The right time:
Regular repotting is very important for the health and development of a bonsai. As a rule, deciduous trees should be repotted every two years and conifers every 3-5 years. However, depending on the plant species and the state of development should be decided here individually. Repotting too early weakens the plant, as it usually takes root in the first year and does not sprout normally until the following year. Too late repotting, on the other hand, results in a lack of space for the roots in the tray and branches may suffer or even die due to the undersupply of water and nutrients.
At the same time, however, a certain lack of space in the pot leads to short shoots and the desired maturation of a bonsai. Finding the right time to repot is therefore a matter of degrees, and it is advisable to document the repotting cycles and keep a close eye on plant growth. However, if the soil surface is very hard and the plant hardly absorbs water when watered, this is a sure sign of a compacted root ball. Also, the drainage holes at the bottom of the pot are then usually overgrown. Repotting should be done at this point at the latest. Deciduous trees are ideally repotted in the spring (February-March) before leaf emergence. For conifers, late summer (September) may also be recommended, depending on weather and overwintering possibilities. Indoor bonsai can be repotted throughout the growing season (February-October).
Potting out:
Prior to potting, the work area should be prepared with all necessary tools and utensils to allow for speedy and effective work. First, remove the wire around the root ball. Then, using a special knife or an appropriate root saw, the tree can be easily detached from the pot. Especially with heavily rooted species and bulbous pots, the saw is often the only way to get the tree out. In the worst case, the pot must be split with a hammer.
Root pruning:
Just as with the crown of the tree, emphasis should be placed on a good root system structure. When repotting, the roots are first untangled with a root claw. This is done by working from the trunk outward without tearing the roots. The loosely hanging roots can then be shortened with sharp scissors. Thicker roots can also be cut with pliers. Heavy cuts are then best treated with a special root paste.
Root base:
For a beautiful root base, it is also important to encourage the lateral roots and not the lower roots. For this purpose, the bottom of the root ball is shortened more. However, there should always be enough fine roots left on the tree to ensure that the plant will grow. The root base should then be cleaned with a brush and water before potting. Visually disturbing roots can now also be removed completely, if the tree can physiologically do without them.
Preparation of the pot:
If the tree has outgrown its pot, a new one can now be selected. Size is critical here for healthy growth. Too small pots will quickly lead to deficiency symptoms and too large ones will promote waterlogging and thus also endanger the health of the tree. If the old pot is used again, it should be thoroughly cleaned. The first thing to do is to cover the drainage holes with a net so that the soil is not washed out. The nets must be fixed with a wire. By the way, by using colored nets, you can easily determine the time of repotting. Most often, the pot also has special wire holes to fix the bonsai. If these are not present, simply use the drainage holes.
Substrate:
Special bonsai substrate (e.g. TerraSai) is then poured into the finished prepared pot. It should be a structurally stable mixture adapted to the plant species and developmental stage. Only enough substrate is poured in so that the tree subsequently has the appropriate height in the pot. The root base should be neither below nor above the edge of the pot. Before the tree is inserted, it is recommended to use a starter fertilizer (e.g. BioGold Classic). Conifers in particular can now also be inoculated very well with a mycorrhiza fungus (e.g. Vitalin).
Wiring:
As long as the tree cannot yet hold itself in the pot by its own roots, it is essential to wire it on firmly. This prevents the plant from tipping out and the fresh root hairs can grow undisturbed. To do this, the wire is passed over the root ball, tightened and twisted. The superfluous wire is shortened. If the wire runs over the root base, some protective tubing can be used here. After wiring, the tree should sit firmly in the pot and be able to be lifted up by the trunk without any problem.
Potting:
After fixing the tree, fill in the remaining substrate and work it conscientiously into all the cavities with a chopstick. Care should be taken, however, that this does not cause the roots to rise to the surface and then protrude from the substrate.
Watering:
Once the plant has finished potting, it must be watered thoroughly. Watering should be done until the water runs out of the drainage holes. The substrate should also not dry out from now on, but waterlogging should also be avoided. Some sensitive species with particularly shallow pots will benefit from a thin layer of fine Sphagnum moss sprinkled on the soil surface during this time.
Aftercare:
Frisch umgetopfte Bonsai sind empfindlich und sollten hell und geschützt vor Frost, Hitze und Wind stehen. Sobald die Pflanze austreibt muss auch auf einen Schädlingsbefall geachtet werden. Läuse befallen gerne den Neuaustrieb und müssen umgehend entfernt werden. Sobald die Pflanze angewurzelt ist und kräftig treibt, kann mit dem Düngen begonnen werden (ca. 4-6 Wochen nach dem Umtopfen).