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10 min read

With the shortest day behind us now I can safely say spring is on its way. This realization brings with it the need for planning for the season which begins to loom before us. Spring would certainly rank on any bonsai artists calendar as the busiest season of the year.

Its not all work though, after the cold and wet winter the warmer days bring with them new life in us and in our trees; a sense of new beginnings and perhaps {hopefully} rejuvenated ambition to really get stuck into your collection during the growing season which lies ahead.

Hackberry bonsai trees

Image caption. After having to look at our trees in the nude for the last few months, we have a canopy full of bright green leaves to look forward to in spring.

Make no mistake, there is a lot of work around in spring and this work is made that much easier if proper planning is done in time. There is nothing worse than waking one morning to find half your collection requiring immediate repotting as the buds have already begun opening and you have no growing medium prepared!

So please use the following list as a guide to help prepare:

Winter pesticide spray

If you have a collection of bonsai, they will usually be grouped together. This proximity between trees can lead to a buildup of pests and diseases over a period of time. If you haven't already done so I would recommend the age old method of addressing this problem by spraying lime sulphur.

What are the benefits?

  1. addresses all pest and disease issues which I am aware of
  2. breaks the cycle of these between growing seasons

Lime sulphur should be applied as a spray (and I mean the tree must be dripping with it!) to all trees, deciduous or evergreen. I spray twice, two weeks apart to be sure I have contacted all the surfaces and got the solution into all the cracks in the bark. It works best on scale insects when they are on the move so try spraying when it's not too cold (above 20deg C daytime maximum is advisable), and of course there should be no rain immediately after application.

Mealy bugs on bonsai lime sulphur

Image caption. Mealy bugs are sorted out by a repeated exposure to lime sulphur spray.

A lot of people are scared of using lime sulphur on unglazed pots. True, it does leave white stains on the pots for a few months but this fades. I also take no precautions to prevent the solution from getting into the soil, it will not do any harm to the roots or to the mycorrhiza that lives there in the case of certain species. You are not dipping the container and the amount of solution which will drip off the tree and enter the growing medium is acceptable.

Depending on who you speak to the concentration differs. I mix lime sulphur with water in a 1:15 ratio.

You can purchase lime sulphur here, or from your local nursery. Just remember that once opened to store it properly in an airtight container. Once crystals form in the container then it is useless and will need to be discarded.



When I think spring I cannot do so without immediately thinking of repotting. Soon after that, I recall plenty of sore muscles, being berated for constantly dirty fingernails or traipsing dirt into the house and always being in a rush.

Why we repot

  • Repotting is something which we are required to do with our bonsai trees, to keep them in a healthy condition.
  • Some growing mediums compact, retarding drainage.
  • Roots develop and eventually fill the small container again impeding drainage but also limiting water and oxygen penetration.
  • A build up of fertilizer residue alters the pH (making it more acidic) and may also contribute to the reduction in water drainage and exchange of oxygen depending on the type being used.

I am actually of the opinion that most people repot too frequently, although the frequency does depend on the species and stage of development. A young tree in development phase may require repotting every 2nd year, but a mature pine may only require repotting every 5 years or even less frequent.

One should never repot simply because everyone else is, it would be best to determine if the tree really needs it by considering the factors above and determining whether any of these issues are being experienced and if repotting is the only recourse. Sometimes there are other less invasive actions one can take, such as simply scoring the surface with a rake to break up the "crust."

Trimming roots on bonsai repotting

Image caption. Don't use your best scissors when cutting roots as stones damage the cutting edges.

Repotting Shopping List

Sufficient Growing medium

Must be fast draining and not too moisture retentive. Go through your tree collection and identify the trees which will need repotting this season and work out roughly how much medium you're going to need. Ordering in bulk will save you money, as opposed to repeatedly ordering small quantities.


Pot bound trees are difficult to get out of the pot and it is best to use a sharp implement such as a sickle to make a narrow gap between root ball and pot and thus be able to lift the tree. This is especially a problem when trying to remove a tree from a pot with a convex wall

Root hooks

A root hook is useful in loosening old growing medium and combing out the roots in developing trees.

Root hook in bonsai repotting

Image caption. A root hook or rake is useful for raking out the roots of the rootball and for getting rid of old "spent" growing media.


When a more mature tree requires repotting, a root hook is too coarse and a rake is needed to rake out the mass of fine roots

Drainage mesh

If the holes of a bonsai container are not covered with suitable mesh then it will simply wash through. Suitable mesh is a mesh which has an aperture slightly smaller than the graded growing medium you are using. Anything small and fine particles will be caught and prevent proper drainage

Soil scoops

A soil scoop is useful for transferring growing medium from a bucket or other bulk container to the pot without messing and it also makes it much easier to "place" than when trying to use your hands or other makeshift container.


I cannot stress it enough - USE WIRE TO ANCHOR YOUR TREE INTO THE POT. Failure to do so may result in your tree being lifted out the pot by a gust of wind, or at least allowing movement within the pot and thus breaking young, tender roots. Movement in the container, in my opinion, is one of the reasons a tree may suffer unnecessarily after repotting it.


A small broom of natural fibers is useful to spread growing mediums and in clean up operations after the repotting work has been completed.

The above is not an exhaustive list of tools which are useful when repotting. I would furthermore suggest a pair of scissors which you will dedicate to cutting finer roots only, and then a must have as far as I am concerned is a root cutter.

Take a look at this collection of items for repotting.

