Over Wintering - Ok so you have now grown some of these hardy or semi hardy exotics, what do you need to do for winter protection and keep them until the following year? The answer is that there are many ways, just choose what is appropriate for you and your plant. This could be your Conservatory, Greenhouse, frost free Garage or Shed or some method of Outdoor Protection.
Eucalyptus First of all we can leave these to fend for themselves provided they are given some sheltered position in pots during the first winter. Perhaps against a wall or in a cold greenhouse they should then be ready for planting the following spring.
General All of the other plants with the exception of the Ricinus would be happy over wintered in a frost free Conservatory or Greenhouse. Small plants of even the super hardy Trachycarpus would benefit from this in terms of maximising growth potential. Remember though to keep the plants on the dry side while temperatures are low - over watering them will probably kill them!
Bananas For the Musa Ensete, Basjoo and Sikimmensis, these can be dug up and kept almost dry in a frost free shed or garage and brought back into growth from the corms and rootstock the following year. This is particularly useful for Musa Ensete.
For Basjoo and Sikimmensis these can be also kept alive by cutting off all of the leaves as frosts draw in and wrapping the trunk and base with a protective material like Hessian or horticultural fleece. Bubble wrap will not work as the plant cannot breathe and encourages damp and mildew leading to rot. A good layer of bracken or similar breathable material like horticultural fleece over the rootstock should enable these bananas to withstand 10 or 15 degrees of frost through this method. I have also learnt that it is essential to make sure that the banana is planted deep enough to cover the clumping rootstock below ground.
The alternative is to cut of the plant higher up before frost damage and place chimney liner pots over the top creating a tower around the plant that can be filled with straw. The top covered over to prevent water getting in but allowing air to circulate. This way you may be able to preserve the main trunk and have an even larger plant next year.
Palms - To grow a Washingtonia in a permanent position in the UK is not realistic unless a favoured position with a maximum frost of minus 5°C can be created. You can try wrapping these and other palms in a warming cable set to come on at say -5°C. The costs are minimal when taking into account the number of actual hours the temperature falls below this during a typical winter and it is all the palm needs to withstand temperature extremes. JungleSeeds does have frost protection cables for sale that are self regulating to maintain a temperature above frost level.
The Cordylines as I have said may need some protection of the crown or even main stem in severe winters, but in any case will re-grow from the stem or base as new suckers. My plants in Oxfordshire invariably become damaged if not protected on the worst frosty nights.
Cannas can be dug up place in a pot and put in a frost free outhouse, garage or under the greenhouse bench. Allow the plants to die back on their own. If the pots are then brought into warmth in February they will grow new strong shoots from the rhizome base.
The best solution though is to bring most of these plants into a cold conservatory for the winter, not only are they attractive during the winter but make superb plants the following year benefiting from earlier growth in their protected environment. Please remember not to water them hardly at all in winter if in a cold environment as the damp will rot plants much easier than lack of water.
Brugmansias can be dug up placed in a pot and put in a frost free outhouse, garage or preferably a heated conservatory. Prune the branches by about 1/2 to 1/3rd to keep in shape. You can prune harder but this will delay flowering the following year. If kept cold then only water sparingly but if the plant continues to grow and flourish in warmer conditions water as required.
In milder areas Brugmansias may last the winter outside with growth cut back to the heavier wood or even the root stock, but in our experience this is not an option if the temperatures go below -5°C.