Beginners Corner - Repotting

by Dorothy Franz

Spring is generally accepted as the time for repotting, but there are exceptions. Figs, for example need warm weather, so in the Cape we repot them in December. Flowering trees are done after flowering. Pines late Spring and Junipers are usually repotted in November. Olives, what can I say, they seem to have a will of their own. I wait till they show movement, then I repot.

Experienced growers will start their repotting season towards the end of July through August and into September. This is usually because they have so many trees. To a novice grower, I recommend that they wait until they see little buds starting to swell.

The purpose of repotting is to renew depletted soil and thus give the plant new vigour and encourage growth. Before starting, get your material together i.e mixed soil, gauze to put over the holes, chopstick or a tool to unravel roots, tools for cutting roots, a spray bottle, and a basin filled with water and your pot. Make sure your cutting tool is sharp so that you do not get ragged edges which can lead to root rot or cuts that do not heal quickly.

Soil is only one element that contributes to the health of a plant but an important one.

  • It needs to have the ability to hold enough water without going sour.
  • The ability to allow sufficient air to filter through it.
  • Enough vegetable matter to hold nutrients.
  • Be rich in minerals
  • Be firm enough to hold the plant.

The test for a good soil mix is to compress a handful into a ball in your hand when moist. It should hold its shape but only just and very very slowly crumble.

Rainfall and wind exposure needs to be considered when mixing soil as well as the different growing needs of trees. For instance, a young tree, which is still developing, will require a mixture, which encourages the maximum amount of growth whereas an established tree only needs to keep its shape. Then there are the special needs of trees. Azaleas require an acid soil. Olives do not like being waterlogged but Swamp Cypress love it and Pines need mycorrhiza.

Prepare a basic mix and adjust for special needs. The most popular mix is three parts coarse sand or stone mixed with three parts potting mix made up of one part leaf mould and two parts loam. The stone should be multi-facetted and free from dust not smaller than 3mm, preferably 5 to 6 mm.

The first time you repot out of a nursery bag be prepared to encounter a solid block of soil. Loosen it with a spike and slowly work your way around the sides and bottom. It is usually better to remove all the soil. Pines and needle trees require mycorrhiza which is a symbiotic parasite, that is, it lives on the host plant but at the same time is beneficial to it. What it does is take vitamins and carbohydrates from the tree, but it gives the roots a better absorption quality. This fungus is species specific and grows on roots, enlarging the root surface. It also produces acids, which help to break down the soil, and organic material around the roots. So with pines some of the original soil must be put back into the pot when repotting.

Before one starts disturbing the root system, all wiring and pruning should have been done. Wiring a newly potted tree, which is unstable, will greatly damage the root hairs and root system. It is preferable to do wiring and pruning a couple of weeks before repotting so as to minimise stress to the plant. Do not water the plant the day before repotting. It is easier to work with slightly dry soil and it causes less damage.

One does not need to repot all the trees every year. Mames and very small trees should be done yearly. Other trees every two or three years and old established trees, probably every five years. Provided, of course, that they are fertilised regularly and that the health of the tree is maintained. Obviously if the tree is lifting out of its pot it needs to be repotted. Trees, which need to grow in size or girth, require repotting every year and should be placed in a large pot.

If one needs to repot at the incorrect time of the year because the health of the tree is in jeopardy then do an emergency repot. Lift it out, loosen the soil on the outer edges gently and put it into a larger pot where it fits in comfortably filling in new soil around it. This is really a transfer and not a repot. It will give the tree the space it needs for the present and a thorough repot can be done later at the correct time of the year.

In bonsai, as I have said many times in previous articles, timing is everything. Many trees are lost because repotting is undertaken at the wrong time or root pruning is too drastic without consideration being given to root and foliage balance. There is a supply and demand system operating - foliage demands, roots supply. When either is lacking, the result is trouble.

This is the time to sort out roots. Cut off larger roots with the cut facing down. Your aim is to get a three or five root system radiiating from the main trunk. A large root can be wired into a better position. Trim the finer roots working towards an eventual network of fine roots with minimum height, i.e. roots spread flat.

Once one has worked the soil in around the roots and the repotting is complete, dunk it into a basin of water to allow the gases to escape and clean air to fill the spaces. Place under shelter for three weeks and water as required. Trees with little or no foliage require less watering. No fertilizing should be done during this time.

When the tree shows signs that it has fully recovered the stress of repotting, it can go back on the bench and normal watering and fertilizing programmes can commence. Repotting is an essential part of maintaining the good health of a tree and if it is neglected, one finds that when it is undertaken it is difficult because the tree is root bound. Happy potting!

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