Tree Tips
January 2025
This year, Juan Cruz will devote the first program to transplanting. This is a vital activity that jump-starts the bonsai year. He will approach transplanting from his vast experience working at a bonsai nursery in Japan, which may vary slightly from my own experience here and in Japan. I’m looking forward to learning something new or a clearer way of expressing the process. There’s always something fresh that I can learn.
But first, my take: think about setting up for transplanting. Gather the soils, tools, wires, and pots you will need. Then renew the screening and tie-down wiring of the pot. Consider the new front you want even before you start actually repotting.
Below is my yearly transplanting regimen, which will give you a head start on the process.
Repotting
Each time we transplant, it gives us another opportunity to improve our tree’s nebari and accelerate the growth and development of our trees.
We want healthy and vigorous radial root systems for our trees, and we all know that if we accomplish this, we will have better bonsai. The root system affects everything above it. Repotting our tree accomplishes many things: it rejuvenates the tree by freshening the soil, increases the amount of oxygen available to the tree, initiates the taper of the trunk for which we all strive, corrects problems in the root system, and may solve problems in the upper tree. By cutting back the roots, it encourages the tree to generate new absorbing root tips closer to the trunk, making a more efficient plumbing system and allowing us to place the tree into a shallower and more appropriate pot. So, let’s get to it.
We in the Bay Area are very fortunate with our mild climate. The winter solstice (December 21) gives us the smallest amount of daylight in the year, but the days get longer until it reverses at the summer solstice. So, the race is on! Don’t wait for the buds to swell on the deciduous trees to begin repotting your trees—start now.
One caveat before we start: we do not completely bare-root conifers. Doing so might damage or kill the tree! We do need to get the field soil out of the mix, but not necessarily all at once. Removing all the soil from a third or halfway around the trunk will ensure enough undisturbed roots remain to keep the tree alive while the bare-rooted section builds up a new, healthy set of roots. Two years down the line, you can clean out the other part while leaving the new roots intact to maintain the tree.
REMOVE TREE FROM POT
If in a bonsai pot, cut tie-down wires from beneath the pot and loosen screen clips from the drainage holes. If the tree does not come easily from the pot, use a sickle or knife to cut a wedge (higher at the surface) between the roots and pot along two short sides and one long side of the pot. From the cut long side of the pot, hold it down with one hand while your other hand pushes the upper trunk up to release the root ball. Don’t grab the trunk where valuable bark can flake or rub off; hold a jin or sturdy upper branch. Take your time and do it right. Lift the tree and root ball from the pot and set it aside in the shade while you clean and prepare the pot. If using a different pot, prepare it before removing the tree from its original container.
PREPARE THE POT
Clean off the grime with natural fiber brushes and a good water scrubbing. I also apply mineral oil to the pot to slowly dissolve the mineral deposits on the rims, feet, and bottom edge. Then, put screens in the drainage holes and wires through the holes for tying the tree down later. If there are two holes in the pot, put two wires in each hole. If you have four holes, use two wires, with one end through each hole. We’ll discuss what to do with them later.
PREPARE THE SOIL
Premix your soil components into a large batch so you don’t have to scramble later. Have sufficient larger-sized pumice or decomposed granite for a bottom drainage layer. Don’t worry about stratifying water in the layers; when you put a tree in the pot, it alters the layers and creates a different dynamic for drainage. I have good success using more of the imported clay material, akadama. Japanese pumice, called hyuga, is another additive I like, but domestic pumice would be just fine. The clay (akadama) should hold nutrients in the soil better, and the hyuga should lighten the mix and improve drainage. Here is a basic, fast-draining conifer mix: 1 or 2 parts akadama; 1 part pumice (hyuga); 1 part brown lava or decomposed granite. For deciduous and broadleaf evergreens, you might add 2 to 4 parts akadama, depending on how much water retention you want or if you want slower, finer growth. For every 5-gallon bucket, add in ½ cup charcoal and ½ cup super phosphate to the mix. The size of soil used for your tree will depend on its stage in the bonsai process. Freshly collected and nursery container transplants will need coarser (larger) sized particles. Sickly or weak trees should have this coarser soil as well. Medium/large akadama would work well here. For developed trees, I use a smaller-sized mix of akadama, pumice, and lava. This will create finer roots and top growth. For top dressing, I use a slightly smaller, sifted mix of this smaller soil. Even if you don’t start transplanting right away, assemble the soil components you need now.
If you don’t have bonsai soils or access to akadama, Drew Tucker (831-402-6845) in our club will have soil, tools, and wire to meet your needs. Jonas Dupuich has a fine article on his Friday, December 17th, 2021 Bonsai Tonight blog titled What to Do When Akadama Is in Short Supply. Check it out for some helpful suggestions.
PREPARE THE TREE
Transplanting should be done when the soil is damp but not soaked. It is a little messier than when dry, but the roots will not dry out as quickly if they are moist. After all, healthy trees are our primary concern. (Of course, the new soil we will be adding will be dry, as it’s easier to work into the roots.)
When you have it out, gently scrape off the thin layer of surface soil around the tree, exposing just the upper surface roots. Remove the hold-down wires from the top of the soil surface if you can, pulling away from the trunk, not straight up.
