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Ramification of Branches and Foliage

After establishing trunk and branch structure, ramification (a fancy word for ‘branching’) of branches and foliage (as well as roots) is a key goal of bonsai. This makes a tree look older and more sophisticated, and gives the bonsai enthusiast options for continued development of the tree.

Ramification is created by branching the stems. Stem branching usually* requires buds, as a new bud creates a new stem. The pattern of stem branching for a particular species will depend on its ‘phyllotaxy’ (leaf morphology) and pattern of buds.

Usually in bonsai we don’t want more than two stems from the same location, the general guidance is to fork into two at any given junction. This is because strong growth of multiple branches at a junction leads to a bulging area on the trunk which bonsai judges don’t like. In the real world, many trees have reverse taper and bulging branch junctions though, so it’s your call. To avoid this situation, remove buds which are in places you don’t want by rubbing or cutting them off.

To improve ramification, you need to encourage as much budding as quickly as possible, then select the buds you want to develop. Pruning the growing tip is the main way to encourage budding, because pruning removes the apical bud (the dominant bud at the end of the stem), diverts resources into buds lower down the stem and sensitises those buds to respond to auxins and develop into shoots. In deciduous trees this should result in at least two buds generating from the stem instead of the one which was there. Another great way to create ramification on deciduous trees is through bud pinching – see Harry Harrington’s detailed explanation of how to do this. Bud pinching removes the entire primary meristem except for two outer leaves, this encourages the buds at those leaf axils to grow, along with two new buds at their bases.

Different species have differing abilities to respond to pruning, so try to get a sense by observing your tree of how well it will cope. Deciduous trees are designed for regeneration so in general they take pruning reasonably well, although if you take it too far they might send out suckers instead of new buds from the branches. With evergreen conifers you want to ensure there is some foliage and at least some buds remaining after you prune, otherwise it may not regenerate (unless it’s a thuja, or a yew, these guys are refoliating machines). I have cedrus seedlings in my collection and by cutting back the apical leader from not long after they germinated, and every year since, they have become extremely bushy and well-ramified (although, at the cost of developing a think trunk).

Gratuitous image of one of my cedar bonsai

Anything which stops or prevents tip extension will drive bud activation and ramification further back on the tree. In the case of conifers, the presence of flowers on the growth tips (as you see in juniper) has this effect as well, and can cause back budding. Lammas growth (a second flush in summer) can give you another round of ramification as long as you’ve pruned beforehand (otherwise it will just add to the existing stems).

Research has found that bud outgrowth is “controlled by plant hormones, including auxin, strigolactones, and cytokinins (CKs); nutrients (sugars, nitrogen, phosphates) and external cues”.^ref In particular the sugar sucrose has been identified as a key driver for promoting bud outgrowth and accumulating cytokinins – this is generated by photosynthesis.

In one study on apple trees, foliar application of a synthetically produced cytokinin 6-benzylaminopurine (BA) was found to generate three times the lateral bud growth on currently growing shoots compared to controls (but not on old growth)^ref and at the same time reduced the length of the main stem. BA was used to encourage better growth of bean sprouts in China before being banned^ref and has been shown to increase the number of leaves (ramification!) on melaleuca alternifolia trees^ref (melaleuca is the source of tea tree oil), and on some conifers^ref. Could BA (also known as 6 BAP) be useful in bonsai? You can (like most things) buy this product in foil bags on ebay, but there is a product in the orchid world called Keiki paste which also contains 6 BAP – so maybe some judicious use of ‘crazy keiki cloning paste‘ might also help ramification and shoot development in your trees?^ref You can also purchase BAP (as its also known) from vendors involved in hydroponics and suchlike as it’s used in in-vitro plant micropropagation.

