Tag Archives: Ramification

Bonsai Tree Growth Stages

Most bonsai trees progress through stages of development, each with a different objective. In general the progression is thicken trunk -> achieve branch & root structure -> achieve branch, foliage & root ramification -> reduce leaf size -> evolve as branches grow/fall off. The faster we can move through the first few development stages, the faster we will have beautiful, well-proportioned bonsai – harnessing the tree’s natural growth is a way to speed this up. We also want to avoid doing things which slow down a tree’s growth during these phases, as this will mean it takes longer to get the tree we want. Read about how trees grow before starting at #1 below. Also consider what do old trees look like?

1. Trunk

Some bonsai enthusiasts collect mature trees for bonsai specifically so they can start with a thick trunk, following a collection process which minimises damage to the tree. The alternative is growing your tree’s trunk. Once a tree has its roots and foliage reduced in size in a bonsai pot, it won’t generate the energy needed to make significant sapwood additions and its girth will only increase by small increments every year. So you really need to be happy with the trunk size first before you stick it in a tiny pot. But – how big should a bonsai tree’s trunk be?

2A. Branch Structure & Overall Shape

Arranging the branches is what gives you the canopy and overall foliage shape that you’re after and the first step in this process is growing (or developing) the branches you want in the positions they are needed. Growing a branch starts with a new bud, which, unless it’s a flower bud, becomes an extending shoot and eventually a new branch. So firstly you need to work out where new buds will grow on your tree and then deal with the extending shoots as needed to get the required internode length.

You may need to remove some buds and shoots if they don’t help achieve the shape you are looking for – this should be done as soon as possible to avoid wasting the tree’s finite energy reserves. You have a trade-off to make here because leaving more foliage on the tree will provide more energy overall which contributes to its health and ability to recover from interference. However, growing areas of the tree which won’t be part of the future design is a waste of energy. You don’t want to remove so much of the tree’s foliage that it struggles to stay alive or develop the areas that you do want to grow out.

When you are creating your branch structure, often you will need to reposition branches – this is done with a wide range of different tools and techniques. A more advanced technique for adding new branch structure is grafting.

Sometimes the trunk itself or larger branches need a rework, to make them more interesting or to make them look more like old trees – for example adding deadwood or hollowing out the trunk. Usually this is achieved through carving.

2B. Creating a Strong Root System

The trunk thickening and branch structure phases both work best when the tree has lots of energy and so letting it grow in the ground or in a decent sized pot during these phases will get you there quickest. This also allows the roots to keep growing, but you want to understand about the role of roots, and root structure & architecture even if you still have your bonsai in a training pot. Particularly in this case, knowing about how to foster the the rhizosphere will help your tree stay vigorous. To maximise the roots’ exposure to nutrients and water you want to encourage Ramification of Roots (lateral root development).

Eventually it’s time to move the tree into a bonsai pot. This requires cutting back the roots, but as long as the roots are balanced with the foliage in terms of biomass, the tree should be OK. Root growth is usually prioritised outside of times of stem/foliage growth, and above 6-9 degrees C. So repotting might be best conducted at times that meet this criteria. Your growing substrate/medium is an important consideration.

3. Ramifying Branches & Foliage

Ramification is when branches subdivide and branch, giving the impression of age and a full canopy – and a well-ramified tree is a bonsai enthusiast’s goal. There are some techniques for increasing the ramification of branches and foliage. But not as many as there are for root ramification.

This stage also involves ongoing branch selection and reshaping (see 2A above). Another consideration is whether to keep or remove flower buds.

4. Reducing Leaf Size

An end stage in the journey to bonsai perfection is leaf size reduction. In nature, leaf sizes reduce relative to the biomass of the tree as it ages but since bonsai are small this effect doesn’t translate since the biomass never gets large enough. The tried and tested method for reducing deciduous tree leaf size is actually to practice one of the various methods of defoliation. A couple of others are covered here in reducing leaf size.

When to conduct these various activities depends on when the tree can best recover from them – which is a function of the Tree Phenology (or Seasonal Cycles).

5. Evolving Branches

Trees are not static organisms – they obviously continue to grow which is what we harness in the above steps. Part of this is that eventually branches may become too large for the design, or they may fall off (Peter Warren notes that Mulberry are known for this). As bonsai artists we want to have this in mind so that branches are being developed which can take their place in the future. This is an ongoing version of step 2A.

