that sounds familiar, it should: It's similar to coastal CA from the Bay Area south.
It seems counterintuitive, but...
Aeoniums don’t do well in other "ideal" US climates like Hawaii and Florida. The reason is those regions' heavy summer rains and humidity. If aeoniums sit in soaked soil and and stay damp, stems and roots rot---especially if the plants are dormant.
However in CA, where rain falls mainly in winter and humidity is low, rot is unlikely even after drenching winter rains.
When you should do something
I lazily leave aeoniums alone unless I want to snip cuttings or to redo an overgrown bed (every 3-4 years).
What does kill aeoniums
Seems the only thing that kills these super-easy succulents is flowering. After individual rosettes elongate into bloom, they'll die (i.e. they're “monocarpic.”)
Not all rosettes in a colony bloom at once, and it takes years for most aeonium rosettes to flower. Enjoy the show, then cut the stalks where they join the trunk.
True, aeoniums that get no water look like they're at death’s door by September…which is when my neighbors’ gardener yanks theirs. Oh, if he'd only wait! Aeoniums that appear moribund will bounce back in a few months!
The bottom line
The conclusion I've come to is that if you're in CA, you can choose whether or not to water your aeoniums. Those of mine that get irrigated along with everything else look fine all summer. I don't water those that have gone dormant.
But how to tell if an aeonium is dormant?
If you're wondering how to tell if an aeonium has gone dormant, because you're worried you'll overwater it, no worries. It's a non-issue. Growth does slow after the spring spurt, but you can safely assume that aeoniums that are getting regular water and look healthy are perfectly fine.
As for my no-water ones---those beyond the irrigation system---they begin losing their sheen in July. By end-August, leaves have shriveled, and rosettes resemble closed purses. This smart, moisture-saving tactic reveals naked stems, which make plants look truly sad.
My Aeonium haworthii in September, after six months with no water.
The same aeonium in the spring, after winter storms. This drought-then-flourish cycle happens every year, and the plant keeps getting bigger.
What if you do water them?
So, should you water ratty, sleeping aeoniums in summer? Sure, if you want to. They might not look better afterwards, but it could help keep small, heat-stressed specimens alive---especially those out in the open that are baking in dry, shallow soil. In any case, if they don't sit in water for days, it won't harm them.
And if you don't? Roots may desiccate, but if they still anchor the plant, it'll regenerate new roots during winter rains.
If the roots of a neglected aeonium like this one haven't dried completely, some summer watering will likely hydrate them. But please don't stress over how to tell. It's fine to let sleeping aeoniums lie.
Debra's Seasonal summary for Aeoniums
Note that these changes don't happen overnight. They're so subtle, you may not notice until they're well underway.
In Southern and Coastal CA:
- SUMMER: July-September. Aeoniums begin going dormant as the weather warms. Those that receive no summer irrigation are completely (and clearly) dormant by late-summer heat waves.
- FALL: October-December. Aeoniums begin to awaken as days shorten, temperatures drop and rains return. Now into mid-winter is the best time to take and start cuttings.
- WINTER: December-February. Growing season; aeoniums look better and better. Roots in rain-soaked spread in preparation for fueling spring top growth. Cuttings started in fall root quickly.
- SPRING: March-June. Few succulents are so lush and lovely as rain-revived aeoniums. Spring is when they flower, so do enjoy the show. Deadhead spent blooms to keep the plants tidy.