If you baulk at paying £18 for 7ml of keiki paste, there is one other source of cytokinins which is a lot cheaper, more sustainable and clearer in its provenance – compost. This study found that compost created particularly from waste collected throughout spring^ref contained 6 BAP. Frustratingly there weren’t any free to read articles analysing compost leachate for cytokinin content, but if it’s in solid compost it’s a fair assumption there are cytokinins in leachate as well. Which makes me feel a lot better about the £300 I recently spent on a Hotbin composter! Which incidentally, produces gallons of leachate, which can be diluted and added as a liquid fertiliser.

* I’ve recently read a study which states that “apical meristems can be surgically divided into at least six parts and these then become autonomous apical meristems.”^ref What this suggests is that you could slice growing tips into 6 (or better, two since we don’t want more than two stems from a node) and they would become two stems instead of one! One to try next spring.

** By the way – it’s not auxins which cause apical dominance! Check out page 215 of this book, it’s nutritional status and phyllotaxy which determine the apical stem’s sensitivity to auxin which is present.

Shoots

This is a rewrite of my original post on shoots, now I know a *lot* more…

So what are shoots? They are the vegetative growth which comes from buds, extending to create new stems. Since stems create the architecture of a tree, shoots are really important when it comes to bonsai.

There are three key concepts to know about when it comes to shoots. The first is the existence of long and short shoots, the second is the way in which different shoots are formed and the third is the concept of the internode.

I had never heard of long and short shoots before researching this site, and I have since found that many articles and books don’t really talk about the fact that many species of tree possess two types of shoots. Shoot differentiation (as it’s known) is present on the vast majority of deciduous angiosperms (flowering trees), all deciduous gymnosperms, and quite a few (around 25%) of evergreen gymnosperms as well, particularly conifers.^ref

In these trees, two different types of shoot develop – long shoots and short shoots. Long shoots are exactly as described – they have a terminal bud which continues to build up the length of the shoot over time so it becomes (relatively) long. Short shoots meanwhile don’t persist beyond a limited number of years, they are much shorter than long shoots and have many fewer nodes. Both types of shoots can have leaves, flowers, cones and fruit, but only long shoots can create the long-term architecture of the tree. Importantly, aside from their structural trunk and branches older trees mostly grow short shoots, which is why they look more ramified.^ref

In some species (such as pines), short shoots – otherwise known as fascicles – are a feature of the mature vegetative phase of the tree, and don’t appear in the juvenile phase nor with juvenile foliage. An interesting side note is that fascicles can be used to propagate trees with needle leaves, the fascicle is treated like a cutting and placed in rooting hormone and well drained medium – the reason this works is because the fascicle is actually a short shoot and not a leaf.^ref

Below is an example of Cedrus libani where the clusters of needles (N1) are on the short shoot (S), and occasionally along the long shoot (L) there are individual needles (N2).

https://www.researchgate.net/figure/Shoot-and-needle-characteristics-of-Cedrus-libani-A-Approximately-6-year-old-spur-shoot_fig1_303469784

A fascinating – and useful for bonsai – attribute of short shoots is that they almost always have more leaves than the equivalent long shoot. In angiosperms, short shoots have multiple smaller leaves with an almost identical leaf area to a single leaf grown from a long shoot (see example A below).^ref And in gymnosperms short shoots have many more leaves and leaf area than long shoots – examples D and E below show the leaves on a short shoot (right hand side) compared to the individual long shoot leaves (left hand side) on larch and dawn redwood.

(source: https://beckassets.blob.core.windows.net/product/readingsample/10943560/9783510480326_excerpt_001.pdf)

So hopefully you can see that short shoots are fantastic for ramification! But not so fantastic for building the structure of the tree, since they don’t persist. So how can you tell which is which? Very simply short shoots are smaller, have a lot more leaves, and fall off when their time is up. Often in gymnosperms they will have cones at the end of their leaves.

You may not have realised that whilst the ‘leaflets’ on Cupressaceae species such as dawn redwood, cypress and juniper may appear to be compound leaves, instead they are actually short shoots. When their life comes to an end, the entire short shoot abscises (falls off) along with its leaves. Similarly for pines, what you might know as ‘fascicles’ are actually the short shoots, and on pines only the short shoots bear photosynthesising leaves (needles). Eventually they will fall off.

