Repotting & Transplanting - How, When & Why

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Some basic suggestions for repotting, concerning the specifics of why repotting is done, when it is done and why.

PURPOSE
Plants are repotted for a variety of purposes. 1) To refresh the soil and improve drainage - This is done periodically as a maintenance operation. The soil breaks down over time with repeated watering as the organic components decompose and compact. As the soil texture grows finer, drainage is impeded and root rot can result. Repotting will enable you to restore the drainage conditions to maintain the plant's health.

2)To obtain a more compact root system - As the tree grows, its root system will also grow, filling the available container space. This space is important to maintain a porous texture to the soil so that the roots and the complex communities of microorganisms in the soil can obtain air to maintain a healthy environment. Left alone, the tree would eventually fill all the available space with roots, wrap around the container, and begin to push the tree itself out of the container. Repotting enables us to develop a more compact, efficient root system with a higher percentage of fine feeder roots.

3) To change to a larger container - for growth, or to a bonsai pot or intermediate growing container. Plants removed from nursery containers usually need to be repotted to an intermediate size container before being tranferred directly to a bonsai pot. this is because the nursery pot is taller and the root system has not usually developed the compactness and fine branching that is necessary to support the tree in a shallow bonsai pot. The tree is transferred to a "growing container" which is of an intermediate size, perhaps half the depth of the nursery container and twice its width. A year or two in this environment lets the tree recover and eases the transition to the bonsai container.

Collected materials are generally potted in any serviceable container that acommodates the existing root system. Unless the tree is an especially vigorously rooting species (wisteria, bougainvillea, willow, etc) one is usually careful to disturb as little of the original collected roots at the first potting in order to ensure that the tree survives its transition to container life. Two years is considered a basic, minimum recovery period. Look for active growth.

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For young trees in bonsai containers, repotting is generally done every one to two years. You can get a good idea as to the condition of the root system after a year's growth by cutting the tie wires and removing the tree from its container. Is the pot lined with feeder roots and actively growing (white) tips or is the soil putrid and smelly? Are the roots circling the pot? What is the general health of the tree? Can a chopstick not be pushed into the soil about halfway between the tree and the container edge? How fast is water draining through the soil? Is the surface of the soil hard and crusty? Is it repelling water? Each of these may be a sign that the tree is ready for repotting.

TIMING OF REPOTTING

Repotting is usually conducted after a tree has just entered dormancy or just before it begins active growth. Tropical varieties can be repotted throughout the year. Plants generally flower during dormancy, so you can look at this as an indicator. Plum and apricot flower early in the spring, wisteria later and azalea toward early summer. Deciduous varieties can be transplanted in the fall after they have lost their leaves, when there is no danger of "indian summer conditions" but before the frosty weather turns to freezing.

Conifers may be transplanted in the fall, but you may have a better response from them if you plant in the mid spring. It is said that the flowering of the wisteria is an indicator as to the ending of the period for transplanting pines. This is typically March in this area.

EMERGENCY REPOTTING

For various reasons an emergency repotting may be required. If conditions of root rot are noted, if the tree falls off the bench or the pot breaks an emergency repotting may be in order. If the repotting is "out of season" particular care must be taken. If the tree is generally healthy, the best course of action is to limit the repotting operation to replacing to lightly pruning the root tips without breaking the root ball, and restoring it to the same or a new container adding just the required amount of fresh soil.

If the repotting is being done because water is not penetrating the soil, the upper quarter of the soil, or approximately 1 to 1-1/2 inches of soil may be removed and replaced with fresh soil. If the situation is particularly bad, consider removing sections of root and soil from the four corners of the pot and replacing with fresh medium.

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A. GET THE MATERIALS READY

Nothing is worse than leaving your tree unearthed while you search for the right pot, soil and materials. Before you begin ensure that you have the following items:

1. Chopsticks
2. Root Pruning Shears
3. Root cutters, small or large
4. Root Saw
5. Pot (cleaned and ready)
6. Drainage screen installed
7. Wire for tying the tree into place and securing drainage screen
8. Wire cutters for trimming wire
9. Wire pliers for tightening the tie wires
10. Prepare soil for repotting. The preparation of soil is the subject of a separate article, but you will want to be sure you have plenty of soil on hand before you begin the repotting operation. The soil should be dry, but not "bone dry." The soil should be screened with a sifter to remove fines and dust that could clog container and obstruct drainage.
11. Watering nozzle and hose
12. Tub or container for soaking the tree
13. Spray bottle filled with water
14. Long fiber sphagnum moss, (use "Canadian long-fiber moss." NOT ground peat moss)
15. Soil Scoops for distributing soil
16. Moss spores or collected moss, if desired

B. PREPARE THE NEW CONTAINER
If the tree is going back into the same container you will need to remove it from the container first, then return to this step before proceeding.