Pruning

Once your tree has grown in the general direction and shape you want, you can refine it through pruning. Cutting into a tree can affect its health & vigour, so it’s helpful to understand exactly what happens to a tree when you do this. A really excellent paper explaining the effect of pruning is available from Purdue University^ref but to summarise, pruning has the following effects on a tree:

it removes photosynthetic material (leaves) thereby reducing the tree’s ability to generate energy
it reduces transpiration (the evaporation of water from the canopy) and the rate of water transport up the tree
it disrupts the pathways of plant growth regulators, causing regrowth but also consuming stored energy
if the main xylem vessels in the trunk are cut, it causes embolisms which reduce the water carrying capacity of the tree
it exposes the internal vascular system to the environment where bacteria and fungi can enter (by causing a wound)
on some conifers, pruning the shoot or branch removes options for future bud growth because dormant buds and meristem tissue is often concentrated in the more recent growth

Minor Pruning

Minor or leaf pruning is used in bonsai to keep the shape of a tree according to a design, but also to create ramification and reduce leaf size (or, keep leaves small). As per point 3 above, pruning leaves drives the tree to refoliate and it does this by activating dormant or suppressed buds. In deciduous trees there is usually a bud in every leaf axil and this will go on to produce at least 2 shoots, so you also get increased ramification. With only stored reserves to use for refoliation, shared across twice as many buds, leaf size will be reduced. Read more in: ramification of branches and foliage.

Major Pruning

Major pruning which involves cutting off branches or significant parts of the foliage may have more impact on the tree. The first thing is that removing large amounts of foliage will reduce the tree’s ability to generate energy. It will also reduce the tree’s energy requirements but not by as much as is lost (since leaves are working for the whole tree and not just to sustain themselves). See this article: Defoliation.

Major pruning is often required to get the design you want for a bonsai. So is it better to grow out then cut back, or cut back then grow? Growing first generates lots of energy but also lots of wasted growth, which is eventually removed. Cutting first saves energy by directing it all to the places you want to develop on the tree, but it reduces the total amount of energy available for growth.

To test this look at the following calculation. If you start with two identical 50-leaved plants, and the goal of reaching a particular level of refined foliage in 5 years time, you have two options. Scenario 1 lets the plant grow unpruned all the way to the end of the period then has a major prune back down to the target level of foliage. Scenario 2 prunes every year, gradually building up to the target level. Although they start and end in the same place, the first plant has generated a whopping 195,250 ‘leaf units’ of energy for growth – 12x what the second plant has generated.

As much as 80% of the energy created by leaves is exported to the other organs of the plant^ref. These energy units could have been used in places that don’t eventually get removed in the ‘Cut’ scenario, such as thickening the trunk, storing reserves for stronger budding or refoliation.

The most obvious risk with major pruning is the fact that you are effectively wounding your tree. Read more about how it responds in repairing (?) damage.

What kind of pruning tools should you use? Learn about the difference between carbon and stainless steel bonsai tools here.

Ramification of Roots (lateral root development)

Lateral roots are ones which branch off from the main root – just like lateral or axillary buds aboveground. Lateral root development is how roots branch and ramify – similarly to stems, which ramify through bud initiation and stem growth. Encouraging strong lateral root development is a goal in bonsai, because we want to create lots of fine root mass to provide maximum exposure to water, nutrients and enabling symbiotic partners (fungi & bacteria); it also helps to stabilise the tree in the pot.

The below image is a nice one illustrating the development of lateral roots. The root grows from the tip – known as the root apical meristem (RAM), where new cells are created and the root tip is constantly extending. Above the apical meristem are pericycle cells which are preparing to initiate lateral roots, and above that these have been initiated and are starting to grow. At the top a lateral root emerges. The pale beige section in the centre labelled the ‘central cylinder’ is the location of the vascular bundle containing xylem and phloem.

https://images.app.goo.gl/E112RndafnE5jdNz5

I have been astonished while researching this post to discover just how many things can affect lateral root growth. My post on Ramification of Branches and Foliage had just three ways to improve ramification – dividing the apical meristem, pruning (in various ways) and applying cytokinins. In this post there are no less than nineteen different mechanism for encouraging root ramification! I’ll list them (x) as I go.

