It is necessary to have skills and knowledge about the treatment of wounds in Bonsai as pruning leads to the creation of wounds. Here we are not talking about the cutting of thin new or green growth, but more the structural pruning leaving larger wounds in more woody growth.
It is important that the tree is healthy before big cuts are made as it is stressful for the tree and critical that the conditions are maximal for optimal healing and growth. A free draining soil, good light, water and fertiliser are all requirements for good healing.
A cut from two angles showing some deadwood as well. All of that needs to be removed. This is also the opportunity to slant the cut so that it is less visible.
Both cuts on roots and cuts on branches and the trunk can be treated in the same way. What you need is:
A sharp cutter. I use a craft knife with replaceable blades. It needs to be very sharp and sterile.
Knob cutter or concave cutter. See tissue thickness requirements in the next paragraph.
Cut paste, either the putty type or the more liquid one.
If the tree has relatively thicker living tissue (cambium and outer layers), a concave cut needs to be made and if the tissue is very thin i.e. Azalea, then a convex cut can be made. Anything in between needs a flatter cut.
Start by using the cutters to either flatten or hollow the area of the cut wound. Use this opportunity to reduce the area by cutting at an angle or to the back of a branch.
Use a very sharp, sterile blade after most of the unnecessary material is removed.Rough cuts and most material removed.Smoothed out and ready for cut paste.
It is important that the cut area is as smooth as possible. What is meant by this is that a ridge in the middle of a cut will cause the new tissue to bulge over that or even stop the formation of new tissue. The living tissue (cambium outer layer) must be intact and the best way to do this is to run a very sharp blade across it. This will allow intact cells to multiply better and faster to grow over the open wound. Also referred to as the cambium rolling over the wound. Once the wound is clean, relatively smooth and the cambium prepared, use cut paste to cover the wound, especially the cambium. Proper cut paste will keep the cambium moist and it also contains chemicals that will enhance the growth of new cells.
Cut paste applied and you can also see the more acutely angled cut compared to before.
Allowing branches to elongate freely in the vicinity of the wound will help to bring nutrients and hormones to that area for faster healing.
Healing cuts with cambium rolling over. The edges of this cambium can be cut again to stimulate further growth until the cut is completely covered. The wound will eventually be fully covered and will continue to recover if the early steps were done right.
The area could be cleaned again after a few months of healing. Remove the cut paste and study the progress. If it looks as if the cambium roll over came to a standstill, gently open the edge of the cambium up again, apply cut paste and repeat the wait and check again process.
An almost healed large wound. This was about 3cm across as a wound.
It is a given. You will have a few trees die on your watch. Nobody wants it, but it happens and it is part of the life-death cycle that underpins all living things. We do not kill our trees deliberately and it therefore is important to take note of the things that do increase the chances of this unfortunate event.
Basic Horticulture
This relates to keeping the tree healthy through everyday practices, inclusive of hygiene, watering, light and nutrition requirements.
In my experience watering requirements is the most important of these aspects. Get that wrong and your tree will deteriorate and then just die. This relates to both overwatering as well as too dry conditions. Every tree will have different requirements based on species, soil medium, size and exposure to sun. Study this for each specie, make notes, learn and apply. Overwatering is the dangerous one as it generally leads to root rot and by the time you become aware of this it is too late. Be aware of irrigation systems. A power outage, a flat battery or a broken pipe, all lead to disaster. The best way to water is by hand and by studying each tree and adjust the amount of water to the daily requirements. It is labour intensive, but a safe way to keep your trees alive.
When repotting, pay special attention to the roots. Some species do not handle complete removal of soil well. Check for tangled roots, check for bugs, caterpillars and ants nests in the soil at this time.
Seasonal and Climate requirements
At the time of writing this, it is winter in New Zealand and after quite a dry period, it has now been raining for three days solidly and the temperature has dropped into single digits in places. Irrigation systems are now turned off and the focus now shifts from preventing trees from drying out to ensure they do not drown. Half of my trees now have pots at an angle to allow water to run off, rather than sit in the pot. Back to basic horticulture as your soil medium and its drainage ability now plays a big role in keeping trees healthy and alive.
Pot at an angle and removing excess moss for better drainage.
I have mentioned temperature and the accompanying conditions now come into play as well. Snow can actually insulate trees, but frost is just nasty. Your local climate and specific species will dictate if a tree needs to be under cover or not. Frost has killed many a tree. Very harsh high temperatures, accompanied with little to now sun protection and not enough water will kill trees. Take note of your pot and soil temperatures. The pot construction, size and colour can have an effect on the temperature inside the pot. Two pots next to each other can have very different temperatures.
Frost and cold damage.
Be careful when bringing plants inside, especially non-dormant trees. I have seen and heard of many trees that just did not like artificial heating systems, wood fire burners and even being cooked on a window sill, resulting in the tree ending up on the compost heap.
