These rosette succulents from the Canary Islands are popular garden plants in arid climates, providing color accents (especially red, purple, and yellow) that vary with the passage of the seasons. Aeoniums make excellent container plants in less forgiving climates, though they require a lot of light indoors. Most of the plants in cultivation are hybrids and cultivars, rather than species (which total about 40, depending on how you count).
The most common plants in cultivation tend to branch freely and make excellent beginner propagation subjects. Each rosette will flower after a few years with an elaborate burst of yellow, white, pink, or rarely red flowers, and then die, leaving any other branches to live on. Only one Aeonium (simsii) makes a lateral inflorescence which does not result in the death of the rosette. Aeonium flowers usually make a dramatic statement in the garden and often attract bees.
It can be difficult to identify most random Aeoniums in cultivation. On top of the considerable variation within a species, any given plant can be incredibly different in size and appearance depending on the season, the exposure, the care, and the container. And most plants in cultivation are not species but hybrids or cultivars.
The fine marginal hairs which decorate most Aeonium leaves are a useful feature to distinguish them from other similar-looking rosette succulents from the New World, like Echeverias. Aeoniums typically have thinner leaves, with two exceptions: sedifolium and nobile, which also lack marginal hairs but may have tiny bumps instead. Most Aeonium species (except tabuliforme) grow a stem, which may reach up to 1m tall, and when they flower the distinctive cone or mound-like inflorescences give away the genus. Plants which are kept constrained and pot-bound will be smaller, branchless and take longer to flower.
Other features which can be used to identify Aeonium species include the surface texture of the stem (which may be flaky, smooth, fissured, or hairy) and the texture of the leaves (which may be smooth, sticky, or fuzzy). Some leaves may have water-storing idioblasts on the underside, others may have tannic stripes on top.
Aeoniums benefit from typical succulent care, including strong light, regular water when the soil is going dry, and good drainage. They do not demand a lot of space in pots, but the larger plants do appreciate some extra room, and one Aeonium (nobile) gets large enough to become impractical in most containers.
Aeoniums also suffer from the same insect pests that affect other succulents, including mealybugs (which hide out at the base of leaves, close to the stem near the growth points) and aphids (found in a similar location or at the center of the rosette). The latter is particularly problematic during flowering. Look for ant traffic as a sign of infestation. Aeonium flowers tend to be bug magnets in the patio or container garden; this behavior is greatly reduced by natural predation in the landscape.
Aeoniums are delectable to most herbivores, including mammals (squirrels, rabbits, livestock), especially when newly planted and during times of drought, since the succulent leaves store water.
The plants which branch are usually very easy to start from cuttings taken just below a terminal rosette.
The Canary Islands have a Mediterranean climate with wet winters and dry summers, and this pattern helps explain the behavior of Aeoniums in cultivation.
It is important to understand and respect this annual cycle, which may be exaggerated by summer heat and exposure, especially in marginal (hot) climates. Despite their appearance in summer, Aeoniums do not need extra water at this time. On the flip side, during the period of active growth, which coincides with the darkest days of the year, it is important to provide strong light. Indoor Aeoniums usually require hours of daily sun during this period.
Aeoniums are mostly from the Canary Islands, but 6 species occur elsewhere.
Aeonium is related to Sempervivum and various other succulent genera in the Crassulaceae, most closely to Greenovia, Aichryson, and Monanthes, which overlap in distribution. Greenovia has at times been merged with Aeonium.
Joel Lode, Succulent Plants of the Canary Islands, 2010
Rudolf Schulz, Aeonium in Habitat and Cultivation, 2007