20 June 2016

Caring for Kew's chocolate trees

Cacao tree is native to South America, and is not easy to grow in Britain. Find out how Kew horticulturist Nick Johnson has been involved in growing specimens at Kew, with three new cacao trees flourishing in the Princess of Wales Conservatory.

By Nick Johnson

Cacao princess of wales conservatory

Six cacao trees at Kew 

Cacao tree (Theobroma cacao), also known as cocoa, cocoa tree and chocolate tree, is a special plant at Kew. 

We currently have six on display in the Palm House and the Princess of Wales Conservatory. 

Most were grown from a single seedling donated to us from a private individual in 1988. It has never been given a variety name but I believe it to be Theobroma cacao ‘Forastero’, which is the higher yielding common cacao in trade. 

Protecting the fruit

When I joined Kew in 2002, this tree grew in the centre section of the Palm House. It was multi-stemmed and fruited occasionally. 

The pods were so precious at the time, we had to put little nets around them as they developed, to prevent the pods being stolen before they were ripe. 

Planting a cutting in the Princess of Wales Conservatory 

A cutting of this tree was planted in the Princess of Wales Conservatory in the late 1990s, because it was felt that the Palm House couldn’t give the tree enough light to fruit well. 

This tree is now a giant, fruits successfully twice a year, and is a favourite of many visitors. 

Unusual flowering methods 

One of the reasons cacao tree is unusual, is because it flowers on old wood. It will flower best on wood that is more than three years old. 

The term used to describe this unusual flowering method (production of flowers from older wood) is cauliflory. In the wild, the tiny flowers borne on the trunk and branches are pollinated by small flies like gnats and possibly mosquitos. 

Each flower usually only lasts a day, and we have found that pollination (which is done by hand here at Kew) is best done early in the morning. 

The trees tend to put on two flushes of flowers per year, one in the spring and another in the autumn, so we usually have fruits on at least one of our specimens all year round. 

Inside the pods 

Inside a cacao pod (which is technically termed as a berry) you will find more than a dozen seeds tightly packed and surrounded by a white, jelly-like, flesh. 

Occasionally, when we have time, we like to cut down a ripe pod, open it up and offer a spoonful of the flesh to passing visitors. The taste is unlike any fruit I have eaten, a kind of cross between passion-fruit with the tangy taste of a mango. 

Challenges of growing cacao trees in the UK 

Growing cacao trees in the UK is not without its challenges. 

The species comes from areas of South America that can experience rainfall of up to six metres a year! This can be hard to replicate in the glasshouses, particularly during winter when high humidity can cause the pods to rot. 

We have to find a good balance between giving the plant what it needs but not necessarily what it wants. The cacao tree is also hungry, requiring good balanced fertiliser applications on a regular basis. 

We are visited regularly by a Columbian cacao farmer, who offers advice and feedback on pruning and plant husbandry - his advice and support is invaluable to us. 

Three more plants in the Princess of Wales Conservatory 

Our big cacao tree in the Princess of Wales Conservatory has done so well that we decided to plant three more of the same variety in that area. Over the coming years, we are hoping these trees will fruit as prolifically as the big one. 

Come and see the cacao tree in the Princess of Wales Conservatory