Tropical Nursery blog
The Tropical Nursery at Kew provides a home to the permanent tropical and temperate collections. It comprises 21 different climate zones and holds an estimated 35,000 plants.
The nursery is split into four teams that each have a specialism; orchids, moist tropical, cacti and succulents and temperate and island flora. The Tropical Nursery is normally off limits to the public so this blog provides a peek into the fascinating world of the largest nursery at Kew, and the work of the staff there.
A touch of the exotic
As the last colours fall from the trees under our grey skies, and we brace ourselves for the winter ahead, a touch of exotica is required to escape the gloom. Here in the Tropical Nursery at Kew, a whole array of far-flung wonders of the plant kingdom are cared for, and nothing suggests the spirit of the exotic like the flowers of the mallow family, known botanically as Malvaceae.
The Malvaceae family
Found in temperate and tropical regions of the world, these delightful plants can be easily recognised by their often brightly-coloured, funnel-shaped flowers, with 5 separate petals and distinctive protruding stamens surrounding the pistil.
A widely grown member of the mallow family is the hollyhock, often found leaping waywardly from flowerbeds in the height of summer, but here in the Tropical Nursery we have the riches of warmth all year round to grow some of the 3,700 species of Malvaceae that occur worldwide.
Phymosia umbellata from Mexico growing in the temperate zone of the Tropical Nursery
Seen here are the stunning scarlet flowers of Malviscus arboreus. Known as the sleeping hibiscus due to the petals remaining closed, this adaptation allows the flowers to be pollinated only by hummingbirds and butterflies that are able to hover as they feed, unlike other pollinators that require a landing pad. They move from one plant to the next, drawn in by flashes of red amongst the canopy. This sleepy adaptation encourages more precise and successful pollination.
Found growing in subtropical areas of southern Texas and Florida, as well as the cloud forests of Mexico and Colombia, this plant will be one of the floral delights in Kew’s Temperate House when it opens once again.
Malviscus arboreus in the temperate zone of the Tropical Nursery
Many plants of the mallow family are grown in the temperate zones of the Tropical Nursery, some finding a home here while the Temperate House is restored to its former glory, and some on a more permanent basis due to being endangered or even extinct in the wild.
The elegant white petals and musky purple stamens of Trochetiopsis ebenus are a joy to see right now, but for over a century this member of the mallow family was thought to be extinct.
Endemic to the remote island of St Helena in the Atlantic Ocean, this glorious shrub had a close shave with vanishing from those distant shores forever. Sailors and explores would draw up on St Helena to rest their sea legs, leaving goats on the island to feast upon their return. Having not evolved to withstand the constant nibbling of these rotten goats, the vast hillsides of Trochetiopsis ebenus were diminished, and by the mid-19th century were thought to be extinct.
However, by sheer determination, two plants were found clinging on a cliff face in the 1980s. Heroic efforts were made by a local to collect cuttings, which were then sent back to the UK and grown on in botanic gardens including Kew. Kew is now involved with efforts to re-introduce this valiant species back to its rightful place.
Trochetiopsis ebenus in the temperate zone of the Tropical Nursery
Hibiscadelphus is a genus in the mallow family endemic to the land of all tropical dreams, Hawaii. The flowers of this genus are of a curious nature. Hiding beneath lush green leaves their subtly coloured petals remain wrapped up while the stamen and pistil explode outwardly. Of the seven species described, four are now thought to be extinct. A further two more are extinct in the wild but persist in cultivation, one of those being H.hualalaiensis, seen below.
The only species known to still have wild populations is H. distans, with around 20 wild trees and 150 re-introduced specimens. The serious decline of this genus is thought to have coincided with the arrival of the Polynesian rat (feeds upon seeds) that came with early Hawaiian settlers.
Hibiscadelphus distans (left) and Hibiscadelphus hualalaiensis (right) growing in the temperate zone of the Tropical Nursery.
Where to see them
While some of these temperate mallows reside here in the nursery during the Temperate House restoration, many can still be found growing in the Princess of Wales Conservatory at Kew, as can many of their tropical relations. Failing that, go and buy yourself a pack of hollyhock seeds today to grow your own exotic blooms for next year!
