Repotting bonsai
First planting in a bonsai pot
Moving a plant from a large container or from the ground into a bonsai pot for the first time may not seem all that difficult, but we are dealing with a miniature plant in which every small detail matters enormously. Before repotting, we need to choose a suitable pot and know how much of the roots we will have to cut back so that the young plant sits in the pot exactly as we intended. Very often, when planting into a bonsai pot for the first time, things don’t turn out exactly as planned. You may not manage to cut back enough roots to fit the plant into the pot, or you may realize that getting a beautiful bonsai calls for serious changes to the plant’s shape and size. Be ready for all of this, and try to find the best way out of whatever situation arises. To start repotting, get ready a suitable pot, enough soil, your tools and the other materials you’ll need. First of all, so that the soil doesn’t wash out during watering, the pot’s drainage holes must be covered with fine metal or plastic mesh. To keep the mesh from shifting while you fill the pot with soil, fix it in place with wire.
After repotting, until the plant has rooted in well, the bonsai must be firmly anchored in the pot. To do this, thread wire up through the drainage holes from below; we will use it to tie in the freshly repotted plant. This wire is only temporary; once the plant has rooted in well, it should be removed. If the pot has only one drainage hole, or you think you won’t be able to bring the wire through the drainage holes to where you need it, it’s better to make extra small holes in the pot for the tie-in wire. After that, we spread a 1–1.5 cm layer of fine gravel on the bottom of the pot to improve drainage, and only then the first layer of soil.
The next step: we choose the spot in the pot where the plant will go. In rectangular and oval pots, the tree is planted at the point where one-third of the pot’s length crosses one-half of its width. In the case of the Shakan style, the lean should point toward the two-thirds side of the pot. In the Chokkan and Moyogi styles, the lowest, longest branch should extend over the two-thirds portion of the pot’s length.
In round, polygonal and square pots, the plant is placed in the center. A bonsai is also planted in the center of a tall pot, in the case of the Han-kengai and Kengai styles
When you plan a repotting, be sure to take into account how moist the soil the plant is growing in is. Very wet soil is a problem, because it makes it quite hard to remove the excess soil from the roots. So try not to water the plant for a few days before repotting. Repotting is normally done during dormancy, and the plant will come to no harm if you don’t water it for a few days.
How to take a plant out of a large container: first, cut off the roots that have grown out beyond the root ball. Then start removing the soil. Use a root rake and a pointed stick for this. Push the pointed stick down into the soil from above in different spots. This gradually loosens the soil and makes it easier to remove it from the roots.
Work out carefully what size of root ball the plant should keep so that it will fit into the pot you have chosen. Make sure that after removing the excess soil and pruning the roots, there will be enough room in the pot for fresh soil. You may not get this right on the first try. So once you have removed a certain amount of soil and roots, set the plant in the pot, look carefully, and decide how much more soil and root needs to come off for the plant to “fit” the pot exactly as you intend. You may need several more tries to get this right.
The soil must be removed very carefully. The fine roots that supply the plant with nutrients are easily damaged. It’s true that some roots have to be cut back before planting in the pot, but by being careless or hasty we can damage roots that the future bonsai needs. Once the soil has been removed, we shorten the remaining roots so that they stick out only a few millimeters beyond the root ball. When cutting thick roots, use well-sharpened scissors, because the cut must be clean. Be sure to cut off all damaged roots. A thick root should be cut so that the cut faces downward. That way new fine roots will grow better from the cut. Once enough roots have been pruned, we start placing the plant in the pot. Where the plant is to go, we heap the soil into a small mound. We set the plant on top and press it down gently with a half-turning motion this way and that, so that the mounded soil spreads evenly under the roots. Then we wrap the wire threaded through the holes around the trunk or one of the large roots and tie the plant in firmly.
Attention should also be paid to the planting depth in the pot. The plant should be planted neither too deep nor so high that the surface roots sit well above the rim of the pot.
Then we begin filling the empty space in the pot with soil. So that no air pockets are left under the root ball, the soil around the root ball must be worked in well with a pointed stick. This is needed so that no voids remain between the roots, which could later cause some of the roots to rot.