Before we look at each one of these, let me tell you about the ‘root clock’. The root clock is an oscillating cycle in roots which determines where lateral roots are formed – the spacing between them is dependent on the cycle time of the clock.^ref The way this works is through the oscillating expression of genes in a region close to the tip of the primary root, called the oscillation zone.

As with anything growth-related, our friends the plant growth regulators (along with genes) are involved. Auxin (1) promotes the development of branching lateral roots as well as adventitious roots (such as on air layers) whereas cytokinin (2) opposes these effects.^ref The formation of lateral roots involves both shoot- and root-derived auxin with the root tip responsible for lateral root initiation (the first step of creating a new root), and auxin from the shoot responsible for lateral root emergence (the elongation and growth of the initiated root).^ref The root clock is involved here because the back and forth gene expression causes programmed cell death at the root tip to happen periodically, which releases auxins back up the root and initiates a lateral root.

Ethylene (3) inhibits root growth, and brassinosteroid (4) and abscisic acid (ABA – some species only and in small amounts (5)) stimulate lateral root growth and elongation.^ref1 ^ref2 In fact there are complicated interactions between genes and plant growth regulators when it comes to roots with different hormone levels detected in different parts of the root, based on the differing roles they are playing in each stage of root growth. For more check out this article about tap roots which has a good diagram showing plant growth regulators (fig 2).

Other substances produced within plants which promote lateral root development include salicylic acid (6) and melatonin (7).^ref

Aside from plant hormones, the nutrients in the soil also affect the level of lateral root development – for example nitrogen (8): “in low-nitrate soils, patches of high nitrate have a localized stimulatory effect on lateral root development in many species, however where nitrate levels are globally high (i.e. not growth limiting), lateral growth is inhibited”^ref A phosphorus (9) deficit “favours a redistribution of growth from the primary roots to lateral roots”.^ref A sulphur (10) defiency “leads to the development of a prolific root system, usually at the expense of shoot growth…roots elongate faster than those with sufficient sulphate, with lateral roots developing earlier, closer to the root tip and at a greater density.”^ref

Lateral root formation is restricted when water availability is low (11), and somewhat surprisingly, when there is a lot of salt (12) in the soil more lateral roots form.^ref

You might not think that roots need light (13), but in fact light above ground is necessary for maintaining the oscillating signal of the root clock and for the formation of sites where lateral roots can branch off; an absence of light has a strong inhibiting effect on root elongation and branching.^ref This may be related to the point below about sucrose – light drives photosynthesis and the creation of photosynthates like sucrose.^ref

This intriguing study found that drenching roots in sucrose solution (14) “significantly increased lateral root branching and root formation compared with non-sugar supplemented controls.”^ref This may be because of effects on the rhizosphere vs the roots themselves. Just beware what you might attract if doing this in your bonsai garden as a sucrose drench sounds like an insect’s dream come true.

Several studies have determined that root pruning (15) encourages lateral root formation ^ref1, ^ref2 and that this happens most likely due to a surge in auxins after the root is cut. Similarly, synthetic auxins applied to roots of scarlet oak resulted in six times the number of adventitious roots compared to a control, and resulted in longer roots as well.^ref

Another way to increase lateral root formation is via encouraging arbuscular mycorrhizal fungi (16). Interestingly, the mechanism for this is that the plant root detects the presence of chitin in the fungi cell walls.^ref Chitin (C₈H₁₃O₅N) is “the most abundant aminopolysaccharide polymer occurring in nature, and is the building material that gives strength to the exoskeletons of crustaceans, insects, and the cell walls of fungi.”^refResearchers found that any source of chitin (17) had the same effect – including chitin derived from shrimp shells^ref Chitins can be found in many living creatures, including crustacean shells, insect shells (beetles, grasshoppers, cockroaches, blowflies), bat guano, resting eggs of Daphnia species, spiders, green algae, zooplankton (krill), phytoplankton and fungi.^ref1 ^ref2 ^ref3

On a similar theme (and maybe a repeat of 14) the presence of Pseudomonads bacteria has been shown to increase adventitious root development in tobacco.^ref