- Jack -
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Inside the Tropical Nursery
As a glasshouse trainee at Kew Gardens, I get to spend six months working inside the Tropical Nursery, the biggest area of glass within the whole grounds. It covers 6,500 m² and we cultivate 46,000 plants inside the 21 climate controlled zones. They are grown not only for display in the great glasshouses of Kew, but also for scientific research and conservation work carried out here and at Wakehurst Place.
I work in the Tropical Nursery’s arid section, which is made up of a ‘tropical warm arid’ zone as well as two ‘cool arid’ zones. Here we cultivate plants especially adapted to life in the arid regions of the world, such as those in the Cactaceae, Aizoaceae, Geraniaceae and Euphorbiaceae families, as well many others. As a trainee, I am continually learning through hands-on experience looking after the living collections. I work closely with staff, volunteers, interns, students and my manager Paul Rees, who teaches me and encourages me to ask questions.
Paul and I talking about plants at the Tropical Nursery Open Day
One of my favourite jobs is creating displays for the Princess of Wales Conservatory. Each Friday, as a team, we choose plants that are of notable visual interest that week, or are significant because of their conservation status.
Many of our plants share similar habits or adaptations and we are able to use the displays to communicate and illustrate these to the public. A few weeks ago we developed a theme on ‘summer dormancy’, showing how plants such as various Tylecodon and Conophytum burst back into life at this time of year and the various stages of their growth and re-emergence. We entitled the display ‘Sleeping Beauties’ and, alongside the plants we presented information, written by Paul, explaining the processes and why they occur.
Our ‘Sleeping Beauties’ display
More recently, we assembled a display of Madagascan plants, positioning spiny succulents close together in order to simulate a dense and spiky desert jungle. Paul was keen to highlight the biodiversity crisis this unique environment currently faces, so we presented information that highlighted the threats, as well as the hope offered by the research and conservation team that Kew coordinates both in Madagascar and the UK. We also wanted to attract the attention of younger visitors, so diploma student David Richter set up toy lemurs among the plants, an instant draw for our younger visitors.
Children looking at our ‘Madagascan’ display
It is also important that the displays have great visual impact, so Lorraine Barker, who has a wealth of experience designing and creating horticultural displays, leads our group with the positioning of the plants, creating balance, symmetry and contrast.
Janaka Balasuriya, Lorraine Barker, Paul Rees and David Richter prepare the plants to be put out on display.
Our current display project is entitled ‘Solution to a Prickly Problem’ and focuses on the adaptations for pollination in some of our cacti. We wanted to show and explain how some plants evolved to protect themselves from predators while simultaneously protecting pollinators, such as birds, that visit their flowers. For example, Melocactus produce a soft red cushion, called a cephalium, on top of the stem which prevents pollinators from being harmed by the cacti’s own sharp spines as they feed from the flowers.
We also wanted to explain how staff such as Noelia Alvarez are collecting seed for the Millennium Seed Bank, based at Wakehurst Place. They hand pollinate flowers and then cover them with a very fine mesh bag to prevent any inadvertent pollination taking place via insects, as Noelia explained in her recent blog post on the subject.
Our ‘Solution to a prickly problem’ display with mesh bags on Melocactus
While not only being interesting to visitors, we feel that by communicating what is special about our plants or why they happen to be endangered, we contribute towards the conservation of them in their natural habitats. There is much work done behind the scenes at Kew Gardens and Wakehurst Place, and displays such as these enable us to give the public further insight as to what is going on. The succulent displays can be found in the arid section of the Princess of Wales Conservatory.
- Miranda -
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The Great Glass Houses and Tropical Nursery at Kew are home to some world-famous edible plants. You might see familiar fruits such as bananas and papayas, or find your daily caffeine boost in its natural, unprocessed state – as dark coffee beans or the leaves of the tea plant, Camellia sinensis. But not many people know that Kew is also home to the oldest cultivated crop in the world. It is a member of the Araceae family, otherwise known as aroids - a diverse group whose edible species include one that gives ice-cream its vanilla flavour (despite being named after a cheese), and the intriguingly named 'fruit of the devil'.
The oldest aroid
The oldest cultivated crop in the family is Colocasia esculenta, commonly known as taro.
