Tag Archives: Carving

Live Veins on Bonsai – do they exist?

Most bonsai enthusiasts will have come across the term ‘live veins’ in the context of bonsai. Live veins are areas of living bark surrounded by deadwood. They are often seen on juniper bonsai, where a section of bark twists around the tree in a dramatic contrast to the white deadwood (Sierra juniper are particularly amazing). But how does this actually work and is it a ‘vein’?

The bark layer on a tree contains the phloem, which is responsible for transporting photosynthates (sugars) and other molecules around the tree – it sits just at the base of the bark next to the sapwood. As new plant organs develop, a connected line of phloem cells is created so that sugars can be transported from these organs (if they are leaves) or to them (if they are sugar consuming organs like roots).

Phloem cells in the leaves connect to phloem cells in the branch, then to phloem cells in the trunk. They are long tubular cells with the main connection point for sap flow at the end of the tube, and minor connections in the sides. Below is an vertical image of sieve tubes of Cercidiphyllum japonicum (Katsura tree) – you can see the sieve tubes in blue, and their connections at a diagonal in dark blue. The brown cells are companion cells which help the sieve tubes to function. In this example there are some connections between the sides of tubes, but most of the connections are end to end.


Phloem & sugars preferentially flow along this natural end-to-end route. One research study looked at what happens when you block a phloem path by girdling. It was observed that initially sugar flow to roots from that branch stopped, then resumed partially by finding another route (probably laterally through the sides of the phloem cells), then the tree grew new phloem and resumed sap flow.ref

So what does this mean for bonsai? Basically – live veins (or more accurately, ‘live strips’) of bark can supply sugars to roots as long as they have phloem connections to sugar producers (leaves) and to sugar consumers (roots). What is really important is that we work with the orientation of the phloem cells when creating deadwood. Cutting across the grain of the phloem would sever the sap connections and be a form of ringbarking. Instead leaving a strip which goes along the grain of the phloem will provide a leaf to root connection. The phloem tubes will always be aligned lengthwise along a branch or on the trunk – ie. heading down to the roots. The variation you might see is that some phloem & bark spirals around the trunk and some goes straight down. This should be obvious from the bark pattern.

It’s also important to ensure there is enough foliage at the top of the live vein to meet the needs of the tree (or scope to grow more foliage). It’s useful to know that sugar from a leaf is prioritised for use local to that leaf. Leaves provide sugars for the developing shoot apex nearest to them, and flowers or fruit on the same branch; so from an energy perspective, as soon as it can be, a branch is self-sustaining. Lower leaves on a branch typically are the ones exporting sugars to the roots.ref This might be useful when thinking about deadwood creation and possible options for live veins.

If you are aggressive with your live vein creation, and remove a lot of bark, it’s likely that some roots will die. One way to minimise this is to maintain a reasonable bark/phloem coverage around the base of the tree, and to start the deadwood further up.

One final word – there isn’t really any such thing as ‘finding’ a live vein. All phloem/bark is live until you create deadwood above or on it. It’s more about creating the deadwood and leaving the live vein (or ‘live strip’) behind.

Carving Trunks and Branches

Most bonsai enthusiasts I know love a bit of Dremel action – a great way to add interest to a tree and to make it look like an old tree is to create deadwood like jin, shari & uro, or more informal natural-looking deadwood forms. For the art and craft of this you should look elsewhere – Will Baddeley at Wildwood Bonsai runs workshops on carving (and has a good example on a Prunus mume on his website). Let’s be clear that any carving you do to a tree is creating or shaping deadwood. You can’t carve a live branch and have it stay alive, at least not the part you carved.

But what does this physically do to a tree? That very much depends on where you are creating deadwood. If the part of tree you are carving is already dead, then carving it will not affect the tree (although, you then have deadwood to manage, see the end of this post). If you are carving live wood, there are some considerations.

