The need to rootprune annually or not, will be determined by the type of potting mixture used or state of maturity of the bonsai. In order to increase trunk girth, young plants need to grow. The more quickly they grow the sooner the trunk thickens. In order for this to occur plants need an adequate supply of air and root space. In many mixes the air supply is limited hence the usual advice given is to repot annually.The volume of air in the potting mix will determine the plant rate of growth.

In a more open mix the roots will not need to lengthen to obtain their sustenance they do in a regular mix, consequently you may find the roots have not filled the pot at the end of the growing year.

This makes the need for annual rootpruning unnecessary, and the saving of your time actually benefits the plant at the same time.

Bonsai should not be considered a static art, but one that is constantly developing. New growth brings new development, so consequently new directions become obvious. Only when a good basic structure is established, can refinement begin, but that is another story.

Winter is the slow-down time of year in the cold temperate zones; too cold outside. Warm temperate where the winters are more kind to some, there is a lot that can be achieved. The usual advice is to clean & tidy the Bonsai, especially remove the fallen foliage. Sharpen tools & weed and clean etc. But it is also the time to assess your progress & plan your direction. It’s pleasant to bring into a sheltered, warm spot a bonsai at night after work, and ‘fiddle’ with it. Having removed excess foliage one can more unhurriedly easily assess its next step I think it’s also a good idea to go over the winter tips, the details were mentioned previously.Japanese Maples are better pruned & trimmed before the middle of July. Pines & Conifers should have the foliage & twigs removed back towards the trunk. Deciduous trees painted or sprayed with lime sulphur. 10 water to 1 L.S. Remove from the surface slime & liverwort if not repotting perhaps wash away the surface & replace with you fresh mix. Wire at the start of winter rather than later.

September in the Sydney region has seen the new leaves open with growth extending. Re- potting of most deciduous species has passed. I have mentioned before that if times for safe root pruning can be staggered it will enable a calmer approach to this very important task.In September the Pine species and in particular the black pine group prefers their roots cut back this month. The trend though, is to cut their roots in August along with the mass which is also a safe time, especially with just a few plants to work with.However most enthusiasts have far too many bonsai so the annual ritual tends to be a task rather than the enjoyment to both you and your plants. Last month I described root- pruning as the Bonsai elixir of life.

Although mentioning the re-potting of Black Pine (Pinus thunbergii) it also includes other members of the black pine family, possibly the most popular pines used for bonsai. The Red Pine, (Pinus densiflora). The Scots Pine, (Pinus sylvestris) and the Austrian Pine, (Pinus nigra).

The Mountain Pine, (Pinus mugo) which is also a member of the black group, is not a reliable variety for use in the Sydney metropolitan area. It requires much colder winters than is experienced here, and coupled with Sydney’s high humidity becomes an unwise variety to use. The sad aspect is the short needle and amount of branches and budding that make it an ideal subject for our Art.

The plant elixir of life is the reduction of the root system, which has the effect of restoring an ailing bonsai. It can also reinvigorate a healthy Bonsai, keeping it in the prime of life. An aged plant can remain young by occasionally shortening old roots: at the correct time of course and producing new young roots. This procedure extends eternal youth to an old tree. The right time for Sydney is now before, or at the onset of new growth, but definetly before leaf buds open (late winter in Sydney); the roots of deciduous trees are usually the first to be pruned. It is normal for growers to bare root and cut back quite severely. Novices tend to be afraid of the roots; perhaps thinking it is cruel. Knowing the effect of pruning the roots provides stimulation to the Bonsai can change ones’ attitude to this technique.
Although writing these tips for the Sydney, Australia region I am aware they are being read in sometimes vastly different climatic conditions. The timing for rootpruning in your area may differ from the time (August) that I suggest for Sydney. How to adjust your timing will depend on you plants’ break of dormancy. Simply apply your timing for your deciduous Bonsai.As the nights are becoming warmer in Sydney, the time should be beneficial for working with the Ficus family. Despite variations to the climate that makes a late start for the leafbuds to burst your plants should always be the indicators of the RIGHT time for them.Often one hears of people afraid to root-prune their broad leaf evergreen bonsai, the plant is always in leaf! when then is it possible & safe to cut back the roots? Others can’t understand why their broadleaf evergreen bonsai died after cutting the roots. The reason being the plant was already in new growth which of course: is too late. Mature leaves on a plant do not indicate new growth, be aware though, with many plants it is safer to cut roots at the end rather than the beginning of dormancy.

