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4 Sept 2020

A glimpse into plant evolution through aeoniums

Written by Kevin Doidge, First Gardener, Inverewe
A smiling man is standing in a glasshouse next to a group of succulent plants.
Inverewe’s First Gardener, Kevin Doidge, with some of the amazing specimens in the National Collection of Aeoniums
Climate change is having an increasing impact on gardens, including Inverewe, and the chances of having more frequent dry spells over the summer will impact on what plants will flourish. Aeoniums are the perfect candidates for this new garden environment.

At Inverewe we hold the National Collection of Aeoniums, a group of succulent plants that are not only visually attractive but tell an interesting story of plant evolution.

The Aeonium genus has a disjointed distribution, with the majority of species found in the Atlantic islands of Macaronesia (Canary Islands, Azores, Madeira and Cape Verde), but with two outliers in East Africa and Yemen. They may originally have been more widespread throughout the Mediterranean and North Africa, but desertification and the spread of the Sahara forced the genus to the edges, where the oceanic islands and the mountains of East Africa helped buffer the worst of the changing climate.

The centre of diversity is the Canary Islands – out of 37 species, only 6 are not found there. The Aeoniums of the Canaries give us an interesting glimpse into plant evolution – they are considered to be of similar importance as the finches of the Galapagos Islands. As with Darwin’s finches, Aeoniums are polymorphic, with many growth forms that relate to the type of habitat in which they grow. These habitats are ecologically diverse, ranging from coastal deserts to cloud forests to subalpine mountains.

Aeoniums belong to the Crassulaceae family, which includes other succulent plants such as echeveria, sedum, sempervivum and crassula. They can all be found in garden centres, often as house plants, but increasingly as outdoor bedding plants.

Aeoniums, in particular, have really taken hold with gardeners due to a myriad of new cultivars in varying shades of purple, pink and red. Their distinctive succulent rosettes make them attractive companions to other subtropical bedding plants, such as osteospermums, argyranthemums and gazanias. At Inverewe, you can be see them in the area known as South Africa, next to the walled garden.

Some of the most attractive cultivars at Inverewe are a mix of purples and reds. For instance, Aeonium ‘Darley Blush’ has an attractive pink blush on the soft downy leaves, while Aeonium ‘Cyclops’ and Aeonium ‘Voodoo’ both have darker, purplish foliage. They can only really be told apart from each other as ‘Cyclops’ has glossy leaves while the leaves of ‘Voodoo’ are more matt. Probably the most well-known cultivar is Aeonium ‘Zwartkop’, which has almost black leaves often on tall stems. It works phenomenally well with silvery leaved plants like the tender Plectranthus argentatus ‘Silver Shield’.

Aeonium ‘Firecracker’ is becoming more widely known and has red-tinged narrow pointed leaves – very different to the other cultivars. It can be grown as a front of border bedding plant with the contrasting Aeonium ‘Ballerina’, which has soft, felted, white variegated leaves.

Other attractive cultivars are Aeonium ‘Kiwi’, a colourful shrubby cultivar that develops into small domes with variegated yellow, green and reddish pink leaves, while Aeonium ‘Bronze Medal’ has unusual but attractive bronze-brown leaves on a very compact form.

Close-up of a small, green-leaved succulent plant.
Aeonium ‘Kiwi’

Aeoniums are relatively easy to grow in a garden setting. They will grow in any soil or potting mix as long as it’s well drained and not too acidic or alkaline. Soil conditions do have an effect though – if they’re grown in very poor soils, they will be smaller and more stunted, but with more intense colouration, stronger stems and larger root systems. In richer soils they will grow quickly and lush with brittle stems and a weaker root system, which is more prone to breaking.

Unlike a lot of succulents, aeoniums are heat-sensitive and don’t like temperatures above 40 degrees, but can cope with increased watering or rainfall, so they seem to be very happy with our wetter and cooler summers here at Inverewe. We usually plant them out after the risk of frost at the end of May and lift them for winter storage in October to protect them from any very cold weather.

Most aeonium species are damaged by frost, but usually recover if temperatures don’t fall below zero for any significant time. Some aeoniums grow in subalpine regions of the Canary Islands, where temperatures do fall below zero and they cope with some degree of frost, so we have started experimenting with these species to keep them outside all year.

On the cliff face adjacent to the steps leading down to the west end of the walled garden we have planted out Aeonium simsii, A. smithii, A. aurea and A. spathulatum to see how they will survive in this relatively mild section of the garden. Just through the gate into the walled garden, the shade-tolerant A. cuneatum grows under the shrubs in this area. This species is naturally found growing in the laurel forests of Tenerife and it’s already survived one winter here, flourishing in the shelter of the trees and shrubs.

Aeoniums can be seen all year round at Inverewe, particularly in the walled garden. If you visit between the end of May and the beginning of October, you’ll see a splendid display of the National Collection planted out in front of the Gate Lodge at the main entrance.

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