For various reasons, it sometimes becomes necessary to free the roots of soil completely when repotting. To make removing all the soil easier, the roots can be washed with a jet of water. The pot is prepared (gravel, mesh, wire for anchoring over the drainage holes, first layer of soil) in the same way as for a plant that keeps its root ball. After shortening the roots to the desired size, carefully separate the tangled roots, spread them out in all directions and set the plant in the pot in the right spot. Tie the young tree in with wire and fill the pot with soil. Once the pot is completely full, we take the pointed stick and carefully, slowly work it in above and around the roots.
On conifers, removing all the soil from the roots and washing them with a jet of water is generally not done; it can kill the plant. When you have finished everything, the plant must be watered. To do this, place it in a vessel larger and deeper than the pot and pour in enough water to cover the surface of the pot. Air bubbles will start rising to the surface of the water. After 2–3 minutes the bubbles will stop. This shows that the soil in the pot is completely soaked. Take the plant out of the water and put it in a place sheltered from wind and sun. Never pack down the soil after watering.
If the freshly repotted plant is fairly large and heavy, take a watering can with a fine rose and water the plant generously. When repotting, pay close attention to root pruning. It is very important to keep a balance between the amount of roots and the canopy. Don’t try to reduce the roots just because the plant won’t fit into the pot you have chosen. Cutting off too many roots can leave the plant unable to get enough nutrients. Particular care is needed when repotting conifers. Compared with deciduous trees, conifers tolerate heavy root pruning less well. It is generally accepted that when repotting a conifer you should remove only 1/3 of its root mass. But this is not some dogma that must never be broken. An experienced practitioner can tell by eye how much root can be cut in a given situation. If you have to cut back a lot of roots, try to reduce the canopy proportionally as well. You can plant an already styled tree in a bonsai pot, or plant a young tree and begin styling it after it has rooted in well and stands firmly.
Repotting from pot to pot
After a certain time a bonsai needs repotting again. Several factors make this necessary:
- the soil is exhausted and no longer holds enough nutrients;
- the plant has grown so many roots that there is no longer enough room for them to develop;
- the bonsai has grown, and its shape and dimensions no longer suit the size of the pot.
In the first two cases, if the size of the plant allows, the bonsai can be replanted in the same pot after pruning the roots and replacing the soil. When a bonsai needs repotting differs from plant to plant. Conifer roots grow more slowly than those of deciduous trees. They are repotted every 3–5 years. Some deciduous trees fill their pots with roots so quickly that they must be repotted every year. In general, young trees (under 10 years old) need repotting more often than older ones.
If you notice that the bonsai has developed to the point where the pot is no longer in proportion to the tree, you need to choose a larger pot than the current one and repot the bonsai into it. Here too, how often the pot needs changing depends on the growth habits of the plant itself. Repotting from pot to pot involves exactly the same procedure as the first planting into a bonsai pot.
When to repot
Plants are repotted in late autumn or early spring, during dormancy. If you repot a bonsai in late autumn, your main concern will be protecting it from winter frost and wind. If you repot in early spring, be sure to keep it out of direct sun for a while. A week after the buds start growing, put the bonsai in the sun for a short time (1 hour). After that, increase its time in the sun every day. After a month you can put it in the spot where it will stay permanently. Most conifer species are repotted in early spring, when the new buds begin to develop.
Moss
After repotting, we need to tidy up the soil surface in the pot. The surface should be leveled and cleaned. Some practitioners like to cover it with a decorative layer, using various finely crushed stones or marble. But in my opinion, the most fitting surface for a bonsai is soil covered with moss. Moss looks quite attractive and natural in the pot, and it doesn’t stop water from reaching the soil when you water. At the same time it helps retain moisture and keeps the soil from washing off the surface, both when watering and in rainy weather. Because the soil in a pot is constantly (more or less) moist, the surface often becomes covered with moss on its own. But you can also cover it with moss “artificially.” Moss can be found in damp, shady places: it grows on the walls of buildings, on stones or on asphalt. Carefully lift the moss with the blade of a knife and remove as much of the excess soil as you can. A few minutes before using it, put the collected moss in a container and pour water over it. It’s easier to cover the surface with wet moss. Carefully lay small pieces around the plant, close together so that no gaps are left between them, pressing them down lightly. Under no circumstances cover the surface roots with moss. You can also dry the collected moss in the shade for 2–3 weeks, crumble it finely, mix in a little soil and sprinkle it in a very thin layer over the soil surface. With regular watering, the moss will “come back to life” in just 1–2 weeks.