Light requirement of a tree is a big one. Suitable species for sunny areas are Celtis, Junipers, Chinese Elms, Cotoneaster, most Pine species, Holly, pyracantha and others. For a more shady aspect look at Azalea, Maples, Beech, Zelkova and others. Acclimatisation plays a big role here. You can gently and over time get some species to tolerate a wider range of light and temperatures if your care is spot on. Generally, if you get this wrong, a tree will deteriorate over time and if not corrected will say goodbye.
Seasonal differences and evergreen vs deciduous trees have different needs.
Overworking
This is not just a beginners issue. Many a tree has succumbed to being overworked. The safe mantra here is do little bits of work more often, rather than massive root work at the same time as huge pruning and styling jobs. This goes with seasonal changes as well. Certain things, like defoliation, should take place at a specific time of year. Same for root work and repotting. It could be different for different species. Study, learn and apply.
Diseases and Pests
That is self-explanatory. The best is to use preventative methods to stop disease and pests from getting to your trees. This could include preventative sprays, either organic or not. That depends on your philosophy, but either way, keep an eye out for tell tale signs. Things like ants can point to aphids, sooty mould and other issues. Yellowing and spots on leaves, droppings of bugs and caterpillars, chew marks on leaves, sudden leave drop, are all signs of things going wrong. Keep an eye out and this can easily be combined with your daily watering routine. A big part of prevention is basic hygiene around your trees. Get rid of fallen leaves, clean underneath your benches and check the undersides of pots. Many an issue can be prevented by just cleaning often.
Many places for creepy crawlies to hide.
Seal wounds, tie trees down in pots when repotting, check old wounds, look for new holes in the trunk, marks like ring barking and especially underneath the leaves.
Seal wounds.
Summary
This is just a snapshot of things that can go wrong and is not intended to scare or put Bonsai enthusiasts off, just a reminder that a Bonsai tree is like having a pet. The tree has basic requirements and if these are not taken care of, it will deteriorate and can then die as a result of neglect or just not being bale to pick up on adverse things early enough. The solution is to arm yourself with knowledge, practice the skills involved in keeping a tree alive and constantly take great care of your trees.
It is universally understood that old tree trunks and branches mainly consist of wood and not much of the softer stuff. To copy or create age in Bonsai, it is therefore desirable to have as much wood and bark as possible. These things do come with age and is very desirable in Bonsai, especially the bark, as that is the most visible part on trunks and branches and even on exposed roots.
Well formed bark
So what is wood? If you start peeling off the outer layers of a tree trunk or branch, you will find two kinds of wood underneath these top layers. Closest to the bark or outer layer is the sapwood. This is moist and a living layer consisting of the xylem fibers. These are tubes which help the tree to transport water and nutrients from the roots to the leaves. The mechanism for this is explained in other posts on this site.
Underneath this layer, you will find the harder layers called the heartwood. This is dead material and basically consists of the xylem tubes which are not hardened by resins and no longer transport water and nutrients. This is the wood of the tree and is easily recognizable by the annual rings.
Annual Rings.
Back to the external layers. On the outside of the sapwood you will find the cambium and this is where the growth takes place, thickening the tree and the source of the annual rings. On the outside of this, you will find bark forming. This is basically just the original epidermis (outer layer of cells of a young plant) that undergo chemical and structural changes over time to form the woody or corky dead tissue that we know as bark. This is brittle and not well fastened to underlying layers.
One of the important things to remember for Bonsai is that when we bend a trunk quite severely, you might here a bit of cracking going on. This is usually the deadwood and as long as you do not snap it completely, it does not interfere with the living parts of the tree, merely the structural bits. What you need to be careful of is to not break the outer layers too much as that is where the water and nutrients are being transported through.
To form a permanent bend in a branch or trunk, the wire will assist to keep the branch in position for the resins and dead fibres in a tree to settle in the new position and then hold it there. This is why you need to keep the wire on for a s long as possible, but at the same time be careful of the outer layers still growing and growing around the wire. Technically it is not the wire biting in, more a case of the outer layers growing around the wire.
We also have to be very careful with the bark. As it is an outer layer and not very well attached to the underlying layers of a very old tree, it can come off very easily. As pointed out earlier, it is desirable to have the bark on trees like oaks, redwoods and others, it needs to be protected. A few things to do is to never pick a tree up by its trunk, cover the bark with rafia when applying wire and protect the bark with sifter material when using guy wires.
Protect bark from guy wires.
Raffia.
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Lime Sulphur is usually used in the Horticulture industry to control scale insects, moss, lichen and fungal diseases on plants. It can be used for all of these issues when it comes to Bonsai. A use that is not listed on the container is to whiten deadwood / Jin.
As always, safety comes first when you use any chemical. In this case, it is not just the smell (rotten eggs comes to mind), but also the fact that this chemical is corrosive. It is a good idea to wear gloves and to protect your eyes. Wash your hands very well afterwards and keep your hands away from your face.