In angiosperms, a short shoot usually develops from the bud in the leaf axil of the long-shoot leaf, arriving the next season. In gymnosperms, it depends on the species. In Cupressaceae a bud will be sitting at the base of the short shoot so another one should grow once it falls off. In Pinus short shoot buds sit in the long shoot leaves towards the base of the long shoot, and they are positioned at the base of the long shoot bud.^ref In Ginkgo both short shoots and long shoots can come from any bud on any type of shoot.

Below is a picture of some interesting behaviour I’d never seen before – this Japanese larch belonging to a member of my bonsai club produced buds and new stems right through the middle of its cones. Pollen and seed cones on larch are terminal organs growing only on short shoots^ref – which means they aren’t supposed to extend. But Larix is known to be able to change the type of shoot from short to long if damaged (which may have been triggered by the hard pruning it received).^ref So in this case what had been a short shoot destined to eventually fall off, instead turned into a long shoot.

So what does it all mean? From a bonsai point of view, the first thing is to work out if a tree has shoot differentiation. If it is deciduous, it will, and if it is a gymnosperm, it still may even if evergreen – gymnosperms which have shoot differentiation include Pseudolarix, Taxodium, Sequoia, Cedrus, Larix, Ginkgo, Pinus & Metasequoia. Understanding the difference between short and long shoots will allow you to understand where foliage will ramify, and where the long-term structure of the tree can come from. On trees which don’t have shoot differentiation, any stem which has a vegetative bud can be used to develop the shape of the tree.

So now we know that long and short shoots exist in many trees, let’s turn to how those shoots form. According to Thomas (2018) , there are three options.

Option 1 is ‘fixed’ or ‘determinate’ growth. These trees preform every part of the shoot in the bud, so they extend very quickly (a few weeks) and then stop. If they are young (less than 10-15 years old) and have the right conditions, they may do this a second time around the start of August (in the Northern hemisphere), this is known as Lammas growth. The shoots from these trees developed based on the conditions at the end of *last year’s* growing season.

Option 2 is ‘free’ or ‘indeterminate’ growth. These trees have only some preformed leaves. Once extended the shoot will continue to produce other leaves from scratch in a continuous fashion. Often these are found in the tropics or warmer climes (my potted Eucalyptus never seem to stop producing leaves even during winter).

Option 3 is ‘rhythmic’ growth. These trees extend in recurrent flushes, with multiple cycles of growth and bud formation during the season.

Outside of the tropics, towards the end of the growing season all trees will stop shoot and leaf growth according to their phenology, in order to complete the formation of buds for next year. If conditions are not good, these buds will be fewer and contain fewer leaves. To see a list of which trees have which types of growth see the Growth Types Table. The relevance to bonsai is that trees with determinate growth are only going to give you one or at most two cracks of the whip in a given season. Those with indeterminate growth might be easier to develop since they will keep extending as long as the conditions are suitable.

Interestingly one study on lammas growth (second flushing) found that 73% of this occurred from lateral buds. We’d obviously love to have this in bonsai as it helps ramification within the same growth season.^ref This article^ref summarising lammas growth factors says that it can be encouraged by warmer temperatures (Pinus densiflora), extra watering (Pinus sylvestris), nitrogen fertiliser (Pinus sylvestris, Pseudotsuga menziesii) and applying a blackout treatment for less than 2 weeks early in the summer (Picea abies). So from a bonsai perspective see if you can encourage second flushing to generate those lateral buds.

And finally we come to internodes – these are the length of the shoot between each successive leaf. In general bonsai afficionados are looking for short internodes so they can achieve compact, dense foliage. The factors which affect internode length when a tree grows are the same as for any other type of growth – genetics, plant growth regulators and availability of nutrients. Shorter internodes can be achieved by (1) shoot pruning, (2) thigmomorphogenesis and (3) starvation.

