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Caring for Chocolate Trees

Chocolate trees (theobroma cacao) aren't naturally suited to the UK, but with some care and attention (or a shaded, humidity-controlled greenhouse), they can be nurtured and toughened up to some degree as indoor pot plants, provided that you're aware that potential disaster is always hiding around the corner, and provided that you realise that if the plant survives, its going to want to become a tree. If you can recreate the conditions of a semishaded rainforest canopy region, a plant should be happy.

There's a successful, decent-sized chocolate tree available for viewing in the Palm House at Kew Gardens, but it's in the tropical greenhouse area, with spritzers constantly misting the air. This isn't something that most of us can do at home.

Growing

Plant the sprouting beans in a compost-sand mix and incubate warm and moist. I used a large transparent 500ml yoghourt pot for initial potting, with a matching clear 500ml pot inverted as a cover, then put several of these into a larger transparent box with water in the bottom, with another matching inverted box as a lid, then put the whole thing into an airing cupboard. This allowed the monitoring of shoot and root growth and watching for possible fungal infections without creating a sudden temperature drop when the cupboard door was opened. Once the seedlings were two or thee inches high, they were moved to a larger incubator, with small fluorescent strip lights providing light and limited heating, again with a double- wall, and with a little water in the outer box for humidity.

After they reached a foot in height, I started to acclimatise them to room conditions (at which point further growth slowed dramatically).

Growth is intermittent and sporadic, and happens in spurts. This probably gives the plant additional protection against pests that target fresh growth, but makes it more difficult to assess the affect of different environments and treatments.

Maintenance

The owner of an "indoor" chocolate tree owner has to be mindful of three main dangers:

excessively dry air will kill them - the paper-thin leaves will quickly dehydrate and die
excessive heat and/or light will kill them - the thin leaves will dehydrate and die
cold will kill them - the leaves will fall off, leaving you with an unattractive dead-looking brown stick.

Resist the temptation to put a potted chocolate tree outside in full sun on a summer day to let it get a bit of air. One day of strong summer sunlight = full leaf-drop. While the resulting "stick" can theoretically be coaxed to start sprouting again, this can require an intensive-care "bubble" and several months of attention, and really, if this happens, you're probably better off starting again from scratch. If you are growing these plants from seed, plant twice as many as you want: accidents are inevitable, and if you are building an incubator , it might as well be housing a whole batch of seedlings rather than just one or two.

The plants can get to a couple of feet high before they start branching, which makes for a more boring house-plant (especially as the lower leaves drop). To get a more bushy and interesting shape (that's looks less like a stick with leaves on), you can deliberately damage the very tip of the plant (once it's established) to encourage adjacent tissue to bud out into multiple branching stems, although doing this to a "precious" plant requires a certain amount of nerve.

Vacuum cleaner alert:

The natural enemy of the indoor chocolate tree is the vacuum cleaner. An established indoor chocolate tree may accumulate some dust on its large dark-green leaves, and when someone is having a bit of a hoover about, they see the dust and instinctively lift the vacuum cleaner nozzle to somewhere near the plant ... at which point the entire plant tries to hurl itself bodily into the vacuum cleaner, Kamikazi-style. Those big paper-thin leaves and bendy green stems mean that a split second after wafting your cleaner past the plant, you're hearing the "thobboowwwooth" noise of a chocolate tree rattling about inside a vacuum cleaner. It has to be seen to be believed. Brief everyone in your household about your tree's dangerous affinity for vacuum cleaners. Chances are they still won't believe you until it happens to them.

Heat and light

You may be able to get away with putting your tree on a window shelf near a radiator (which may stop it getting a chill), as long as the updraft doesn't play over the leaves. The best solution if the tree is in a waterproof pot, and really has to be near a radiator, is to place the pot in a large, deep, wide bowl and keep this bowl topped up with water, and to use jutting placemats to deflect any rogue updrafts. The water will give the plant's roots additional temperature stability, will increase humidity on those dangerous hot days, and will help to humidify any radiator updrafts as they play over the bowl and pass over the surface of the water.

Even through window-glass, one day of strong UK summer sunlight can be enough to badly damage a plant, so listen out for "UV" alerts and sunblock warnings on the weather forecast. Spritz your plant once or twice a day during sunny weather, and consider also spritzing the inside of the window glass: this is an excellent way of providing local humidity, and also scattering strong sunlight. Wrapping a waterproof pot's exterior in paper allows water from the bowl to rise up by capillary action and then evaporate, helping local humidity.

The ideal room for a chocolate tree would probably be a warm shower-room with strong sunlight, which will already be scattered by the room's frosted window-glass (so no light-scorching), in constant use (so high humidity).

Cold

There are accounts of people's beloved chocolate trees dropping dead when someone has left a greehouse door open for a few hours in cold weather. Avoid.

Pest control

The woody leaves make chocolate trees unappetising to most creatures, but when kept indoors, wooly aphids may attack the soft crowns and leaves. The accelerated growth-spurt that he leaves go through means that a bite to a leaf when small from a wooly aphid can translate into a large hole, blemish or tear when fully sized. standard counter-measures for wooly aphids can be used: pick them off the plant with a bamboo skewer, and spray with a solution of organic washing up liquid.

Disease control

Fungus is liable to be a problem in any situation where a plant is kept in a warm, extreme-humidity environment (such as when germinating tropical seeds or incubating seedlings). Warm, moist compost encourages fungus, and happy fungus will then attack plants. A quick dusting or spraying with Bordeaux mixture should fix this. You're liable to encounter these problems when trying to grow or incubate other tropical plants in warm, moist conditions, so it's a good idea to source some Bordaux mixture (or a substitute) before you start.