1. Wash the old container. Scrub out any old soil with a vegetable brush. If the previous occupant of this pot met an untimely death, it might be sensible to wash out the container with a solution containing a 5% Clorox solution to disinfect it. Be sure to rinse the container thoroughly to remove the bleach residue.

2. Identify the "front" of the container. Some pots have defects, cracks or warping that makes the front easy to find. If you can't see any difference, don't worry about it.

3. Replace the drainage screen. The screen should completely cover the drainage holes and it may be secured with a staple-shaped piece of wire that pokes through the drainage holes and is bent outward on the opposite side.

4. Add tie-in wires. These will be used to secure the tree. Tie-in arrangements for group plantings and cascade trees can be the most complex. In general you will want to have a minimum of four wire ends for tying, which means two wires. Make the wires about 3/4 of the circumference of the pot. A little longer for a cascade pot. A little deeper for a tray - 1/2 the circumference.

5. From the bottom of the pot, pass the wires through the drainage holes and distribute the wire ends by tucking them over the four corners of the pot, or approximate that position on hex or round pots.


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The general procedure for repotting is to cut any tie wires with a wire cutter and remove the tree from its container. If the tree is well established, it may have compacted itself against the walls of the container and it may be necessary to run a knife or root hook around the circumference of the pot in order to extract the tree.

If the container has a lip that turns in at the top, it may be even more difficult to extract the tree. You'll likely have to take a sharp knife and cut the root ball around the container about 1/2 inch in from the container's edge.

Roots sometimes work their way out through the drainage holes. You'll need to check here and cut away any roots.

If the tree is particularly stubborn and you're sure that you have taken the steps described above. Get some help. Have an assistant support the pot on its side. You can use a dowel and a mallet, if necessary, to push the tree out of the pot through the drainage holes. Be especially careful if this is an aged tree or delicate tree.


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C) INSPECT THE ROOTS
Work in the shade away from direct sunlight. Dry roots are dead roots. If you're interrupted, cover the tree's roots with a damp rag and get back to it as soon as possible. Once the tree is out of the pot, inspect the root system as described above. Does it wind around the pot? Is the tree growing well? Does the soil have a bad odor? Is the root ball well distributed? Are the root tips growing actively? Is the container packed full of fibrous thick roots that aren't doing you or the plant any real good? If repotting is warranted:

D) COMB OUT THE ROOTBALL
Using a root hook and chopsticks, comb out the rootball. You may be surprised to find that the length of roots may be several times the length of the container. Periodically mist the roots with the spray bottle.



E) TRIM BACK THE ROOT SYSTEM
Keep in mind that the most efficient roots are the smaller feeder roots. The larger roots do have some function in that they store starches for plants during dormancy, but they aren't particularly effective at absorbing moisture. You can generally prune away a lot of root mass provided you retain the fibrous roots.



Tools available for root pruning include

Root saws for cutting through larger roots. You may find that the tree has developed roots at two layers within the pot. A nice radial root system at the soil level and another one below at the bottom of the pot. You want to encourage the roots that will give the trunk the best apparent taper.

Root cutters for cutting thick roots off cleanly and easily.

Shears for cutting back fine roots and root tips. Simply cutting the root tips is enough to encourage the tree to develop more and finer roots. You can expect that shears used for root work will dull and be subjected to the occasional nick from stones embedded in the soil. For that reason, use older shears for root work or get a pair that is strong and suited to that practice.

Save your best shears for the top of your tree.



F) Through a combination of saw, root cutters and shears, you should have reduced and improved the distribution of the root system. If one side of the tree is particularly deficient in roots, go ahead and leave the few roots on that side alone with the exception of a light trimming with the scissor, even if this means leaving a few long roots on that side. Prune the roots on the opposite side more severely to encourage a redistribution of vigor.

