Thursday, January 6, 2011

Three aeoniums

Aeoniums are subtropical succulents native to the Canary Islands off the northwest coast of Africa. There are 35 species, including the tree aeonium (Aeonium arboreum) which can grow to 6 ft.

Aeoniums are members of the Crassulaceae family which also includes many other rosette-forming succulents such as echeverias, graptopetalums and dudleyas. Sometimes it is hard to keep them all apart, but in general, the leaves of aeoniums are less fleshy that those of other crassulaceaes. In addition, most aeonium species have strong stems that keep the rosettes upright. In contrast, many other crassulaceaes are stemless or have short, weak stems so the rosettes are packed together quite tightly and/or are close to the ground.

Like most agaves and some other succulents, aeoniums are typically monocarpic. This means that the rosette will die after flowering. This is not a big deal for multi-branched aeoniums with many rosettes, but if a plant only has one rosette, the whole plant will perish. (Most aeoniums take 5 years or longer to flower so you get quite a bit of enjoyment out of your plant.)

Coming from a Mediterranean climate where most of the precipitation falls in the winter, aeoniums are winter growers and go semi-dormant in the summer. This means that they need regular water in the winter, less in the summer. In coastal climates, the humidity in the air is often all the moisture they need. In drier inland areas, weekly summer watering is advised if your goal is to grow the nicest looking plants possible. A couple of years ago, I neglected my potted Aeonium undulatum (saucer plant) for almost an entire summer; the only water it received was overspray from a nearby lawn sprinkler. While it looked a bit ratty, it hung on quite valiantly and began to perk up as soon as I began to water it more frequently. Today it looks as good as it ever has (see photos below).

As far as soil goes, aeoniums are not picky. They tolerate more water than many other succulents and accept somewhat heavier soils without rotting. Heavy clay still spells doom, however, as it does for so many plants. In pots, I would recommend a good general-purpose potting soil instead of the specialty soil sold for cacti and succulents since aeoniums don’t like it bone dry.

In many respects, aeoniums are the perfect plants for busy gardeners. They are undemanding, not prone to pests, and add a touch of the exotic. However, they are not cold hardy. They tolerate a light freeze, down to 28° or so, but go to mush in temperatures much lower than that. Provided the freeze is only short-lived, they usually come back fairly quickly. Even so, if you live in USDA hardiness zone 9a or below, I recommend you plant your aeoniums in pots and bring them inside for the winter. They prefer bright light so a place by a window would be ideal.

In our garden, we currently have three aeoniums. One is planted in the ground, the other two are in pots on our front porch.

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Two potted aeoniums: Aeonium haworthii ‘Kiwi’ on the left and Aeonium undulatum on the right, with a dwarf aloe and an echeveria hybrid in between

Aeonium undulatum, also known as “saucer plant”, can grow up to 3 ft. tall. Most plants are single-stemmed, but others (like ours) branch at ground level and therefore have more than one rosette. The rosette on a mature plant can be 12"-16" across. The largest rosette on our 3-year old potted plant is currently 8" across.

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Perfect rosette on our potted Aeonium undulatum
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Two members of the Crassulaceae family: Aeonium undulatum (right) and Echeveria hybrid (left)

Aeonium haworthii ‘Kiwi’ has a creamy center that becomes progressively greener toward the outside of the rosette. Our plant is grown in bright indirect light; in the sun, you’d see a pink margin around the leaves. The more sun, the more pronounced this margin becomes. I actually prefer it without the pink margin.

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Potted Aeonium haworthii ‘Kiwi’, grown in the shade. The rosette is 5" across.

Aeonium arboreum ‘Atropurpureum’ is a purple-leaved tree aeonium. Ours grows in the succulent bed next to our driveway. This location is in partial shade, which is why the leaves are less purple than they would be in full sun. Some cultivars of Aeonium arboreum, especially ‘Zwartkop’, are such a deep purple that from a distance they appear black.

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Aeonium arboreum ‘Atropurpureum’, planted in the ground. It survived last winter’s 26°F low with no damage.

These three aeoniums, and some others, are commonly available in all nurseries and box store garden centers. Rarer species and hybrids can be obtained from specialty succulent nurseries.

3 comments:

  1. Great read Gerhard, provides a really good insight into this fantastic group of succulents.

    It's true that they are an undemanding group of plants. They actually look better in manicured gardens as opposed to the ones naturalised in the wild, including the Canaries.

    My favourite is the A. undulatum and the cultivar Zwartkop.

    I had my Aeonium phase before too and collected several but I have curbed that now mainly due to lack of time and just sticking with a few of them now, used as a summer display as non of them are hardy enough for our location.

    Are you planning to expand your collection too? They'd look fab in your yard :)

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  2. Mark and Gaz, I must say I hadn't been paying too much attention to our aeoniums until somehow the potted ones on the front porch caught my attention the other day and I saw how absolutely beautiful they were.

    I'm now looking for a larger Zwartkop to add to my collection. There are very few plants that offer that kind of deep purple. I bought an awesome golden barrel cactus the other day (post to follow on Monday) and I think Zwartkop would look stunning right next to it.

    Unfortunately, aeoniums are not 100% hardy here. They do fine most winters but every few years a night or two of 25°F (-4°C) knocks them back. San Francisco and the coastal regions south have the perfect climate. Coastal Southern California can't be beat as far as tender succulents go.

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  3. No chance for any Aeonium to survive outside here during winter :(

    If I remember correctly, there are at least two other purple Aeoniums that get bigger than Zwartkop, they are Voodoo and Cyclops.

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