I find myself these days starting answers to Bonsai related questions mostly with “it depends”. This topic will be the same. Your local climate and setup will largely determine what you do with your Bonsai trees during Winter. As most of the Blog readers will rightfully ask about the purpose of this topic this time of the year, the simple answer is that most of the readers are in the USA and I am in New Zealand / Aotearoa. It is Winter here now.
This could be a good example of how local climate can differ. Parts of the South Island and inland North Island, will have snow on the mountains with below freezing temperatures at times. The same will be true for Northern Hemisphere countries during that Winter. It all depends!
Here is a video from a few years back of some of my Bonsai just as it started to snow.
The main things to look out for are:
- Light needs
As most trees will go dormant or at least slow down with the onset of Winter, it is important to make sure that you adjust to the water requirements that comes with this. The main problem is being too wet. This can lead to root rot. The best way to tackle this is to be pro-active by ensuring that all your trees have a well draining soil mixture and that the pot drainage holes are open. I have found many a spider’s nest and snails blocking the hole partially from the outside. Another technique is to place the pot at an angle for water to run off during periods of heavy or consistent rain. Needless to say is that when you are in a high rainfall area is to switch automatic watering systems off during this time. It is as important to check trees regularly / daily for water requirements. Be especially on the lookout for trees that might be partially protected by trees, fences or roof overhangs. The front row of trees might be wet, but those in a “rain shadow” might be very dry.
Frost is the biggest enemy here. It is reported that for some species snow is not a problem as it could insulate the tree from harsher elements like wind. Wind for me is a major problem. Not only does it dry leaves out, but in Winter it causes a wind chill, sometimes far below areas out of the wind. Trees not accustomed to these very low temperatures must be protected. This will include over-wintering in a basement, garage, shed or at least a conservatory of some sorts. I personally do not have many trees with this requirement, but do have a few sub-tropicals, inclusive of Bougainvillea that needs protection. This is done in the form of just placing it under a bench when frosts are expected or using a cold frame. Trees that you work on during Winter, even if it is just wiring, should be kept in a better climatic area for a few days after the work was done.
It is mentioned in the paragraph above that trees can be over-wintered indoors. As deciduous trees will be without leaves, light requirements do not matter too much, but it is important to take note that plants rely heavily on day and night length differences to keep seasonal cycles going. For this reason, indoor trees are usually placed under lights on timers, mimicking the gradual increase in day length hours as Winter passes towards Spring. When it comes to light requirements, the answer of “it depends” is highlighted. Study your plants, increase your knowledge about specific species requirements and adjust accordingly. Winter is a great time to read, study and watch You Tube videos to increase knowledge. That includes reading this blog and visiting http://www.bonsaiplace.net regularly for updates. Best still, subscribe and you will never miss an article.
Clean, clean and then clean some more. Get rid of leaves and everything else that all sorts of bugs can hide under, lay eggs, overwinter themselves and then come out in Summer and create havoc. This is also the time when you can spray to kill all sorts of fungal spores. A weak solution of lime sulphur does the trick. Just, as always, be careful when it comes to Pines when spraying for fungus as it can kill the beneficial micorhiza off in the soil.
In very cold climates most bugs and spores will be killed due to the very cold temperatures and for me the best is the architectural forms displayed by especially deciduous trees without their leaves. En joy this season, it is crucial in the development and normal growth of trees and also learn from your trees. We all need a break at least once a year.