Firstly, go back and remind yourself how xylem and phloem work. They transport water, nutrients and dissolved substances like plant growth regulators around the tree. Leaves ‘load’ photosynthates (sugars) into the phloem and roots load water into the xylem. The point here is that movement through these vascular tissues is required in order for water, photosynthates and nutrients to travel around the tree. If you remove these tissues by carving, it will affect at least some parts of the tree.

Xylem and phloem vessels are not usually just one layer wide and they don’t flow end to end like a pipe – there is movement between adjacent vessels and different ways for xylem and phloem sap to flow if areas are damaged. But if you carve away the entire phloem layer – which most likely you will when creating deadwood – that path for phloem sap is closed. Similarly for xylem – if you carve away active xylem vessels then water can’t flow that way any more. You need to understand what the effect of this will be for branches and foliage which you want to keep. If an area of the tree has its water source shut off – it will die. If an area of root has its photosynthate source cut off the same will happen.

Whilst its not true that trees have ‘veins’ exactly since they have multiple connected cells (more like a bundle) and not just one vessel like a vein, the bonsai parlance which refers to ‘live veins’ is approximately correct. If you can imagine a vascular bundle passing between leaves, trunk and roots, you’ll be able to work out what consequences any carving will have.

Apart from anything else, carving live wood will result in a wound, you can read about how trees deal with these in Repairing (?) damage.

Once you have deadwood, what does it mean for your tree? Well, dead wood which is exposed to the environment decomposes over time, through the action of so-called sapotrophic organisms (those that feed off dead organic matter). The decomposition of deadwood worldwide is a critical component of the global ecosystem, releasing nutrients and carbon into the soil and atmosphere.ref In the forest, fungi, bacteria, invertebrates (like beetles) and nemotodes are the organisms which decompose dead wood. Basidiomycota is the only type of fungi which is know to degrade lignin, a major component of woodref (the dreaded Honey Fungus or Armillaria is a member of the Basidiomycota family). Below is the mix of fungi and bacteria involved in decomposition of a European beech (Fagus sylvatica)-dominated temperate forest.ref

The rate of decay of deadwood in the forest is determined by environmental and genetic factors. Gymnosperms (conifers) resist decomposition due to the volatile compounds in their wood.ref Angiosperms which have distinct heartwood, including oak, take longer to decay for a similar reason – heartwood often contains substances which deter fungi and bacteria.ref A fun fact is that plants don’t excrete like animals do. Instead they store away toxic compounds in their vacuoles (fluid-filled spaces within plant cells which occupy up to 90% of the cell volume) (Hallé). Just some of the compounds stored in vacuoles include pigments in flower petals, latex, digitalis in foxglove, resins, alkaloids such as opium and the chemicals in garlic.ref So these compounds can have the effect of slowing down decomposition, by being extremely unpalatable to microbes.

From a bonsai point of view, you want to avoid your deadwood being colonised by sapotrophic organisms – or at least you want to slow this process down as much as possible.

One approach for keeping your deadwood fungi/bacteria load down is to apply some ‘extractives’ to the wood – extractives are volatile compounds found in heartwood and bark, which have anti-bacterial/fungal properties. There’s quite a good thesis online which identifies many extractives from a range of different trees – you could try turpentine for example, which is extracted from pine tree resin. I’d avoid putting this into the soil though, for fear of harming beneficial microbes in the rhizosphere.

One of the main accelerators of decay in young stumps is moisture content.ref This is a another key control you have to minimise decay in deadwood on your bonsai – keep it dry – or in scientific terms reduce its ‘wettability’. This can be achieved by applying something like linseed oil. Other substances I have heard applied to deadwood are superglue (it reduces wettability by creating an impermeable layer on the wood), and wood preservatives but most of these have chemicals I wouldn’t want washing into my bonsai soil.

So in summary – before you carve, work out what you’ll be doing to the phloem and xylem flows to avoid damaging areas of the tree which you want to keep alive, and once you have deadwood, keep it dry and repellent to microorganisms. And in order to help with wound healing, carving in warmer weather when the tree is in active growth gives it the best chance of defending against pathogens which try to enter via the wound.