While reading a study about plant growth substances recently I came across (18) – apparently you can physically bisect a root apical meristem and it will become two autonomous RAMs.^ref

And lastly let’s look at two types of pots which affect root ramification: (19) if you use a white pot instead of a black, green or other dark colour, roots will be up to 2.5 times denser^ref, and if you use an air pot (20) they will have fewer circling or malformed roots but also less root mass overall.^ref

So let’s summarise all the different ways you can practically encourage root ramification in your bonsai:

Root pruning
Encourage auxin & sucrose production via photosynthesis (leave some leaves and give the tree good light)
Apply exogenous (from outside the plant) auxins – for example from compost or compost leachate
Drench roots in sucrose solution
Add and nurture mycorrhizal fungi and friendly bacteria
Add a source of chitin (as a vegetarian I can’t recommend any of the animal sources, but some other ideas include scooping the algae from your garden pond (or similar) or adding some mushrooms to your compost and adding that (or its leachate) to your pots
Bisect the root apical meristems (ie. cut them down the centre with a clean sharp blade)
- Use a white pot

Gymnosperm (Conifer) Budding

Gymnosperms relevant for bonsai include ginkgo and the Pinales order (Araucariaceae, Cephalotaxaceae, Cupressaceae, Pinaceae, Phyllocladaceae, Podocarpaceae, Sciadopityaceae & Taxaceae – this is explained in The kingdom Plantae and where trees fit in). Ginkgo is a special case described separately at the end of this post.

So what we’re interested in in bonsai is where lateral buds appear, and in particular whether they can develop adventitiously (or backbud). Angiosperms (flowering plants) are relatively easy to understand in terms of their lateral budding, as many species reliably produce a bud in each leaf axil (the axil is the place on the stem where the leaf is/was connected). In gymnosperms though, this is not as predictable and it’s not the case that each needle contains a bud – at least not in every species and not detectably. And looking at the different foliage forms below, you can see that different bud types must be involved to generate all these different leaf models.

https://cmg.extension.colostate.edu/Gardennotes/134.pdf

Many conifers have a terminal bud at the end of each long shoot/branch surrounded by a number of close lateral buds in what’s called a ‘whorl’. These include pines, spruce, fir, and the Auracaria family. The whorl in the picture is a Scot’s Pine, with a vegetative bud in the middle and reproductive buds around it. This will usually be the apical or strongest bud, receiving the majority of the sugars from photosynthesis.

https://joshfecteau.com/meet-the-pines-scotch-pine/#jp-carousel-8472

When the vegetative bud extends, it is called a ‘candle’ because it is a long thin structure – which looks like a candle. Below you can see a Pinus Thunbergii (Japanese Black Pine). Some candles are extending and some have extended and formed cones from the lateral buds around the main bud. No branching will occur from reproductive buds as they terminate the shoot.

https://www.conifers.org/pi/pi/t/thunbergii02.jpg

Bonsai enthusiasts commonly prune the candles to maintain a short needle length, this has the effect of arresting the needle growth; it is also possible to completely remove the candle, to force bud break at the base of the candle which results in smaller and more buds. In pines there are usually short shoot buds at the base of the candle – these will produce needle clusters in the future but no stem elongation. Breaking or pruning the top of the candle will activate these buds, which is good for ramification. If you want to continue developing the structure of the tree, you need a long shoot with a terminal vegetative bud as this won’t fall off.

As well as the terminal buds, pines sometimes have buds on their lateral shoots, between the needles, as well as internodal buds, which appear along the stem and not just at the end. These usually appear at the axil of the individual leaves on a long shoot/stem (Dörken, 2012).

Other conifers such as those in the Cupressaceae family (Thuja, Juniperus, Cypress) do not have whorls or needles, they have scale-type leaves in ‘branchlets’ (and needle-like leaves when juvenile). You can see below some examples of these which show the lateral buds forming from inside the lateral leaves (the leaves on the sides of the shoots). Since these branchlets squeeze a lot more leaves in, they have more potential for budding than do individually-leaved species such as Abies (fir) and Picea (spruce).

https://craven.ces.ncsu.edu/2022/03/conifers-with-scale-like-leaves-what-makes-a-leaf/

However one key attribute of species in Cupressaceae like these scale-leaved ones above is that just like pines they do still have differentiated short shoots and long shoots (Dörken, 2012). The short shoots are the individual branchlets, which abscise as a unit after a few years (detach from the long shoot and fall off). At the base of this short shoot is another bud waiting to generate a new shoot once the branchlet falls off. So new foliage will come from the leaves on the branchlet while it is active, and then from where the branchlet was connected to the stem when the whole branchlet falls off.

