In December of 2016 I had the option to buy a bunch of neglected olive trees from a trader. The plants were stored in an overfull large polytunnel. Due to the damp, standing air, in combination with being tightly packed, the plants were covered from top to bottom in black mould. Furthermore, they showed signs of weevils: Many leaves had sections missing. Finally, most branches had clusters of scale on them. All in all, the plants were in a sorry state. As the trader was clearing stock in preparation of some deep frost and did not want to care for these sick olives, he sold them to me for a fraction of the regular retail price. I spent an hour or so going through his stock, and took the two plants with the aparently best nebari and movement in the trunks home with me.
First aid on pre-bonsai material
Upon arrival I trimmed the olive plants down to the tallest I would ever want these trees to be as a bonsai, making sure too always keep foliage high upon each branch. This would keep the sap flowing to the tip of the branch, allowing for survival & backbudding the next year. The rootball was visually inspected, but no weevils or larvea were found in the rootbal. Then I took the gardenhose, and carefully washed the fungus infection off of the leaves and trunks. For trunks and branches I used a toothbrush to remove most of the black coat. Next up was an inspection of the scale. All scale was manually removed from the branches. Finally, the whole tree was drenched in insecticide, and placed in a sunny spot for the rest of winter. Only in periods of frost were these trees placed inside the greenhouse. As the roots looked healthy it was decided to leave the tree in the large container with regular potting soil for winter.
Repotting pre-bonsai olive step by step
In spring I waited untill the weather was nice and warm, and the olive started to push growth. With lush green breaking through the old bark all over the tree it was clear the tree has survived winter, and time had come to repot the olive.
When to repot an olive bonsai depends on the weather. Whenever your olive pre bonsai is growing strongly, you can repot. In my climate that typically means any time after early May. As this plant was unhappy, I waited for the real summer weather and repotted in the first week of July.
Step one for repotting a pre-bonsai olive from nursery material into bonsai training pot is to check where the main roots are located. In some cases you are lucky, and the base of the tree displays an enormous swell, creating a monster Nebari. I selected these trees because they showed some surface roots, and the base of the tree showed some swelling. When I took it out of the pot, I realized a lot of fine roots were present in the upper third of the pot. As such, I decided the lower two thirds of the rootball were unneeded.
Step two for repotting a pre-bonsai olive into a bonsai training pot consisted of taking a large saw, and cutting the bottom section of the rootball. Although this will look drastic to many inexperienced in bonsai, this places very litte stress on the remaining roots. Most of them will be split by the saw, and you avoid a lot of tugging and twisting of roots. Do however take care to later clip the ends of the roots with a sharp pair of scissors.
Step three for repotting a pre-bonsai olive tree consists of carefully raking out the rootball. Working around and around, slowly all soil is worked out of the rootball, working from the outside inward. Whenever the roots are circling the rootball, take a pair of sharp scissors and cut them. Carefully manipulate twisted roots to be more or less lineairly radiating outward, without tangling with other roots. This is time consuming, so it is best to do this in the shade, on a cloudy day and mist the roots every once in a while. I find working on a fairly dry rootbal is easier than a fully wet rootball. Do this well, and you will be left with an open rootball and all roots will radiate outwards without interfering with the other roots.
Step four for preparing a nursery olive tree for a bonsai pot is the reduction of the roots. In this depicted Olive pre-bonsai two rings of main roots were present. One at the original soil line. This consisted of a limited number of roots, some of them thick. Whole sections of the nebari were devoid of roots. A few cm deeper a second crown of roots was present. As these were well-distributed, it was decided to remove all upper roots. This will cause some challenges for the taper in the trunk later on, and this will have to be dealt with with sme carving. In the end, the rootbase is not ideal for bonsai. At the bottom of the rootball, remove all heavy roots with a knob-cutter. Trim the roots to fit the container you have selected to put the tree in.
The final step to move a pre-bonsai from nursery soil to a pre-bonsai container is the planting in the training pot. For all trees I normally use the same substrate. A chemically inert lava-like substance, mixed with baked clay pellets and bark, sifted to some 2-5mm diameter. For this olive however I decided to go for courser substrate. Mainly because I had it available. The course substrates used allow free-drainage of water, avoiding roots sufficating in ever-wet substrate. I can water my trees every day without any harm done. This allows for instance for prelonged watering by an irrigation system in case of vacation, but also in case of a heat wave.
From now on, the tree has to establish itself in the container. For this, top-growth is important, as this stimulates root formation. To this end, the olive is placed in full sunlight, and watered & fertilized frequently. During the growing season young green shoots used in the main design will be wired in place. Shoots that are not needed are removed every few weeks.