Tilt the tree to the side 90º, holding the root pad with one hand. Using a small rake, loosen then cut out the layer of matted bottom roots, keeping the root mass an even thickness over the entire surface. Comb out the roots in this area, removing large roots with root cutters and those smaller roots growing directly down from under the trunk of the tree with bonsai shears. The underside should be flat or like a slightly inverted saucer. Clean out any dead roots or rotted wood you encounter. When you have cleaned out the bottom surface, return the tree to its upright position.
Using bent-end tweezers or chopsticks, gently tease the surface roots from the trunk to the edge in a radial direction. If there is old field soil remaining, dig it out. If you encounter crossing roots, straighten them out. Most healthy deciduous trees can be bare-rooted if there is field soil present, but if it has a good draining root ball, it does not all have to be removed. Again, conifers should not be as aggressively combed out. If you have a lot of old soil that needs to be removed on a conifer, clean out just one side this year and leave the other side intact. In two years, you can clean out the other side to complete the process.
Once you have the roots combed out, cut the roots so that you have about the same amount in the front and rear. Allow some root tips to extend past the root ball so that they will move easily into the new soil you will put them in. REMEMBER: this is where the new absorbing root tips will form, so give them enough room to grow and make sure to make clean cuts.
For reduction of nursery containers, first scrape away soil from the base of the tree until you have a good set of surface roots. Saw or cut off from the bottom at least one-third to half of the remaining root mass. Tease out the roots as above, encouraging radial side growth rather than downward ones. Make clean cuts at all times. We will reduce the soil ball further next year.
We usually don’t put trees from nursery containers directly into thin bonsai pots. For the health of the tree, choose a transitional deeper intermediate-sized container for the first transplant. Anderson flats make a good transitional pot. Again, this is not a race!
REPOT THE TREE
Put a thin, flat drainage layer of larger particle soil in the bottom of your prepared pot. Place a mound of soil (like the above-described inverted saucer) where the base of the tree will rest. Place your tree so that the front of the tree and the tree angle are correct. The soil level should be slightly below the pot rim, and the buttress of the trunk should start at the level of the pot and not high above it on a mound. If you can, have someone hold it in position for you and step away to make sure it’s at the proper angle. Get it right now, or you will have to live with it until the next transplant. Add soil around the edges of the root mass and work it in with chopsticks. Don’t just dump it in on top of the roots—let it sift through the roots so they are separated and not matted. Chopsticks can be used to help the dry soil filter around the roots. Stick the chopsticks into an area where you need soil, and then work them in a back-and-forth manner to direct the soil where it is needed. Don’t just jab the chopsticks in and out, or you can tear and damage the roots. Make sure that soil has penetrated into all areas. We don’t want any air pockets.
TIE DOWN
If you have four holes in the bottom of the pot, use the wire tie-downs in a clockwise or counterclockwise fashion to secure the tree in the pot, tightening them by twisting and pulling with your fingers at each wire intersection. The final wire is tightened with wire pliers to pull the whole basket weave together and cinch it into place. Add more soil and work it in well with chopsticks. While holding the root mass down with one hand, gently bang down on the rim of the pot with your other hand all the way around the pot. This will settle the soil into cavities you missed with your chopsticks. Use a small brush to sweep the surface of the soil flat, then tamp down with a small spatula. If you have only two holes on the bottom of the pot, after you have worked the soil into the root area, lay chopsticks down across the root area on either side of the tree, and then tighten the back two wires over the chopsticks and then the front wires. This will help hold down the tree and give added stability, even when there is a marginal root system. Sprinkle some shredded sphagnum moss on the surface of deciduous trees.
AFTER CARE
Gently water in well from overhead until the water runs clear from the bottom of the pot. Keep the soil moist, but don’t let it get too wet, or you can develop root rot. It can’t process as much water as an established tree until it forms new absorbing root tips. Protect the tree from drying winds, frosts, and excessive sun. To be doubly safe, you might use something like Cloud Cover, which is an anti-transpirant.
If we have a burst of freezing cold, the transplanted trees and others that have young, tender shoots will need to be protected from damage. However, this should not deter us from transplanting everything we can get our hands on, starting with fruiting, flowering, and other deciduous trees, followed by the evergreens. To give it an extra boost, or if you have excessive cold after transplanting, you might use a heating mat under the plant. This bottom heat will stimulate the roots without the extra stress of supporting top growth. Don’t fertilize until you see strong new growth.
If you are pruning and styling your trees, remember that the closer we get to the growing season, the closer you can cut back to the last bud. If you still think there might be frosts, leave a little stub at the end. You can trim it later in the year.
This is also a time to apply dormant sprays to head off problems. Bordeaux mixture is a dormant spray that has been around for years. Lime sulfur spray may be used but is difficult to come by in California, as it was pulled many years ago. Oils can be used on deciduous trees, but keep away from junipers and some other conifers. In the early spring, you can put down some Cleary’s 3336 granules as a fungicide and some Merit granules to target insects. Both of these (big bags) I got at Sierra Pacific Turf, 510 Salmar in Campbell.
It may be pretty chilly at night. Remember to protect all tropical and semi-tropical trees and any recently transplanted trees if there is a chance of frost or freeze. Non-transplanted temperate trees can handle the cold, but newly transplanted ones are more tender. Take them inside your garage or dangle an incandescent lightbulb near them at night to warm them up. 🌳
