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For the Beginner Part II

Basics of potting

By Victoria Petermann

Although it is the beginning of winter it is amazing how fast spring and the potting season arrive. When it does, you want to be prepared so as to be able to manage potting all the trees that need to have a change of soil.

Now is a good time to mix your potting soil. What goes into it will depend firstly on the different growing conditions experienced in the area where your trees are grown. Amount of rainfall or wind exposure, for example are some of the factors to take into account when you mix your soil. Your second consideration should take into account the different growing needs of the different trees. Newly developed bonsai need a soil mixture which will encourage maximum amount of growth as opposed to well established bonsai which need to be maintained within their developed shape. Different species of trees also have different requirements for best growth, for example, azaleas like to grow in an acid soil mix; olives like to have a well draining mix as they dislike being waterlogged.

The most popular mix consists of 3 parts coarse sand (essential for good drainage), 2 parts loam (a mixture of clay, humus and sand useful for retaining nutrients and trace elements) and 1 part leaf-mould (for its excellent water retention capacity). These three components are dried and sieved into particles of sizes ranging from l.5mm to 6mm. Anything bigger or smaller is discarded. These elements are then mixed altering their proportions to suit the growing needs of each particular tree. To allow the soil to get between the root spaces with ease when potting, it is preferable to use your soil mix dry.

The sap will start moving in some of your tree as the end of winter approaches. When the buds start swelling it is the best time to pot the plant Before you start disturbing the roots, make sure you do whatever pruning and wiring which is necessary on the top of the tree as doing this to a newly potted plant will greatly damage the root system.

For potting you will need soil mix, pots, rod or spike (to loosen the old soil and comb out the roots), cutters (like scissors, secateurs etc.), fly-screen mesh cut into small squares, a basin filled with water, a chopstick and at times a water hosepipe nearby can be useful to help dislodge the old soil. Assure yourself that everything you are going to need is next to you before you start potting.

If this is the first potting of the plant ie. it is coming out of a nursery bag, then you will find a solid looking block of soil when you remove the bag. (Fig.1)

Figure1Figure 1

First loosen the soil a little with the rod or spike and start removing it slowly from the sides and the bottom. (Fig.2)

Figure2Figure 2

It will depend on the species of the plant how much soil to remove in the first potting. With deciduous tree it is ususally safe to remove all the soil and even to wash the rootball with a hosepipe. (Fig.3)

Figure3Figure 3

With needle trees (such as junipers and pines) and with azaleas it is better to leave some soil around the roots which can slowly be removed a little at a time in subsequent repottings. (See Fig.2)

Without the soil you can inspect the rootball and decide which thick roots you are going to cut off and which you are going to keep. (Fig. 4)

Figure4Figure 4

Try to retain as much of the hair roots as possible and remember to maintain a balance between the amount of foliage which you've pruned off the top of the tree and the amount of roots which you remove during potting. Make sure that the pruning shears are sharp so that they do not leave torn, squashed edges as these could lead to root-rot or the cuts not healing readily. Do not let the roots dry out when working on them and if you need to leave the plant unattended with exposed roots for a while, make sure that you place the plant in a basin filled with water.

Cover the drainage holes in the bottom of the bonsai container with the fly-screen mesh (Fig.5) and put a thin layer of soil mix in the pot.

Figure5Figure 5

Then place the tree in the appropriate position in the pot, usually towards the back and to one side and then cover the roots with more soil. Holding the tree with one hand gently work the mix in between the roots with the help of a chopstick. Make sure that soil also gets underneath the trunk base and that you do not leave too many air pockets between the roots. Finish off by soaking the potted plant in a basin of water for a few minutes, until the bubbles stop rising.

If the plant to be potted has already been established in a bonsai pot for some time, then the potting procedure is slightly different. Take the tree gently out of the pot and remove the about 2/3 of the soil from the sides and about 1/2 from the bottom. (Fig. 6). Comb the roots out and then trim about 1/3 of the roots all around (Fig. 7). Then follow the same steps as with a first time potting.

Figure6Figure 6

Figure7Figure 7

It is important to give special attention to the after care of a newly potted tree. For about four weeks place the tree in a sheltered position away from direct sunlight and wind. Keep the soil moist and try to spray the foliage of the plant a couple of times a day.

As mentioned earlier, the best way to tell when a tree is ready for potting, is to watch out for the swelling of the buds. Deciduous trees are usually potted earlier than evergreens. Usually the first species ready to be done are Taxodium followed by Celtis (July/August). Zelkovas and maples follow around August/September. Pines and junipers like to be done when the weather is slightly warmer (September/October) and figs when it is much warmer (usually around December/January). Azaleas and many of the flowering plants are potted as soon as the flowering period is over. Indigenous trees such as olives and Buddlejas have a couple of growing periods in a year and they are potted when the tree is growing strongly.

Not all your bonsai will need to be repotted every year. The smaller ones, mame and shito, do need to be repotted yearly but the rest will grow happily in the same soil for 2 or 3 years, provided that they are watered and fertilised regularly so as to maintain the health of the plant. Enjoy the potting season, it is then that you get to know your trees.

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Haiku

Grey marsh, black cloud...

Flapping away in autumn rain

Last old slow heron. ~ Anon

Random Bonsai Tip

Collecting moss - During winter, check your roof gutters for moss - usually a very fine bright green at that time of the year.