The Idiots guide to repotting
As a bonsai enthusiast of limited years. I can sympathise with novices when the prospect of repotting trees looms imminently on the horizon. This is an absolutely essential operation to keep the trees in good health and growing strongly. Trees that are pot bound have poor drainage, inadequate aeration, and a quickly deteriorating root system, that eventually leads to decay, root rot and finally death. (Get the picture? Best get the good news over first).
Lots of books and (bonsai experts) have differing theories on when the tree needs repotting, I have always found the best way is to take the tree out of the pot and look at the roots. If you can see little else but roots and the compost seems to have magically disappeared, then it definitely needs repotting.
Before you start you need to make sure you have everything you need, there is nothing worse than chasing around looking for a new pot, leaving the roots of your tree to dry out in our glorious winter sunshine. (Check that you have the following)
- Somewhere dry to work, this could take longer than you think
- A Root hook, Chopsticks, Knitting needles or similar device for teasing out the soil.
- A spray bottle filled with water to keep the roots of the tree moist.
- A new pot, or the old one thoroughly washed and sterilised ( I use “Milton’s”)
- Some plastic mesh and wire to block the holes in the pot.
- Some natural fibre string or wire to hold the tree in the pot ( I prefer natural string as it rots away between pottings)
- An adequate supply of compost prepared in advance
- A watering can with a fine rose sprinkler or spray bottle
Bonsai soil
Lots of information written on this, all it did was confuse me, I have now settled on a mixture of Akadama and Kyodama with some composted bark to provide the organic content. (Also helps in the transition between soil and soiless compost) Akadama and Kyodama are perfectly good on their own but we all like to add our own individual ingredients. I used to use cat litter but have moved away from that now. Don’t forget to add trace elements to the mix as these are essential to the trees well being. (This compost should be prepared in advance, make sure you sieve it first, and allowed to stand prior to use, I usually mix it a week in advance and store it in dry, airtight containers).
Getting stuck in
1 Hold the tree by the base of the trunk and ease it out of the pot. If the compost falls away in lumps and the tree has been in the pot for more than a year put it back in the pot without disturbing the roots and immediately investigate.
Removing the old soil
(The golden rule is “Be Gentle”). Start at the bottom edge, untangle the coiled roots and then work your way up the side of the root mass combing out uniformly all round. When you get to the top edge work your way to the trunk. Finally you need to attend to the underside, remove proportionally as much soil from here as you did from the side. The higher you can get into the centre the better. By the time you have finished you should have removed half to two thirds of the total volume of soil.
Cutting the roots.
YOU MUST USE CLEAN, SHARP SCISSORS TO DO THIS This is the delicate part of the job, the idea is to cut off the straggly roots so the tree will fit back in the pot with enough space around to accommodate a good supply of fresh soil. With small bonsai 15mm should do. Leave more space with larger trees. It’s not quite this simple and I would advise you to seek help from one of the training officers if you don’t feel confident.
Preparing the pot.
Clean and sterilise the pot beforehand, you will need to fix some plastic mesh over the holes securing it with a small length of wire (Any bonsai book will show you how). Traditionally wire is pushed up through the small wire holes in some pots (You have a different challenge if your pot lacks wiring holes, but don’t despair it can be solved) I prefer to use natural string instead of wire whenever I can for the following reasons.
1With time wire can cut into the roots, particularly if the repotting schedule is every 3-4 years
2. String will decay by the end of the first summer, so the roots are free of danger
3 By the time the string has decayed the tree will have grown sufficient roots to hold it in the pot
Re planting the tree.
#Make a small mound of compost just off centre of the pot; this should be directly beneath where the trunk will sit. Spread out the roots to form an attractive “Nebari “, position the tree and settle it down in the pot by gently twisting it from side to side until it sits securely on the mound of soil you placed in the pot.
Things to check
1 are the front of the tree and the front of the pot facing the same way?
2 Most trees look better placed slightly to one side of the pot and slightlytowards the back of the pot
3. Check the tree is at the correct angle both from the front and the side
(I have made simple jigs with sticks and string to hold trees in place whilst repotting. I have to say an extra pair of hands is sometimes better). When you are happy with all of this bring the wire or string over the roots and fasten securely. Try not to cut into any roots with either as it will only get worse with time ( I often place a small piece of tubing over any roots that look likely to get damaged) Have a final check to ensure the tree has not moved while you have been fastening it in place
Replacing the soil. This is where you will need you chopsticks again. Add soil around and over the roots a handful at a time, as you add the soil work it between the roots with the chopstick. Insert the chopstick between the roots and move in a circular motion allowing the dry compost to fill in the spaces between the roots. (We don’t want any air spaces left) DON’T STAB AT IT WITH THE CHOPSTICK.
When you are happy there are no air spaces you are nearly finished, all you need to do is water your bonsai. You need to do this very gently as you have removed a lot of the trees roots, so the compost will easily wash away (Use a spray or very fine watering can). Water until compost is saturated and then repeat 10 MINS later. You should now have a potential Best of British show winner
Aftercare. You must now keep your freshly potted bonsai out of the frost (SHED OR GREENHOUSE, NOT INDOORS). Water only when dry and then around the edges of the pot (This encourages new roots to go looking for water). DO NOT feed for about six weeks after repotting as this actually retards root generation.
These article gives you the major points of repotting and if followed your tree will flourish. However Coniferous, Deciduous and flowering trees all have particular needs and the compost used the time of year for repotting can vary slightly. It is worth checking these details with a club officer before starting.
Dave Y February 2009