Follow the instructions on the container for all uses. As said, the whitening of deadwood is not listed as a normal use of lime sulphur. One thing to keep in mind is to also protect the soil surface from lime sulphur dripping or being spilt on the surface. Remember, this chemical is also used to kill moss! You do not want to kill of your lush green carpet covering the soil surface. I usually use plastic wrap for this purpose.
I dilute the lime sulphur 50/50 with water and I do this in a plastic or paper cup as it is easier to just throw it away afterwards than trying to clean it and getting rid of the smell. I also use a 12mm brush for most applications, but can go smaller or larger depending on the size of the job.
I also find it easier to apply if I slightly wet the surface of the deadwood. The Juniper that I worked on here had a bit of rot at the bottom where the tree meets the soil surface. This was cleaned well and the lime sulphur was liberally applied here. The chemical protects the wood against rot by acting as a preservative.
After application, clean the brushes well and get rid of the container. Wash your hands and allow the lime sulphur to dry and work its magic on the tree.
For us in the Southern hemisphere the leaves of our deciduous Bonsai trees are starting to change color and they will soon be on the ground. In the Northern hemisphere Spring growth is to be seen everywhere and I have noticed a proliferation of photos indicating just that on Social Media. The difference is that the daylight hours are getting less in the South and the opposite is happening in the North. Suffice to say then that it must be the availability and intensity of light that triggers these phenomena. Today I would like to explore the color changes in leaves during Autumn.
We know that there is a pigment in leaves called chlorophyll. It is the site where photosynthesis takes place in leaves. This is the process where water and carbon dioxide gas with the aid of light energy is converted into sugars for plants to use as food or to be stored.
As the days (light) get shorter, there is not enough light energy for photosynthesis to take place at optimum levels. The trees must rest and basically shut down and the only food available to get through winter, is what is stored. As this progresses, chlorophyll disappears from the leaves and the bright green fades away. Chlorophyll is not the only color pigment in leaves. As the green fades, the other color pigments become visible. These are the yellows and orange colors (carotenoids). In some trees, like maples, the glucose produced during photosynthesis gets trapped in the leaves and the sunlight causes the leaves to turn this molecule into a red color. It is known that the cooler temperatures have a role to play in this. There are other pigments present as well. Red anthocyanin pigments can also be produced during this time.
Currently, my trees, and especially the Maples, are not showing the bright red colors yet. This is late for this time of year. Our night time temperatures have not dropped sufficiently for this to happen. Other climatic factors play a role as well. What is needed for all the splendor of autumn to show in our Bonsai trees is a warm, wet Spring, followed by a Summer with average temperatures and an average rainfall as well as an Autumn with many sunny days and relatively cold nights. There is nothing we can do about any of these except for controlling water, but it might be possible to shift trees in one’s garden during Summer and Autumn to make use of micro-climates caused by other plants and the layout of your garden.
The old debate of whether Bonsai is Art or Horticulture is actually a non-event as we all by now know that a dead tree cannot be designed as a Bonsai and be admired as a living sculpture. We need both. The tree must be kept alive and sculpted to enable the Bonsai within to be shown.
I am in the process of re-reading a lot of my quite sizable Bonsai library. The majority of these books and magazines focus on the Art side of Bonsai cultivation. It is rare to find a good solid article or chapter in a book, dedicated to the Horticulture involved in Bonsai development. A quick search on the Internet shows more of the same. There is a bit more to be found on the Internet, but a lot of this is not necessarily linked to Bonsai specifically. A few examples are of importance here.
The first to mention is the practice of defoliation. When we remove the leaves from a tree, we drastically reduce the level of transpiration (loss of water through leaves), which is an important process supporting the flow of water through a plant. Partial defoliation obviously does the same, but just less. Then there is the practice of leave cutting. This will reduce the surface area of the leaves, which in turn will also have a reduced transpiration level as an outcome. Photosynthesis levels will also drop. There are very good reasons why we do this in the cultivation of Bonsai, but it is a process rarely seen in the cultivation of other plants.
Another of our Bonsai specific activities is the process of deadwood carving or carving in general. Deadwood is dead and nothing much needs to be taken into consideration except for aesthetic principles. When we carve into living wood, things change a bit. Tree tissues are laid down in layers. On the outside we have bark and under this we have the phloem, the tissue that conduct the nutrients produced in the leaves through photosynthesis. The next layer is the cambium. This tissue is responsible for the secondary growth in stems as well as roots. The next layer is the xylem. This tissue transports water from the roots to the leaves. Then we get to the lignin. These are dead cells and make up what we refer to as “wood”. This is the stuff we carve. To get to the lignin, we have to go through the living layers. This needs to be done carefully as we are interfering with some very important processes when we start carving. Not only do we interrupt the flow of nutrients and water, we directly impact on growth. This works well for us as well, as the cambium layer is the one that will help with the healing on the edges of the carving.
My advice is for Bonsai enthusiasts to read and learn about the science behind our activities as well. Not only will this knowledge help to keep more trees alive, it will help us understand the design process and principles better as well.
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