In general, deciduous trees are more tolerant of aggressive root pruning than conifers. Some pines, particularly older trees and cork bark trees are very intolerant of having their roots disturbed. If a pine is healthy it should not have the entire soil removed at one time. Instead, if you suspect that field soil still remains work on one-half or one-third or the root ball at one time and leave the other portion alone. If the tree is clearly suffering from poor drainage conditions you may want to work more aggressively to ensure that you have all of the field soil (clay) removed. It is generally safe to remove much if not all of the existing soil from a decidous tree without problems.

6) If no roots have developed on one side of the trunk, consider wounding the trunk in that area and applying rooting hormone. Use a knife to make a small nick or series of nicks along the bare area of the trunk at the level at which you hope to have roots emerge. Chopped sphagnum moss may be applied to the surface of the soil in that area to encourage humidity that helps to encourage root growth. Dust the area with rooting hormone powder (Dip-N-Gro) or paint on a diluted concentration of liquid rooting hormone (Rootone). Not a bad time to take a quick photo or make a sketch so you'll know if you were successful!



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Transplanting a bonsai is required occasionally to keep the plant healthy and to meet your own artistic goals. At the end of this article are some links to additional topics, which explain in more detail why repotting is necessary, and discuss timing, tools and methods.

If you've never repotted a tree it would be a good idea to familiarize yourself with each of these topics before getting started. [*]Why do we repot bonsai?[*]When to repot?[*]Getting the tree out of its pot[*]Trimming back the roots[*]Prepare the container for transplant.

[b:d69f1f12b5]REPLANTING THE TREE[/b:d69f1f12b5]

1. Fill the container about 1/3 full with soil arranged in a small volcano-shaped mound.


Position the tree over the mound and with your hands distributed across the roots, work it down into the soil with a twisting motion.


2) Ensure that you have the trunk positioned where it belongs and that the fronts of the pot and tree are facing in the correct direction. This is mainly an aesthetic issue to be discussed elsewhere; however, the trunk is usually arranged not dead-center in the pot but a bit toward the rear and favoring the left side or the right, depending on the line of the trunk and the placement of the first branch. This position is intended to increase the apparent depth of the container and also balance the visual mass, and is a matter of personal taste. The position of major roots or deadwood may make the position of the tree less flexible.

2) Add soil to the pot using the soil scoops. Take care to distribute the roots evenly around the pot. Using chopsticks, work the soil into and around the roots. You can strike the container with your balled fist or lightly with a rubber mallet to help to settle the soil.

3) Tie the tree in place using the tie wires and pliers.

4) Continue this operation of adding soil and working it in until you're sure that all of the air spaces have been filled. Shaking the container from side to side may help to settle it more.

5) A slightly finer mix may be used in the top 1/2 inch or so of the pot. Work this in with chopsticks as well.

[b:d69f1f12b5]Next Steps:[/b:d69f1f12b5][*]Watering-in

[b:d69f1f12b5]More Information:[/b:d69f1f12b5][*]What's the big fuss about soil ingredients?[*](Even more information at bonsaiTALK Links under Techniques>>Transplanting)

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H) WATERING-IN

Watering-in helps to insure that any fines that remain in the bonsai soil after planting are flushed through the soil and out the drainage holes. If improper or incomplete watering is done after repotting, these fines will remain suspended in the pot, where they can obstruct drainage and cause problems down the road. Even the best bonsai soils will break down a bit under the force of repotting, either through abrasion or pressure in settling the soil. Flushing this material out takes just a few minutes of extra effort.

Using a hose or watering can with a fine rose mounted, thoroughly irrigate the tree and allow the water to flow through the drainage holes until it runs clear. This may take 5 to 10 minutes or so, depending on the container volume and the amount of suspended matter.

You may cover the surface of the pot with a light layer of chopped long-fiber sphagnum moss to help retain humidity. The moss should not cover more than about 1/3 of the soil surface. The tree should be returned to its growing area. It's particularly important that the pot be allowed to have sun to let it warm to encourage the roots to grow and recover. Mist the tree, but do not water again until the soil has begun to dry somewhat.

I) When the tree has recovered and is actively growing you may decide to add top dressing or moss. Moss spores may be added in a light dusting over the top layer. Follow the instructions on the package. Within a month or so moss will have begun to develop. Alternatively, moss may be harvested from another tree, but moss that grows in place usually is more pleasing. Do not allow the moss to cover more than 1/4 of the surface of the pot, and be sure that it is not allowed to grow up the tree and onto the bark. Avoid long-fibered moss and all kinds of hornwort. These tend to clog the soil surface and impede drainage.

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