Taro (Colocasia esculenta) in Kew's Princess of Wales Conservatory
It originated in tropical Asia and has been cultivated for more than 10,000 years. Today, taro is naturalised throughout the humid tropics and subtropics, and around 400 million people include it in their diet. With the crop from one square kilometre capable of feeding 5,000 people for a year, its long-term popularity comes as no surprise. The tubers are a good source of carbohydrate (13-29% of the cooked weight depending on cultivar) and are richer in protein than most other major starch crops. The leaves of certain cultivars are eaten like spinach and are an excellent source of vitamin A, vitamin C and minerals. The tubers can be ground into a flour to make bread and other bakery products, or sliced and fried to make crisps. Like most aroids, though, the presence of toxins means that all parts must be cooked to render them edible, and in general they are boiled or roasted. Taro’s natural habitat is tropical humid forest and in the tropical nursery at Kew it is grown in humus-rich compost at around 22°C and 70% humidity. As it often grows along stream and pond edges, taro does tend to be rather thirsty.
The second most important edible aroid is the genus Xanthosoma, commonly known as tannia or cocoyam, and again both the tubers and leaves are eaten.
Tannia (Xanthosoma sagittifolium). Note the purple stems
Widely cultivated in tropical America since pre-Columbian times, Xanthosoma spread to Africa and Asia and is still in the course of migration. X. caracu is now commonly grown in Florida in response to the growing population of immigrants from the Caribbean. The main cultivated species is X. sagittifolium, which can be seen in the Palm House showing its striking purple stems and purple veins beneath large, light green leaves.
A giant aroid
Where Colocasia might reach one metre and Xanthosoma two metres in height, Alocasia macrorrhizos, commonly known as giant taro, can grow up to four metres tall and have leaves one metre long.
Giant taro (Alocasia macrorrhizos)
This giant aroid can be seen in the Princess of Wales Conservatory. Its corms are coarse and acrid and generally it is the thick, starch-filled stems that are eaten. In Malaysia it is used in ‘curry santan’; it is first soaked in water with betel nut chips or slaked lime to remove the acridity, and then boiled in coconut cream with spices and dried prawns. When correctly prepared and cooked the stem also yields white flour.
Other giant aroids can be found in the Amorphophallus genus. A. paeoniifolius - common name the elephant yam - has tubers that can reach 25 kg in weight. It is cultivated in tropical Asia and India and is an important standby if the rice crop fails. Yielding slightly smaller tubers is A. konjac, the konjac plant, which weighs in at a mere 10 kg. This species has been cultivated in China for 2,000 years and is used to make a variety of food products. It is used not only as a root vegetable, but also to make 'konnyaku' (a gelatinous ingredient in many Japanese foods), flour (from which noodles and cakes are prepared) and jellies. The tubers are also the commercial source of mannose, a substance used in diabetic foods. These impressive plants appear treelike but are in fact composed of just one leaf. They are also seasonally dormant and so may be hard to spot in the public glasshouses but, should you visit on a tropical nursery open day, an array of Amorphophallus may be seen in zone 8.
The swamp aroid
There is even an edible aroid that grows where nothing else will – in stagnant, brackish swamps. Cyrtosperma merkusii, the swamp taro, is cultivated in Southeast Asia and the Pacific. It needs the longest growing time of all the edible aroid root crops, on average requiring 3-6 years before harvesting, but goes unchallenged by quicker growing crops as they won’t tolerate swampy conditions. On coral atolls in the Pacific it was successfully grown by being lowered in compost-filled baskets into pits, often more than one metre deep, dug through the coral limestone or sand to the water table. As easier, imported foods have become available in the region many pits are now unused.
The Swiss cheese plant (Monstera deliciosa)
Monstera deliciosa, named the Swiss cheese plant because of the holes in its leaves, is actually used to flavour ice cream. It is cultivated in Mexico and Central America and the flowers and fruits only appear once the plant has reached maturity - at around 22 metres in height with leaves up to 90 cm long and 75 cm wide. The fruits are protected by an irritant outer layer, but when the berries are ripe the protective cover breaks away. They have the scent and taste of pineapple and banana combined.
The 'fruit of the devil'
And the 'fruit of the devil'? This is Montrichardia arborescens, cultivated in South America for its starchy tubers, and acquired its nickname due to its irresistible fruiting spadices which produce large infructescences, each containing about 80 edible yellow fruits. At Kew we're growing a juvenile specimen in our Tropical Nursery.