Repotting demonstration


The word bonsai includes reference to a container, although interpretation of what constitutes a container has become rather vague and abstract these days. I personally prefer to stick with the classic, fired ceramic container but please feel free to experiment if you like. 

Selection of bonsai tree ceramics

Image caption. It's useful to have a selection of bonsai pots to choose from come repotting season. In this way you can choose the best pot for the tree rather than use the only one you have.

If you're not sure how to select a suitable pot for your tree then please do read the in depth article I have written on the subject here.

Whatever you do decide to use as container; whether it be a ceramic pot or piece of recycled tire you should keep in mind the following:

  • Bonsai is about the combination of tree and pot, the pot being secondary to the tree and should play a supportive rather than dominant role.
  • A mistake I see all too often among beginners is that they put their trees into bonsai pots too early. {Read these articles on field growing}. If field growing is not for you, then "over-pot" your tree at least, to allow it plenty of space in which to develop and then as it matures and finer ramification is required, move it to an increasingly smaller container. However placing the tree in too large a container is simply a waste of resources as your tree cannot maximize the use thereof.

Shohin bonsai in small bonsai pots

Image caption. These shohin are planted in very small pots. This means that come summer time people are going to be watering up to 3 times a day. If you cannot maintain such a schedule you will either need to resort to automation; plant them in larger pots or consider humidity trays.

    • Planting your tree in too small a pot will mean extra work {watering} in summer. Use a pot of manageable size to suit your schedule.
    • Try to have an assortment of containers available to repot your trees into. When you are busy with repotting it is nice to have several pots which you can mix and match with different trees. {Read this previous blog post where I demonstrate what a difference a bunch of pots can make to the same tree}. A pot should enhance the tree, and it's usually very obvious when you find a winning combination. If you can't afford to buy new pots perhaps you can organize a pot swap meet with some bonsai friends.

Grafting Subjects

Every time I repot my maples I look at how I may improve their nebari. The fact is that when you repot, it is the only time you can perform a root graft safely.

Likewise thread grafting can only be done in very early spring when the sap is rising and buds are only just beginning to show signs of swelling.

Approach grafting bonsai trident maples

Image caption. Trident maples take very well to the approach grafting technique as they heal over so quickly and so readily.

What to prepare

Suitable grafting material

  1. Forapproach root grafts I generally exclusively use rooted cuttings of the same species which I took in autumn 2 seasons ago. {Read more about taking cuttings here} However you may also use 2 - 3 year old seedlings.
  2. For thread grafting you will need some long whips of the same tree or you can use a donor seedling of a few years of age. However bear in mind that if you use a seedling, the genetic characteristics may be different and so that branch might have a different leaf shape, it might have different autumn colour to the rest of the tree etc.

Cuttings to be used for approach grafting

Image caption. Rooted cuttings are useful to use as approach graft material in the root zone. However use branches from the same tree for approach grafts in the canopy. 

Tools you're going to need for root grafts

Grafting knife

For root grafting you're going to need a sharp grafting knife to create the groove in which to lay the scion. Grafting knives in general are very useful for cleaning cuts to accelerate healing.

Grafting pins

Grafting pins to secure the scion in place as it must absolutely not move. You can order pins here for grafting.

Panel hammer

Panel or other small hammer to hammer in the grafting pins.

Wound sealant

Sealer to ensure that the joint between scion and tree is kept from drying out. Some people claim that sealer prevented their graft from taking by coming between the cambium. If that is the case then they did not graft correctly in the first place as there shouldn't be such a large gap between the two surfaces to be fused in the first place. A good graft is one where the branch can remain in the groove without being held in place (You still need to anchor it there for the long term).

Healed wound on a chinese maple bonsai tree

Image caption. When a proper sealer is used, wounds close as they should like this one which was a large cut on a Chinese maple.

For thread grafting you'll need

Suitable drill bits

Suitably sized drill bit which will be at least 1 1/2 times larger in diameter than the thickness of the branch you will push through it. A power or hand drill will of course also be needed. Drill too small a hole and you risk breaking off all the buds as you pass the branch through the hole.

Wound sealant

Sealer ensures the point of contact between branch and trunk is kept moist or fusion will not happen.


The initial spring push of growth will be supported by fertilizer you gave the tree in autumn of the previous season.

Contrary to some thinking, it is a waste to feed in winter. Trees are dormant during winter and cannot absorb fertilizer hence why Autumn is one of the most important periods during which to feed.

In Spring pushing all those new leaves takes a lot out of the tree and so you need to begin replacing those lost nutrients.

How much fertilizer and when you give it will be determined by the stage of development of your trees. A young developing tree can get as much fertilizer as you can afford to give it from the beginning of the season. A mature tree on the other hand needs less, so you might start to give it some light fertilizer a couple weeks into spring and then gradually a little more as the season progresses. 

Everyone has their preference for what fertilizer they use. Generally the consensus is that organic is better than chemical types, not least of all as you cannot do as much damage with organic as you can with chemical fertilizer by dosing incorrectly.  You may prefer to foliar feed than to use solid fertilizers or drenches. It does not really matter how, only that you do fertilize. You cannot work on a weak tree, period!

Bonsaiboost results with olive bonsai trees

Image caption. A sachet of BonsaiBoost pulled away to expose the feeder roots growing up towards the bag to the source of nutrients. I have never witnessed this response to any other fertilizer.

If you want to know what I use then take a look at BonsaiBoost. I do also foliar feed every now and then using fishmeal based fertilizers such as Sea Secret and Seagro combined with root promoting Kelpak.

Need help? I offer one on one consultations in person or remotely. Book here.

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