If you allow a shoot to extend naturally (and it has no competing stressors), it will prioritise resources into growing as long as it can and the growing tip will suppress the growth of any lateral shoots below it – because the driving force for a tree is to grow large and establish the biggest exposure it can to sunlight. An angiosperm will grow a series of internodes with leaves at each point. What I have observed from looking in my garden is that the internode length on an angiosperm tends to start small (or in some cases leaves are grown directly at the node as well), then increase in size, then reduce again.

To get the smallest internodes, you should prune off the growing tip once the first pair of leaves and the first internode has grown. If leaves have grown at the node, you could remove the shoot altogether (there will be no internode in this case). New shoots will grow from buds in the leaf axils, and if you keep doing this, you will always retain the short first internode and increased ramification.

You could also make use of thigmomorphogenesis which is “the response of plants to mechanically induced flexing, including the brushing or movement of animals against plants, or the flexing of above ground portions of a plant by wind, ice, or snow loading”^ref According to this article^ref, “the most consistent thigmomorphogenetic effects are a reduction in shoot elongation and an increase in radial growth in response to a flexing stimulus resulting in a plant of shorter stature and thicker, stiffer stem.” i.e shorter internodes and thicker stems.

Thigmomorphogensis is thought to be triggered by plant growth regulators or other substances within the plant signalling when it has been touched^ref. To trigger thigmomorphogenesis in your tree, you could expose it to wind while the buds are developing, rub the internodes for 10s daily (seriously, this is what they did in the original study^ref which identified the phenomenon), touch the leaves regularly or manhandle the growing shoots.

Another way that bonsai enthusiasts encourage small internodes is by starving the tree. Fertiliser helps the tree grow and this will lead to longer internodes and larger leaves. Holding back fertiliser may result in the desired effect – but also could impact the tree’s health negatively – so it is a balancing act.

So there you have it – shoots turn out to be surprisingly interesting. For your bonsai, try to work out if your tree is shoot differentiated, and if it is, aim to use long shoots for structure and short shoots for foliage ramification. If it has determinate shoot growth, you need to work with the one or two shoot extensions that you get per year, and to get that second flush with lots of lateral buds try using one of the techniques above (warmer temperatures, extra watering, nitrogen fertiliser). Finally keep internodes small with judicious pruning, foliage fondling and holding back fertiliser.

Buds

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Buds are the “small lateral or terminal protuberance on the stem of a vascular plant that may develop into a flower, leaf, or shoot.”^ref Buds are responsible for primary growth, and are created by meristem tissue (a meristem is an area of stem cells which differentiates into different types of cells).

If you look inside a developing bud, you can see the starting points of the different cells which will arise – they can be vegetative buds (shoots & leaves) or reproductive buds (flowers in angiosperms or strobilus/cones in gymnosperms). Below is an image of a Jack Pine terminal bud which has many lateral vegetative buds on the sides.

https://botweb.uwsp.edu/anatomy/images/budanatomy/pages_c/anat0999new.htm

When shaping your bonsai, you want to know where buds may appear, so that you can encourage the direction of growth and shape you desire. Predicting bud location is relatively easy in angiosperms, which follow a relatively reliable pattern in their growth. Bud growth is more unpredictable in gymnosperms, but many of the following guiding principles remain.

Firstly, there are different bud positions:

The terminal bud is at the end of a stem or branch and this is the growing tip which makes the plant grow larger.
Axillary buds develop along the stem during the annual growing season according to the architecture of the tree (see below for more); within this, preventitious buds are axillary buds which are dormant and then develop in a later season.
Adventitious or epicormic buds are buds which do not develop according to the repeating architectural pattern – they arise spontaneously from previously non-meristematic (growing) tissue which can be anywhere on the tree. They are unpredictable as described in this post.