Kew's Montrichardia arborescens in the Tropical Nursery. Note the tree-like stems which give the plant its Latin name. We're hoping this specimen will fruit later this year. (Image: Simon Port, RBG Kew)
Aroids have long been a food staple to many populations and even though lifestyles across the world may be changing there’s still plenty of potential for their use. As just this small selection has shown, aroids can provide high yielding nutritious crops, substances for specialist diets and gels for the food industry. With further research and development other beneficial applications may well be discovered. Perhaps one day we Brits may even find the 'fruit of the devil' turning up in our local greengrocers!
- Louisa -
Tags: useful plants
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That time of year is upon us again... it’s Kew’s Tropical Extravaganza! This year’s festival is inspired by the forces of nature – earth, fire, air and water - and I was thrilled to be given the opportunity to help transform the Princess of Wales Conservatory into an explosion of colour in celebration of the elements.
Orchids really are the stars of the show and this year’s selection won’t disappoint. Bright yellow Oncidiums and vibrant Phalaenopsis decorate the pillars, stunning blue Vandas form a tropical arch and elegant Dendrobiums festoon the giant hanging baskets.
Volunteers behind-the-scenes working on the plants for the displays
Decorating the pillars
My first task of the week, and one of the largest, was to help decorate the pillars. Behind the scenes, an army of volunteers prepared each pot for mounting. They drilled two holes in the back of the pot, through which a wire hook was inserted, and then they attached a wad of moss to the front of the pot with a rubber band to camouflage the container in the display. After watering, the pots were passed to those of us perched at the top of a ladder where we could begin to fix them to the pillar. Each pillar was already wrapped in coir and covered with a strong plastic mesh to which we attached the pots using a cable tie through the mesh and the wire hook of the pot. The cable tie was tightened to hold the pot in position and we worked down the pillar attaching each individual plant in much the same way as a patchwork quilt is assembled.
The team dress the pillars from ladders and reach the top of the tallest pillar from the cherry picker
In at the deep end
The large ‘twister’ in the lily pond was designed to give visitors a sense of the movement of air and wind, the element used by many plants to disperse their seeds. Blood red Begonias and Guzmanias, yellow Anthuriums and orange Kalanchoes were mixed with silver foliage plants such as Tillandsia usneoides to represent air and cool wind. I donned a pair of (leaky) waders, filled a floating wheelbarrow with plants and compost and lowered myself into the pond. This was a fun job! I love planting up any kind of display but doing it waist deep in water just made it cooler. The plants are only going to be in this display for the short term (the duration of the festival) and won’t have much time to grow and fill out a large space, so we planted them unusually close together. The result – a display that looks full and appears well established. Stunning!
Working on the ‘Twister’ display in the lily pond
Every year I marvel at the finished product and I’m really happy that this year I got to participate. It was busy, physical, hot, challenging - and one of the most memorable and fun weeks I have spent in this job. I can’t wait to take my friends and family around the festival to point out all our hard work! I’m sure they will appreciate it, just as I did when I could only guess at the imagination that went in to it.
- Kirsty -
Find out more...
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The titan arum is not the sort of plant you can be neutral about. It is curious, weird, rather obscene, revolting and even terrifying. Scientifically known as Amorphophallus titanum, it is by no means easy to tell that it belongs to the Araceae family, which includes the ‘Swiss Cheese Plant’ (Monstera deliciosa) with its unmistakeable foliage, the virginal ‘White Arum’ or ‘Calla Lilly’ (Zantedeschia aethiopica), the ‘Flamingo Flower’ (Anthurium andraeanum), and the ‘European Arum’ or ‘Lords-and-Ladies’ (Arum maculatum and A. italicum).
The flower of Amorphophallus titanum is indeed very odd. It consists of a single bract (modified leaf) called a spathe, which provides cover for a central flower-bearing protuberance, the spadix. This floral peculiarity is technically an inflorescence, not a flower; the real flowers being tiny and protected at the base of the spathe. The shape of this inflorescence has inescapable sexual connotations beyond the fact that it is the plant’s reproductive apparatus.