Conifers with individual needles such as firs and spruce, and needle-leaved junipers, have buds at the base of each leaf, but tend to bud towards the end of the most recent growth. Last year we dug up a Christmas tree from our allotment and I pruned the ends of most of the branches because it was too wide to fit into the house. The effect of this has been to stimulate the subordinate branches to bud – but again this has only happened at the ends of the branches (see below). Something about firs & spruces keeps the active budding zone at the end of branches.

As well as understanding the budding pattern, a key question for bonsai afficionados is whether or not a particular tree will backbud. That is, will it be possible to increase ramification and foliage density by encouraging axillary or adventitious buds to form.

Gymnosperms were traditionally believed not to resprout, with research in the past finding that buds are not present in leaf axils of conifers. Despite that, there are quite a few gymnosperms species which do, including the following. Some of these “do not have distinct buds at all; they produce new growth from meristematic tissue hidden under the skin of the twig” (Thomas, 2018) – this is known as an epicormic bud. This may be a false distinction since the meristematic tissue may just be early buds which are not developed enough to be visible.

Some Abies (fir)^ref including Abies nordmanniana^ref
Araucaria & Agatha species including including Hoop Pine^ref and Wollemi pine ^ref1, ^ref2
Cedrus (true cedar)^ref
Cryptomeria japonica (Japanese cedar)
Ginkgo
Juniperus^ref
Larix (larch)^ref
Metasequoia glyptostroboides (dawn redwood)
Pseudotsuga (Douglas fir)
Some Pinus (pines)^ref – but pines are notorious for losing their ability to bud anywhere other than on the most recent 1-2 years old stems. Brent Walston at Evergreen Gardenworks says with Pinus thunbergii that as long as there is still a living needle on a stem, if you cut the stem above it, that will force a bud at the needle axil.^ref This lines up with the idea that buds in pines are present under the leaf axil of long shoot leaves.
Taxus baccata (yew)
Sequoia sempervirens (coast redwood)
Sequoiadendron giganteum (giant redwood)
Taxodium distichum (swamp cypress – deciduous)^ref
Thuja occidentalis (sometimes called White cedar)
Thujopsis dolabrata (a Japanese species similar to Thuja)

So actually there are quite a few!

Some studies have indicated that “cytokinin sprays on conifers growing in the field can
increase the number of visible axillary buds^“ref and as a result this study concludes that “conifer leaf axils might not be as blank or empty, at least in recently initiated shoots, as they might appear to be. Cells in the leaf axils, while not forming buds, can maintain a meristematic potential and if they lose meristematic appearance, they may be
preferentially able to dedifferentiate into bud forming structures.”^ref

In ginkos^ref, axillary buds are present in the nodes of long shoots only, and these trees can backbud – below is an example of a ginkgo at the Seattle Japanese Garden – you can see new leaves sprouting from the bark of a well-established tree (from the longest long-shoot of all – the trunk).

I’ve also spotted this tree around the corner from my house in London – it was quite tall with all the foliage at the top of the tree – when I saw it cut back so severely I was sure it would die. There were only the tiniest of shoots here are there on the trunk. But in a matter of a few weeks it grew back profusely, which makes me think it must be a Thuja of some kind – perhaps Thuja occidentalis ‘Golden Smaragd’.

