Many people imagine that you need a heated glass house to grow tropical plants here in the UK. Interestingly, however, you can grow a range of tropical plants even in our cool temperate climate. Some can be grown outside, and are surprisingly hardy, while others can be grown in a heated polytunnel or double polytunnel which can provide the extra heat required – especially when extra lighting is also provided to combat the short growing season.
Why Grow Tropical Plants?
It may seem ludicrous to try to grow plants suited to the tropics in our climate. But if you want to stretch your gardening muscles, and increase the range of crops and ornamental plants that you are able to grow, tropical plants could pose an interesting challenge.
Usually, it is best to devote most of your garden to plants that are well-suited to the climate and conditions – the right plants for the right places. But on occasion, growing tropical plants can be an interesting objective for more experienced gardeners.
Which Tropical Plants Could You Consider?
When looking at which tropical plants to consider, the first thing to think about is, of course, whether you will plan to grow your plants outdoors, in a regular polytunnel, or under even more protection (such as a double polytunnel). The more protection you provide, and the closer to a tropical environment your growing areas can become, to wider the range of tropical crops that you will be able to grow.
Growing Tropical Plants Outdoors
First of all, let’s take a look at some of the best tropical plants that can be grown outdoors in a UK climate:
- Chusan palm (Trachycarpus fortunei)
- Dwarf fan palm (Chamaerops humilis)
- Cordyline Australis
- Bean tree (Catalpa ‘Bungei’)
- Bamboo (Phyllostachys nigra etc.)
- Male fern (Dryopteris filix-mas)
- Dragon arum (Dracunculus vulgaris)
- Elephant Ears (Colocasia)
- Phormium (various varieties)
- Ginger Lily (Hedychium aurantiacum)
- Arum lilies (Zantedeschia aethiopica)
- Starfish lilies (Ferraria crispa)
- Fatsia (Fatsia japonica)
- Bamboo iris (Iris confusa)
- Passion flower (Passiflora)
- Bird of Paradise flower (Strelitzia)
- Horse tails (Equisetum arvense)
- Bear’s breeches (Acanthus mollis)
- Trillium (Trillium grandiflorum)
- Rogersia (Rogersia pinnata ‘Superba’)
- White Egret Orchid (Habenaria radiata)
- Coral Drops (Bessera elegans)
Of course, like any plants, tropical plants differ in their requirements. Some of the above will require moisture, while others like it dry. Certain ones will do best in shade, while others will require full sun. Some are tender summer plants, while others do have a degree of hardiness and can stay in the garden year round (sometimes with just a little protection for the tips). It is important to carefully research the requirements of each and every tropical plant you are considering to make sure that you are able to meet their needs in your garden.
Growing Tropical Plants In A Polytunnel
Owning a polytunnel can make it easier for you to grow a wider range of tropical crops, and to grow tender or semi-hardy plants without having to move them indoors or undercover during the winter. If you take steps to heat your polytunnel over the winter months, it is possible to create a climate inside that is much warmer than that experienced elsewhere in your garden.
Tropical Crops in a Single Polytunnel
If you want to grow edible tropical crops, a single polytunnel can be sufficient for a wide range of options. Even an unheated tunnel can extend the growing season and make it easier/ possible to grow a range of crops that usually require too long a season to grow in the UK. For example, it would allow you to grow:
- a range of different beans commonly grown in the tropics,
- squashes, melons and other curcurbits,
- sweet potatoes,
- ginger, and potentially, provided the right conditions are provided:
- tropical root crops like taro, and cassava
- vanillaand more…
Creating a Double Polytunnel
Certain tropical plants will need more protection from the cold, and are usually grown under glass. However, some gardeners in the UK have also succeeded in growing such plants within a double polytunnel structure. The light levels within a double polytunnel will, of course, be lower. But the added insulation can make it much easier to effectively heat the space in winter, and so could increase even further the range of plants which it is possible for you to grow.
For example,using a double polytunnel structure, gardeners have even managed to grow and get a worthwhile yield from banana trees right here in the UK!
Making a double polytunnel is simply a case of erecting one polytunnel inside another, trapping some air between the two layers of plastic to reduce heat loss from the structure.
Heating a Double Polytunnel
Heating a double polytunnel to create a tropical environment within can be accomplished in various different ways. You can first help to regulate temperature and maintain a more stable environment by introducing more thermal mass into the structure.
You can also increase temperature through composting materials in ‘hot beds’, in which decomposing organic matter warms the soil in your growing areas from beneath.
Beds can also be warmed by using heat transfer pipes from below ground, or you could also consider running hot water pipes through the structure. (These can be powered from renewable energy such as solar panels, for a more sustainable solution.)
Air temperature can be raised to tropical temperatures (25 degrees or so) through the use of electric heaters. For sustainability, these too could be run from renewable power generated on site. (This would also significantly reduce the cost of tropical growing here in the UK.
Tropical Fruit Trees To Grow in Containers
If you enjoy tropical fruits, a heated polytunnel could provide you with a place to put tropical fruit trees that you are growing in containers. With better ventilation, and easier humidity control, a polytunnel could be a better place to keep such plants than indoors, inside your home.
In addition to growing warm climate fruit trees such as:
- citrus trees
- pomegranates etc..
In a double/ heated polytunnel you could also potentially grow tropical fruits such as:
- and even bananas!
Creating a Polytunnel Banana Plantation
It is possible, in a heated,humidity controlled double polytunnel, to create conditions that strongly resemble those in a tropical country. That means that you can grow bananas and other tropical crops in much the same way that they could be grown in those countries.
One fantastic way in which bananas are grown in the tropics is in a sustainable, eco-friendly system known as a ‘banana circle’. (This system can also be used to grow other fruiting trees and companion plants.)
UK gardeners might consider creating a banana circle in a large double polytunnel, though dwarfing or semi-dwarfing banana trees will make it easier within the space available.
In this layout, circles of around 2m diameter are created.
- A hole or pit is made inside this circle, and filled with food waste and other organic matter to feed the trees.
- Banana trees (alongside other trees if you wish) and planted on a raised ring (around 60cm wide) around this pit. (Seven trees per circle.)
- Companion plants are then placed around the circle between the banana trees.
Companion plants include cassava and taro, lemongrass, citronella, sweet potato, watermelons, pumpkins or squash. Beans can be planted to fix nitrogen and climb up the banana trees.
Creating tropical habitats right here in the UK can help us to learn about sustainable food growing systems that could be of benefit in tropical countries, as well as allowing us to grow foods that are common in supermarkets, but which cannot usually be grown here. Growing these foods here can reduce our carbon footprints and reduce food miles, and so is kind to our planet.
While, of course, most of us will stick to plants better suited to our climate – a few intrepid gardeners can break down barriers and try something new – creating a taste of the tropics right here in the UK.
Do you grow any tropical plants in your garden? Please feel free to share any hints or tips you may have in the comments below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.