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The basics of potting

by Victoria Petermann

Potting is one of the Bonsai techniques that most seems to puzzle beginners. The more books and magazines they read, the more puzzled they become as to the exact moment when to pot a specific plant. Part of the problem is that most books and magazines are written in the Northern Hemisphere for their seasons and growing conditions. Considering that our seasons in South Africa are reversed from the European and North American ones and that our weather (specially this year in the Cape) is often unpredictable, it should come as no surprise that people are often perplexed as to the right time to pot a specific plant.

The secret of knowing when the right potting time has arrived lies in watching your trees. Each plant will tell you when it is ready; that time is when the winter dormant buds begin to swell. This period varies from year to year, depending upon the weather conditions and the different species. The potting period for most plants takes place in spring. The plants that tend to be ready for potting earlier are Celtis and Swamp Cypress, which are normally done in July. Maples and pines follow and when the weather is a little warmer (early September) it is time to do the junipers. Figs on the other hand like to be potted when it is really hot around December. We should also not forget that plants indigenous to the Cape experience a surge of growth when the first winter rains arrive and that is the ideal time to pot them. So, olives and Cape May are done normally around May / June.

There are two types of potting. What we refer to as first time potting and what we term re-potting. First time potting refers to the removal of the tree from the nursery bag so as to be able to plant it in a training pot. This is the first step that the plant will take in becoming a bonsai. A lot of root removal is usually required but most of the roots that will be cut away are the thick anchor roots, which are redundant and have nothing to do with the health of a bonsai tree in its container. It is important to retain as many as possible of the small feeder roots when potting as these are the roots that absorb water and nutrients for the plant and therefore keep it healthy. This is the time to begin correcting the aesthetic problems that the root system may have. Balanced surface roots are most important to the overall look of a bonsai. A balanced root system will also result in a balanced canopy of foliage at the top of the tree; one side of the plant should not grow over vigorously to the detriment of the health on the other side of the tree.

To avoid dehydration of the plant caused by the removal of a fairly large amount of roots, it is important to remove a similar amount of top growth from the tree at the time of potting. This maintains a balance in the plant between the amount of roots that it has and the amount of leaves which it has to keep healthy.

Every time that the plant's soil is changed after this initial potting is called re-potting. Re-potting takes place every 2 to 5 years, depending upon how well established the tree is and on how much growth is required of the plant as every time the plant gets fresh soil, a vigorous growing season usually follows. Removing about two thirds of the soil from around the perimeter of the plant and about two thirds from the bottom, without disturbing the soil closer to the plant is usually sufficient in most re-pottings. Then, trim the exposed roots by about half and add fresh soil to the pot, working this in slowly between the roots with the help of a stick. It is again important to balance the amount of roots cut with the amount of foliage removed so as to stop the plant from becoming dehydrated due to a semi-functional root system.

Regardless of whether the plant has just been potted for the first time or whether this is a subsequent potting, it is important to give the tree some additional care during the period following the procedure. Ensure that the plants do not dry out and if possible mist the foliage regularly. Place them in semi-shade away from the sun and from strong wind, as both these conditions would lead to dehydration of the newly potted plants.

The type of soil used for bonsai should be good at retaining moisture while being freely draining and coarse enough to encourage healthy root growth and fine ramification. Other than that, there are as many great and favorite mixes as there are bonsai growers; as each of us believes that the soil we mix to grow our plants is the best soil of the lot. If your plants grow well in the soil that you are using, then it is the right kind of soil for the location where you grow your trees. Soil is usually easier to use when dry, as this will allow you to get it to reach in between the hair roots with ease After potting, dunk the tree in its pot for a few minutes into a container full of water to allow the soil to be thoroughly soaked.

One of the most common mistakes that beginners make when potting is to be impatient and to place their training plants too quickly into their final bonsai containers. This is not a good idea. These plants will take a lot longer to mature than the plants that are placed in big training pots The earlier the time that the size of the pot is reduced, the earlier it is that the volume of the soil is diminished and therefore, the earlier the time that the growth of the tree is restricted. Do not rush this process, keep your plants in big plastic buckets to allow for maximum growth for as long as they are developing.

Sometimes it is necessary to pot a plant out of season. This is not recommended as it is easy to lose the tree in the process but there are times when we have to make an exception. If there is a plant that is looking sick and not thriving and nothing that is done to it seems to help, then the roots may be damaged. They may have rotted, due to heavy poorly draining soil, or insects may be attacking them. Remember that this is a last resort desperate measure where you are attempting to keep the tree alive and you should then be extra careful with the after potting care of the plant.

Sometimes all a plant needs to maintain its strength is a change to a larger pot. If it is possible to do so without disturbing the roots, it is then not a problem and it can be done at any time of the year. This is usually done to allow for greater growth or if a plant is pot bound and in urgent need of re-potting to invigorate it while waiting for the right time of the year.

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Random Bonsai Tip

Use vinegar and water to remove moss but it is not as effective as using Limestone Ammonium Nitrate (LAN) and water. Be very careful not to spill any of the LAN on the roots of the bonsai tree as it may burn them and may in the worst case cause the tree to die. Carefully paint the LAN and water mix on the trunk of the bonsai tree and within days you should see the moss turn brown and die.