In this section we look at how to grow palm trees in cold parts of New Zealand. We should perhaps clarify that...
How to grow hardy palm trees in places that are considerably cooler than their native environment.
Why do this? Why grow palms in a place that’s colder than where they grow naturally? One answer might be to create a tropical feeling in a cool climate. A very good reason and one we feel sure we can assist you with. There’s a second reason that’s less compelling – to test the limit of what you can grow in your location. We say less compelling because the truth is that in doing this you may test the limits but you’ll likely have a garden full of half-healthy palms that are ‘hanging in there’ rather than thriving.
So think carefully before you begin – are you trying to create a particular garden style or simply be the first to get a particular palm to survive in your climate. Having done both in our London garden we learnt the hard way that the former is great fun whilst the latter is a recipe for disappointment.
At this point we’re going to assume that you’ve a plan in mind but want to find the right frost hardy palm trees to support your vision. There are three things you need to consider:
1. Just how cold does it get in your garden?
2. What cold hardy palms will survive?
3. How you can protect these palms to maximise their chances of success (not merely ‘survival’)
How cold does it get in your garden? We say ‘your garden’ since it’s entirely possible that there may be considerable variation between the temperature as recorded at the local weather station and that in your garden. Our advice would be to compare readings in your garden taken on a chilly night using a maximum-minimum thermometer with that recorded at your local weather station. If you’ve lived in the area for a few years you’ll probably have a good idea about whether you’re in a particularly warm or cool location relative to official records.
Next you want to check the historical weather records for your location. What can you expect in a typical winter? What about a one-in-twenty-years cold snap? Be a little pessimistic. Just before we planted our garden in London we’d had a series of very warm summers and mild winters going back to the 1990’s. Unfortunately, around the time we planted out the first palm trees this marked a change in weather patterns and we suffered a number of cool summers and bitterly cold winters. In hindsight this was probably predictable but we were far too optimistic at the time (in my defence I recall seeing Kentia palms happily growing outdoors in Central London in my first winter there).
Think carefully not just about the lowest temperature you are likely to receive but how long it’ll last. Will temperatures recover within a few hours or is it possible for freezing conditions to remain for a day or more? Similarly, many experts point out that frost in a moist climate may cause more damage than temperatures below zero where humidity is low. Snow too is an important consideration. For many palm trees snow sitting on the leaves can cause damage whilst for others used to such conditions it may protect them from the worst of the cold and wind. Remember also that wind can be one of the most important factors in keeping plants healthy over winter. For many species in the northern parts of New Zealand it’s not so much the cold as sustained chilly winds that cause the most damage. Finally, consider also your summer temperatures. Not only will the palm need to survive the coldest winters but it’ll need to put on good growth over summer. Thus it’s likely that the best plants for the mild but damp West Coast of the South Island will differ from those suitable for Canterbury’s more extreme weather.
Having gained an understanding of the weather conditions in your area it’s time to examine which hardy palm species are right for you. We’ve a handy summary of some hardy species. You probably also wish to consider other hardy companion plants. When deciding which palms to select consider not just hardiness to the cold but also their ability to grow in cool climates and quickly recover from any damage. You also want to be realistic. There’s no point slowly killing a palm tree that’s too tropical for your climate when you could grow something suitable and truly magnificent instead.
In terms of selecting hardy palms remember that large, healthy and mature specimens will be tougher and handle the cold better than small plants. That’s going to add considerably to the cost but there’s little point in planting out a skinny greenhouse grown palm that’ll be dead come August.
Assuming you’re planting one or more palms which are a little marginal in your area you’re going to need to think about protection from the elements. For starters consider your garden’s microclimate. Which direction does it face? Is there a particularly warm spot on the north side of a wall? Or a frost pocket at the bottom of a sloping garden? What is the drainage like? Will you need to build up the ground so that your plants aren’t standing in cold, wet soil all winter?
Next consider natural protection. Think about planting wind protection and an overhead canopy of evergreen plants which can make the difference of several degrees. I’ve seen small palms in sheltered spots (often protected by large stands of bamboo) in London come through winter completely unmarked whilst hardier palms in open gardens are badly burnt by the same frost.
A brick wall or large rocks can also provide a microclimate as the warmth absorbed from any winter sunlight (more likely on clear days prior to a frost) is radiated out at night. Similarly, a position that receives the morning sun will warm faster than a dark south-facing corner.
Another consideration is fertiliser. Some authorities will advise using a fertiliser that’s lower in nitrogen in autumn to avoid encouraging new growth that’s likely to be damaged by frost.
Finally, gently acclimatise your palm trees to your local climate. Avoid buying greenhouse grown palms and if you live in a particularly cold part of the country then plant in late spring to allow the maximum time for the palms to settle in and put on good growth before the cold weather arrives.
You may wish to go further by wrapping less hardy palms with a thick layer of horticultural fleece. This is best purchased as a c.2m roll. First tie up all the fronds and then proceed to wrap the palm 4-5 times tying firmly. The result should be a cylinder that snugly protects the palm. Since the palm won’t be growing over winter you’re safe to keep it dark for several months.
If you want to further increase your chances of success then having tied up the fronds pass a length of soil warming cable through the centre of the bundle before wrapping. Using a long cable one may heat several palms. Some cautions however:
Since the cable will become warm avoid allowing it to overlap or become coiled up.
Use a thermostat. We used this approach in our London garden and even when set at zero we’d occasionally find light burns on the leaves of some palms. Certainly avoid using except when absolutely essential.
Warm cables attract curious animals on cold nights. Cut cheap plastic hosing lengthways and encase the cable inside it. You may wish to cover this or simply scatter cayenne pepper liberally around the area every few weeks. It’s completely harmless to birds and any half-sensible animal will keep well clear.
Finally – and most importantly – always use an RCD and check any wiring with an electrician.