Inflorescence of the titan arum
How we grow them at Kew
The titan arum is a tuberous species that characteristically has dormant periods when leaves are not present, and these normally correspond to the dry season (or winter) in the habitats where it grows. At Kew, we grow them in huge containers that hold tubers which can reach up to 90 kg. The leaf is a marvel in itself and at first glance resembles a sapling tree. It is patterned with irregular pale green blotches, which at a distance render it indistinguishable from the moss and lichen encrusted on the trunks of surrounding trees. At the apex it divides into three, and then again into several more divisions, making an umbrella of leaflets about 7 m in diameter.
Titan arum in the Tropical Nursery at Kew
In the Tropical Nursery at Kew, Amorphophallus titanum is not very difficult to grow, provided a number of conditions are met. These are roughly: a rich soil and trace elements, the use of additional fertiliser, shading against direct sunlight, a minimum temperature of 22⁰C during the day and 19⁰C during the night, a well defined resting period, and strict control of pests.
The plant must be kept in a well drained soil. If the soil becomes too dense (because of excess water or too much loam) the roots will rot. The health of a tuber is finally measured by its increase in size, and a tuber that is doing well may triple its weight in a single season.
Charles Shelton (on the left) and Marcelo Sellaro weighing the titan arum tuber
In cultivation at Kew, A. titanum shows a strong tendency to take dormant periods, usually twice during the growth cycle. When a leaf dies down after a regular growing season, the tuber will invariably take a rest period. Following this another leaf may emerge. When the plant is mature enough to flower, the resting period is usually considerably shorter and may take no longer than a month, or sometimes even less.
Rare flowerings of the titan arum
Pollination of different clones in cultivation rarely occurs. In 2009 two specimens flowered at Kew. This allowed cross-pollination using both fresh and frozen pollen grains, which were put on the stigmas on the first day of flowering. When the female flowers are receptive, the stigmas are very sticky and ready to receive pollen. The yellow rind of the appendix emits an overpowering, nauseating stench that gives the plant its Indonesian name of ‘bunga bangkai’, meaning “corpse flower”. The smell is perhaps the most powerful and disgusting odour produced by any plant. It was described by Sir Joseph Hooker (1891) as a mixture of rotting fish and burnt sugar, which turns your stomach over and makes your eyes run.
The stalk formed about 100 fresh berries, which turned into orange reddish fruits when ripe. After removal of the pulp the seeds were sown in a mixture of ½ part coir, ½ part sand, and watered daily. Seedlings were established after one month. Any seeds stored dry lose viability very quickly because the seed coat is rather thin and does not protect the embryo from desiccation (drying out).
Any success in propagating A. titanum, by any means, is a triumph of hope over adversity. For almost a century it was considered near impossible, but now the corner has been turned. Not only have viable seeds been produced in cultivation, but young plantlets have also been raised vegetatively by leaf cuttings.
If the features outlined in this text have captured your imagination, I hope that seeing a specimen growing in the Princess of Wales Conservatory will persuade you to explore the world of Aroids further, and serve as a general introduction to this impressive family of plants.
- Marcelo -
Find out more...
- More from Kew about the titan arum (Amorphophallus titanum)
- International Aroid Society
- Fairchild virtual herbarium
- Recommended reading – ‘Aroids: Plants of the Arum Family’ by Deni Brown
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About the Tropical Nursery
The main functions of the Nursery are to:
- Form a back-up collection of tender tropical plants used to support science, display and education within the gardens. We supply plants for use in displays in the Main Kew conservatries, for festivals and events organised by the Foundation and the Directorate.
- Supply plants for education purposes to the Schools & Families department.
- Act as main propagation facility for the Princess of Wales Conservatory, Palm House and Temperate House as well as supporting the exchange of plants between Kew and other institutions and collections.
- Provide direct education in nursery techniques and the cultivation of tropical plants for the Kew Diploma course, Apprentice and Trainee programme, Internship and work experience programmes and visiting staff from other UK and overseas institutions.
- Support conservation by working with the UKOTs team undertaking propagation and cultivation protocols on targeted endangered species.
The beauty or the beast?: Hi Jean-Michel. Thank you for your enquiry. Yes, Amorphophallus titanum usually has large berries (o ... by: Kew feedback team
The beauty or the beast?: Hi I ve planted two seeds of amorphophallus Titan last year, and they are now about 50cm high I v ... by: Jean-Michel Touche
Monstrous deliciousness and devilish fruit - Kew's edible aroids: I have already tried eating M. deliciosa fruit, perhaps taste like pineapple and banana...I have als ... by: Marcelo
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