Finally another lovely example of conifer resprouting are the amazing dai sugi in Japan – these are Cryptomeria japonica which are cultivated for forestry purposes. The tree is encouraged into a multi-stem form with horizontal branches, which sprout new vertical stems. These are harvested over and over, and new stems grow. In this way the same tree has been used for forestry for hundreds of years without killing the tree. The technique is explained in Jake Hobson’s book Niwaki, which also includes a brilliant photo of bonsai dai sugi, which I think look bizarre but amazing. I have several Cryptomeria japonica at my allotment in the hope of creating something similar (although realistically the ones in this image are probably air-layered).

https://twitter.com/wabisabi_teien/status/1038034988841627648?lang=zh-Hant

Defoliation

There are quite a few research papers about tree defoliation because this can be caused by insects, creating a problem for the forestry industry. Defoliation is used on deciduous trees in bonsai to completely regrow a deciduous tree’s leaves, resulting in ramification and smaller leaves. This isn’t a practice for conifers, or at least, not for most of them, as many conifers simply can’t regenerate very easily and the effect will be weakening of the tree and not ramification. Although I must note here that my 2022 summer watering disaster caused a small larch forest of mine to defoliate and it looked fantastic after the foliage regrew!

Complete defoliation is a pretty drastic practice from the tree’s perspective and a double whammy – as not only does the tree have to use its stored energy reserves to regrow its leaves, it doesn’t have any energy coming in until those leaves are regrown. Defoliation significantly reduces the total stored carbon in a tree, and there is a point at which mortality occurs – one study found that once stored carbohydrates were less than 1.5% of the usual level, this will kill the tree.^ref

As described in this article about the effect of grazing animals, “Plants adjust to conditions of chronic defoliation and the associated reduction in whole-plant photosynthetic rates by altering resource allocation patterns and reducing relative growth rates.”^ref Although the article is focused on grasses, which are a different branch of the Plantae family to trees, it says that “root elongation essentially ceases within 24 hours after removal of approximately 50% or more of the shoot system…[and there is]…a rapid reduction in nutrient absorption”. So basically by defoliating 50% or more the roots will stop growing and nutrient absorption will reduce. Interestingly, several studies reported that photosynthetic capability of the remaining leaves on defoliated plants actually increases – perhaps a result of the resource allocation pattern change mentioned above.

The effect of defoliation is to force a deciduous tree to use the stored energy it has built up in the growing season straight away, instead of leaving it for the next season. Because of this, the tree doesn’t have the energy reserves to grow a full set of leaves at the same size it would normally, so it compensates by growing smaller leaves. Since this technique uses up stored energy, there isn’t much left for other types of growth, so it’s not a technique you would use if you were trying to thicken a trunk or grow branches.

This study^ref found that a 50% defoliation of prunus saplings reduced their growth rates for the following 5 years and brought forward bud burst for a similar period, while this one^ref found that larch recovered well from defoliation, but pinus did not. This one^ref said that partial and complete spring defoliation reduced first-year diameter, height, and volume growth of 4-year-old loblolly and slash pines.

This article says that “scientists found that growth was reduced in both half and entirely defoliated trees in the short and long-term…both half and entirely defoliated trees had less leaf area than control plants. Defoliated trees also allocated more carbon for storage than control trees with no defoliation.”^ref This suggests that defoliation in some way teaches your tree to divert resources to storage instead of foliage, not just once but into the future. Which means you really don’t want to do this while you are still establishing the branch structure and ramification because these will slow.

Interesting, Harry Harrington reports that some species don’t respond to complete defoliation by growing smaller leaves, instead they grow a small number of large leaves^ref. So overall a complete defoliation may be an unnecessarily unpredictable and heavy-handed way to achieve leaf reduction. One could hypothesise that defoliation of a tree which follows a fixed growth pattern (read more in Extending Shoots) might result in a greater leaf reduction effect, because buds and nascent leaves are not sitting there waiting to burst, they need to be completely regrown. But one could also hypothesise that this type of tree might struggle to regrow any leaves at all, depending on the weather conditions.

There are less drastic options than removing the entire foliage of a tree all at once – you can remove half of it for example, or do it in stages, so that new leaves can grow before the remove the next batch. It seems like you should be able to achieve a similar effect with constant low-level leaf pruning throughout the growing season, combined with bud pinching at the start of the season. A more gradual approach would allow photosynthesis and energy generation to continue, without stopping root extension and nutrient uptake, while still regrowing leaves and increasing ramification. It may be however that the shock of something more drastic is what’s needed to reduce leaf size significantly because the resources to regrow are shared more widely. An experiment for someone?

The timing of defoliation is really important. The tree needs to have had enough time with its new leaves to generate good energy stores for the next season and enough time to regrow and harden its leaves against frost. Somewhere in the middle of the growing season allows for both of these to happen^ref.

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.