Background

As we are nearing spring repotting time I felt inspired to write the following blog in the hopes that it might result in someone trying out the techniques which I shall now share, as early spring is the best time to attempt them. I have not tried these techniques with any species other than Trident maple, although theoretically it should work just as well on any species which heals over easily.

Technique 1 - Root/Approach graft variant

I use the term novel because I have not read of or seen this technique being used elsewhere, not that I am suggesting I invented it either. Nevertheless how I arrived at the technique was totally by accident. I had a Trident maple which had a rather slender trunk with no taper. Normally I would choose one of two options; stick it into the ground and grow it on (Read more about field growing here) or accept it as is and work with it. Then I thought "But what if a third option exists?" Grafting works so well with this species, so what if I did a variant of a root graft and instead of only allowing the fusing to occur in the root zone or ground level I allow the trunk of the scion to fuse with the trunk of the rootstock?

Preparation of the scion

Your scions {its a good idea to do several of these grafts at a time, so prepare at least two scions} will be a young seedling or sapling of roughly 3 or 4 years old, although any age would be fine provided it is flexible enough to be bent when you tighten it up to the trunk of the rootstock.

It is best to perform this technique at the time when you would typically repot this species, which is when the buds begin swelling and are about to burst - or thereabouts. 

Remove your scion from its container or bag and remove all the growing media. Eliminate all the roots from what will be the inside or side closest the rootstock.

While you prepare the other scions and the rootstock you can immerse the scions in a bucket of plain water to keep them from drying out.

Just before you intend bringing the scion together with the rootstock you will need to use a sharp knife such as a grafting knife or blade to gently scrape the bark off exposing the green cambium beneath. However do not do this until you are ready as you don't want to expose the cambium any longer than necessary as this risks infection or drying out. 

Preparation of the rootstock

The rootstock will be an older Trident maple trunk, in other words it should be considerably thicker than the scions you intend grafting onto it. The ideal subject of this technique would have less taper in the lower part of the trunk than you would like.

Remove the rootstock from its container and prepare it as though you were going to repot it, in other words remove all the old growing media and if necessary you can root prune at the same time. In fact whenever I repot I use this rare opportunity to work on the roots of the tree in some way; whether it be to do some grafts, prune them to improve the ramification or to eliminate/split surface roots which are or have become too thick.

Its also a good idea to have a spray bottle on hand filled with plain water to keep the exposed roots moist while you complete the grafting process. 

Preparation of the container

Once the operation is completed you can plant the tree into pretty much anything whether it be a ceramic training container, a plastic training tray or a wooden box (Read this blog for ideas on how to make one). However I would advise against using too small a container as you will want to encourage sufficient growth which will aid fusing of the scions to the rootstock.

For a growing medium you can use your usual growing medium, whatever you would normally use to grow your bonsai in however I would recommend Professional mix as it is free draining but has good water retention ability. Ensure you have sufficient growing medium prepared so that you can complete the potting process once you have begun.

Other items you will need

You will need a few cable ties, yes this is one of those few times where I have found a use for these otherwise abused {in bonsai} modern fix-all's. The length of the tie will depend on how thick your rootstock is, otherwise you can join several together to form a single longer tie.

A good sealer such as Kiyonal sealer is needed to seal the grafts once you have made them. This is extremely important. Without a good sealer your grafts will be exposed to infection and to air, which will cause the cambium to dry out and thus fusing will not occur. And in case you are wondering, the answer is no, wood glue is not a tree sealer it is a glue intended for wood joints not for grafting.

A set of soil scoops makes life easier and speeds up the process of filling your container with growing medium, without spilling any. Also, be sure to cover the drainage holes of your container with suitable drainage mesh to prevent any of it pouring out the bottom and slugs getting in. 

Performing the graft

With preparation complete, plan where you will be making the grafts and mark the positions with a marker. I usually start by grafting on the left and right side, followed by the front and back sides of the rootstock a year or two later. If you have a pair of helping hands you can do all 4 at the same time, otherwise I can tell you from personal experience that it gets tricky! 

Gently scrape away the bark on the first scion and the spot on the trunk of the rootstock where you want to place it. Remember you only want to scrape off the bark enough to expose the cambium, if you go too far and expose the white wood beneath then no fusing can happen in that spot.

trident maple bonsai approach grafting

Image caption. Test fitting the scion and the trunk to be grafted onto.

  • Bring the scion to the rootstock and line up the cambium of both as best as possible.
  • Repeat this for the number of scion's you have.

trident maple bonsai approach grafting

Image caption. The almost finished "assembly"

  • Using your cable ties you can tighten them around the scions and rootstock. There should ideally be no gaps between them.
  • Seal along all the sides with your sealer.
  • Place in your container and continue with the rest of the process as a normal repotting. 
  • Water thoroughly to get the growing media to settle and to remove any dust or fines. (If you chose to use a water based sealer, at this time it will wash away so sealing after watering would be advisable - obviously)

Whenever repotting bonsai trees, please ensure that you wire the tree into the container. This is to prevent it from being blown out the container as a worst case scenario but at minimum it prevents the tender new roots from being broken by vibrations caused through movement from wind.

Aftercare

There is nothing different about the aftercare for this planting than any other newly repotted tree. Essentially keep it out of strong winds.

Watering will be reduced as you have removed roots and thus the plants ability to absorb moisture will be retarded. Be sure to water with either a watering can or wand  which has a fine spray to avoid eroding your growing medium.

trident maple bonsai approach grafting

Image caption. Do not feed at least for the first couple weeks until you see that the tree has recovered from the repotting.

When you begin feeding do so lightly. Use a slow release, organic fertilizer which does not have a high concentrations of Nitrogen. As the trees strength increases you can gradually increase the amount of fertilizer or frequency.

Next Steps

Allow the scions to grow unclipped for the entire growing season. The more they grow the quicker the fusing of the scion and rootstock will be.

trident maple bonsai approach grafting

Image caption. If you see that the scions are fusing and growth is strong then you may need to remove the cable ties to prevent cutting in. Be sure of this though because with species such as the Trident maple if fusing has not taken place properly the scion might actually pop off. So as a safety precaution you might simply want to put new cable ties on.

trident maple bonsai approach grafting

Image caption. Above is a close-up of the callousing happening between the scion and the rootstock.

You can now repeat this process in spring as many times around the trunk as needed to create the desired taper you want.

Final comments

When the "trunks" of the scions have done their job then you can shorten them. Use a concave branch or knob cutter to perform the final cut so that when the wound heals it will not be noticeable. In this instance I would advise the use of the putty type of sealer rather than the thinner Kiyonal paste.

trident maple bonsai approach grafting

Image caption. When you are happy the scions have completely fused you can cut them and seal the ends with a putty type sealer to promote callousing.

I have noticed that it is best, for aesthetic reasons, when performing the grafts to do so in such a way that the scions will fuse at different heights to avoid a sort of ring from forming.

After doing the initial grafts of both sides and the front and back, you can now fill in the gaps between them.

This technique not only accomplishes the goal of creating taper in an otherwise uniform trunk, it also helps you achieve a better nebari.


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