This is more critical where the winter temps. are too low for that particular plant.In milder conditions an open potting mix allows for possible winter repotting.

A porous mix, draining from the surface within 5 seconds; allows much more freedom.
In this case meaning small amounts of useful information for a particular period of time. Time or timing can be crucial for some bonsai techniques in order to obtain positive results. For instance, the time for safe cutting of roots seems to be puzzling to many, especially novices. Indeed, the more experienced are often hesitant with unfamiliar species.Some species are more tolerant of root disturbance than others and of these I will inform later. The safest general explanation is to ‘read’ your plant especially when following information from another part of the world. You can’t go wrong with most species by root pruning at the end of a dormant period, prior to the start of regrowth. This is indicated by the terminal buds swelling but before its outer sheath splits & exposes the new leaf, irrespective of the species. In this way when spring is mentioned it will mean different months around the world.By ‘reading’ your plant the bursting of new leaf buds will herald the TIME, be it late winter, late spring or even early summer will be the right time for you and your Bonsai.

Bonsai information does not always supply the reason for advice. In the continuing aspect of timing for the reduction of the root system statements can be like – oh! I root-prune throughout the year. What determines questionable success of such a statement will be the degree of root removal & is not in any degree sustainable root-pruning. Such ‘root-pruning’ provides no incentive or stimulation for increased vitality. I describe light or slight trimming as just tickling the roots, reserved for alteration of the shape of the root-ball due to change of container or easing into a slightly smaller one. This should be a one off convenient or aesthetic type of root- pruning.Conversely, something to consider about the crown of plants is the fact that constant light trimming of twigs & leaves weakens the plant whereas hard pruning into thicker branches stimulates even a weak plant.

Next ……………. How much root to remove.

We all understand the reason to root-prune will be to provide room for young roots to be able to extend, for what reason? I have been told ‘when one thinks their plant has acquired the ‘look’ of age (a future discussion?) the plant from then should hardly grow’. Whew! My question was “ how is that achieved?” I was informed- ‘no more root-pruning will keep it small’. Unfortunately some variation of this thinking is not rare.The actual fact is that it will depend on your expectation of what a bonsai means to you. The considerations are – a. To grow a plant in a bonsai pot so it can be called a Bonsai. b. To be able to maintain to horticultural perfection: a plant in a bonsai container. c. The previous -coupled with applied artistic techniques in order to reach; your work of Art.

In Sydney our deciduous plants should have been root-pruned by September as their leaves usually sprout in August. Now to continue with the non root-pruning effect. Bonsai in essence has long passed this once impractical adage, its consequence – stunting.In the past, the description applied to bonsai was dwarfing and stunting. Both terms are the antithesis of the vibrant growth that should be associated with bonsai. The roots of a plant left to its own devices in a pot becomes compact, eventually excluding all the air. When this occurs with no vigour reserves left; the plant perishes. So sad!. It suffered enduring a short life. A healthy bonsai has the potential to pass the ‘term of its natural life’ due to periodic root-pruning. The capacity to renew young roots on an aged trunk is the elixir of life to the plant kingdom. The best kept secret for strong healthy plant growth is the availability of a sufficient air supply.
Size is controlled by pruning & trimming. The periodic reduction of the height & width will keep the bonsai ‘small’ & this is achieved by pruning the trunk, branches & trimming the twigs. A healthy bonsai will be allowed to extend a little before trimming back the new growth, so it either returns to its original size or enlarges slowly. If you wish to increase the height of your bonsai, the container will, at some stage, need to be larger.When the bonsai becomes top heavy, unstable & easy to topple over, a choice has to be made as to reducing its size or potting it in to a larger container. The constant growth that thickens the trunk & branches, plus the art of pruning the top & the technique of pruning the roots is how a bonsai develops.

Dorothy Koreshoff.
Bonsai Koreshoff Nursery ©