Updated: Jan 7
Something i have seen a lot of lately is people asking questions on repotting but they are talking about something completely different and getting the wrong advice for the wrong techniques. Today we will take a look at Repotting, Slip Potting and Potting a developing tree into a Bonsai pot for the first time.
So as mentioned about these are 3 different techniques that all get called Repotting. If you were to look at it in very simple terms then i can understand that the tree is technically getting repotted even if it is just a slip pot from one growing container to another. But all 3 are very different from each other and require different techniques and levels of care during the process and aftercare.
REPOTTING - Lets start with the classic Repotting. When we Repot a Bonsai we are taking a tree that has been in a Bonsai Container for roughly 2 years for Deciduous / Evergreens and Aus Natives or around 5 years for a conifer and trimming the roots back slightly to allow the tree more room to grow in the pot as it becomes root bound. If we don't do this process the roots will eventually fill the pot and stop growing, if our roots stop growing then the tree stops growing so you will see a decline in the health of your tree until it dies if not done. We usually only Repot for 3 reasons 1. loss of percolation ( tree is not taking on water because the pot it full of roots )
2. Change of design / Angle or Pot.
3. Soil has broken down.
Some people repot on a schedule un aware of why they are doing the repotting. It is a fine balance between letting the roots fill the pot which restricts growth giving us smaller everything but not letting it get so restricted that it becomes un healthy. Some people repot way to early while others don't repot at all. Understanding why we do it though helps us with our timing. When repotting we usually take the entire bottom matt of roots of and tease the compacted soil from all sides of the tree, we then proceed to trim back the roots we teased out with very sharp scissors, the sharper the scissors the better the root will callus and begin to grow new roots from the cut site. This is why cheap tools create poor trees. Once we have done that we can then get some new fresh soil in the pot and repot the tree, we need to be sure to chopstick through the new soil to remove and large pockets of air as roots wont occupy this space. When repotting we only remove a small amount of roots and its more or less a maintenance task that is a very important one at that. After repotting i usually keep the trees foliage wet when watering to slow transpiration for around 2 weeks while the tree recovers, if the weather gets very hot very quick i will proceed to protect the tree with shade.
If you think about it the tree now has a semi functional root system which is how it takes up water, if the tree is exposed to a lot of wind or heat and cant keep up with the demand of water to the foliage it will suffer.
SLIP POTTING - This one is very simple and wont take long, slip potting is basically taking a developing tree in a growing container and moving it into the next size up container, so from a 8" to a 10" for example. We can do this anytime of year as we don't really disturb the roots when we do it, The trick is to slip pot the tree when it has got enough roots to fill the soil in the pot but not so many roots that they are growing in circles around the pot. If you catch it just before you can simply take it from the smaller pot to the larger pot and put new soil around it and the tree wont skip a beat. If your tree is root bound then you'll need to tease the roots out a little to free them up and then do the same process by putting it in the larger pot with new soil around it. In the case of a root bound tree there will be a lag in the time the tree begins to grow again due to it slowing down because it was root bound. While slip potting this is a great time to change the angle of the tree if you need too. Once this process is done the tree can go back to its normal spot on the bench and continue on as if nothing happened.
POTTING FROM DEVELOPMENT TO A BONSAI POT - Ok so this is when we take a tree from the development stage of growing the tree in growing containers to putting it in a Bonsai Pot with a new type of soil ( usually in organic soil such as Akadama ). This can be a stressful time on the tree, more so then actually just repotting a tree. On the lead up to doing this we need to make sure the tree is bursting with energy and is very healthy and hasn't just had any major work done to it. Moving from a nursery container which is fairly larger and deep to a small Bonsai Pot that is shallow means taking off a lot of root mass, Deciduous can lose up to 70% of its root mass in this process and conifers and evergreens lose around 30 - 50%. In this process our goal is to also remove any tap roots, Thick Roots or roots that are growing downwards. We want to keep fine feeder roots and laterally growing roots. Once we have our reduction done in our root mass we need to have the pot properly prepared with drainage mesh, Tie down wires for the tree and a drainage layer of larger particle size soil on the bottom of the pot. When potting up a tree we need to make sure the tree is tied down well as the tree wont be able to support it self with the root system being so small now and the very loose soil system, if you don't tie the tree into the pot properly the tree will move in the wind and tear any new roots that have grown so this is paramount!. You also need to make sure you chopstick all your new soil in through the root system properly to make sure there is not air pockets. Aftercare for this will require the tree to be protected for around 2 weeks while it recovers its roots system. Make sure the tree isn't exposed to high winds or high temperatures. Keep an eye on your watering and adjust accordingly.
Ok so i know i gave some instructions on what to do in each of those different potting scenarios but they are not in depth tutorials on what to do, we will need to dig deeper for a proper lesson on each, my brief descriptions above were more or less so you could understand the difference in goals and work carried out for each, this will help you recognise what you are actually doing. At least you will now know that Repotting is 1 technique and there are actually different methods for the others.
Until Next Time, Enjoy Your Bonsai Journey.