Below are some examples of angiosperm buds. The terminal bud is on the end of the shoot, this comes from the shoot apical meristem (SAM). Then there are axillary/lateral buds which occur along the shoot – in angiosperms these develop in the leaf axils (a position adjacent to where the leaf is attached).

Bud behaviour depends on a tree’s architecture, which is genetically determined – that is, it will be very similar for trees of the same species, albeit also affected by the environment. There is a lot of research out there about tree architectures, much of it pioneered by Halle & Olderman in the 1970s, there is even a mathematical model which can be used to represent the architecture of a given species^ref. As explained in this excellent article^ref, “regular development of each plant represents the growth of repeating units – ‘phytomers’…a typical phytomer consists of a node, a subtending internode, a leaf developing at the node sites and an axillary bud (also called lateral buds) located at the base of the leaf”.

Each type represents a pattern consisting of a shoot with one or more leaves in the same arrangement. In some trees growth is repeated in a sustained way throughout the growing season (a single flush of leaves), whilst conditions are right. In others there are alternating growing and resting stages (multiple flushes of leaves). During the resting stage, new leaves and shoots are being created inside the bud^ref. I’ve copied some of the main architectural models into this post: Tree Architectural Models

An important part of the phytomer pattern is the leaf arrangement, known as the phyllotaxis. Leaves can grow singly at one position on a stem, or they can grow in whorls where two or more leaves appear at the same position arrange around the stem. When leaves grow singly they spiral around the shoot to optimise their light capture – apparently using the ‘golden angle’ of 137.5^o ^ref.

The leaf arrangement on your tree is important because each leaf axil (the base of the leaf) should be the location of an axillary bud (although in gymnosperms these can be missing). These are key to bonsai because they become new shoots (with leaves or flowers). They develop in the position just above where a leaf used to be; when it falls off, a scar is left and a bud generates above the scar.^ref In fact what is happening is a continuous bud genesis, so when you have a bud about to burst, it already has embryonic buds developing at its base – this is why buds look like they form at the leaf axil (in fact they formed on the previous bud). Your new branches and leaves will generate from these positions, and dormant buds may be located here. Read more about buds in angiosperms here, and in gymnosperms here.

The growth of an axillary bud (and its embryonic buds) can be suppressed by its neighbours – this is how ‘apical dominance’ works. It used to be thought that in apical dominance, the shoot closest to the sun emitted hormones which suppress the growth of buds lower down the plant, ensuring that it gets the most resources. This research group at Cambridge University study the development of axillary shoots and their research says “shoot apical meristems compete for common auxin transport paths to the root. High auxin in the main stem, exported from already active meristems, prevents the activation of further meristems”^ref. This results in axillary buds going dormant and becoming ‘preventitious’ buds, but they are still available to grow later if conditions change. According to this article, apical dominance in trees only works on buds in the current year of growth due to the slow movement of the hormone auxin through the tree^ref – meaning that current year buds on a branch are suppressed by the terminal bud on that branch and not by the main leader. HOWEVER, it has recently been found that auxin does not move fast enough to have this effect, and instead it is driven by sugar flows to the apical meristem.^ref The effect of apical dominance remains, however it is now thought that sugar flow drives this and not auxin directly.

Encouraging axillary bud growth is a way of increasing ramification on a bonsai, as it can create multiple shoots instead of just the terminal buds. If the terminal buds are removed, axillary buds get the chance to grow, often more than one.

Application of exogenous cytokinins (benzyladenine) has also been shown to increase bud initiation^ref (see my post on ramification of Branches and Foliage for some substances containing benzyladenine).

Equally, looking at how the leaves are arranged, you can work out where new shoots will arise from existing stems. By removing the buds or shoots not meeting your design, you can encourage shoots to grow in the direction and position that you want. But it’s not enough to know about bud position, you also need to know what kind of bud is present – a vegetative or a reproductive bud, and you need to know the difference between short and long shoots – more here.