| Editor's note: The advanced techniques depicted in this article are not appropriate for all growers and all species. Drastic pruning should never be undertaken lightly. It is often prudent to perform extensive work to different parts of the root system in alternating years to limit stress on the tree. Experience is your guide. |
In bonsai there is no more drastic measure taken than root pruning.
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Fig 1. A Healthy Root System |
For some plants a drastic pruning may be the kiss of death, for others, it will restore vitality and bring forth many bounties. Root pruning is but one measure for restoring vitality in a weak plant. In this essay, drastic root pruning will be studied and photos will be provided for backup, they help reinforce those thousand words.
(Oh, and one caveat, this is mostly about deciduous trees. Junipers have their own time schedule and can’t be hurried up for anyone. Trees can be lost with these procedures and I take no responsibility if you lose your best specimen!)The keys to a healthy root system can be summed up in four points:
1. Adequate soil drainage and moisture retention.
1. Adequate soil drainage and moisture retention.
2. Proper watering technique & water quality.
3. Soil fertility for stimulation and growth
4. Rejuvenation of feeder roots through root pruning.
4. Rejuvenation of feeder roots through root pruning.
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Fig 2. Roots |
When the first three points have been mastered, the next logical step is to master root pruning. Root pruning helps the plants in many ways.
- First, It develops a compact root system full of feeder roots that actually do the working part of the fuel exchange. This feeder root system can take up the necessary water and nutrients for proper growth above the soil line.
- Second, with a compact roots system bonsai aesthetics can come into play with additional pot choices for artistic compositions, and
- Third, fibrous root systems can achieve the kind of branch ramification necessary for proper bonsai aesthetics.
Ever wonder why farmers, for no apparent reason, will remove an entire orchard and replace with some new type of crop? This is done with grapes and fruit trees in 10 to 15 years cycles. Farmers do not have the luxury of digging up the entire orchard for a root prune. Drastic top pruning is done on a yearly basis and this pruning stimulates the plant into a more rigorous growing cycle. This can be done with nearly all plants, for a while! Without drastic root pruning, the plant will exhaust its root system and become weak. In fruit trees and grapes, this may happen in as little as 10 or 15 years. While the plants would surely live long useful lives and still produce fruit, it is not as productive as it was in its youth when it responded to top pruning only.
Are my plants healthy?
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Fig 3. Roots |
Look at the plants you take care of daily. Are the leaves the same color they once were? Are the branches responding to pinching and pruning like they did 5 years ago? If not it could be a sign that the root system has bogged down and is in need of revitalization. Do you inspect the roots when you repot? Let's move on then.
On inspection if you notice long stringy black roots that smell bad and are hollow, it is a clear case or rotted roots. This is a problem that needs to be corrected before any procedures on drastic root pruning can take place. This rot problem is usually caused by one of two issues. Alternatively, it may be a combination of the two, which has caused the problem. If this is the case, then a lot of experimentation will have to be done to come up with the correct solution. Water is the most prevalent problem with root rot. Soil that retains too much water is the second leading problem. So obviously, the solution would be to have a fast draining loose soil and the proper amount of water when needed. This is of course simplified, but this is the experimentation part. Soil mixes will have to played with to see what works best in a given location. Watering will need to be done regularly, but only as needed. With the proper soil, watering is done on a regular basis. One may find that a few hours difference in a day can make a large difference if there is a large variance in the temperatures.
On inspection if you notice long stringy black roots that smell bad and are hollow, it is a clear case or rotted roots. This is a problem that needs to be corrected before any procedures on drastic root pruning can take place. This rot problem is usually caused by one of two issues. Alternatively, it may be a combination of the two, which has caused the problem. If this is the case, then a lot of experimentation will have to be done to come up with the correct solution. Water is the most prevalent problem with root rot. Soil that retains too much water is the second leading problem. So obviously, the solution would be to have a fast draining loose soil and the proper amount of water when needed. This is of course simplified, but this is the experimentation part. Soil mixes will have to played with to see what works best in a given location. Watering will need to be done regularly, but only as needed. With the proper soil, watering is done on a regular basis. One may find that a few hours difference in a day can make a large difference if there is a large variance in the temperatures.
Ever wonder why farmers will remove an entire orchard and replace it with some new type of crop?
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Fig 4. Sawing out the stubs |
Now with the root rot issue solved we can move on to the roots. Roots behave no differently than a good branch system above the ground. Most people have no problem in doing semi-drastic pruning to the top of the tree. Hey, if I cut too much the tree will just put out new shoots and in a season or two we will have more branches again. Ahhh… but the roots will behave just the same way. Prune them back hard and the will just bud and grow more roots. What a novel concept. Just what we want to happen! Thinking about that farmer again, the farmer knows that to get good production the next season, top pruning has to be carried out in just the right time of year. That’s why Franklin made the Farmers Almanac; it had the precise dates to carry out pruning to insure maximum harvest for the next year. Of course, now we have computer models and blackberries to keep a running log of farming activities. This drastic top pruning spurs adventious buds to sprout and increase ramification. More branches, more fruit. Think of a tree as growing on a mirror at the soil line. The tree should be a reflection of itself above the ground as well as below. This reflection is maintained by the same aggressive pruning as done above the ground.
If we prune too much I will kill the thing…
If we prune too much I will kill the thing…
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Fig 5. Feeder Roots do the |
This could be true. There is a fine line with doing any drastic pruning, whether on top or down below. The key is the health of the tree. If the tree is healthy and the pruning is done correctly, then the tree will reward the grower with many new shoots and buds. Flowers will be better and fruit will be larger. Leaf size can reduce smaller and internodes will be shorter. This is all due to the smaller more compact root ball. Remember the mirror thing, reflection.
During the course of a thread, here a few days ago, this fellow needed help on a small juniper. Many replies gave a wealth of information on how best to proceed with this juniper. The juniper had been drastic pruned. It was said that the tree could probably undergo a first styling with a small amount of wire. This would be about it for the season with the remainder of the year reserved for a rest period. Then the fellow concluded that he thought it might be best to go ahead and repot the specimen to a growing container. His reasoning was thus, “Since I didn’t mess with the roots, I should have no problem with repotting in a growing vessel”.
During the course of a thread, here a few days ago, this fellow needed help on a small juniper. Many replies gave a wealth of information on how best to proceed with this juniper. The juniper had been drastic pruned. It was said that the tree could probably undergo a first styling with a small amount of wire. This would be about it for the season with the remainder of the year reserved for a rest period. Then the fellow concluded that he thought it might be best to go ahead and repot the specimen to a growing container. His reasoning was thus, “Since I didn’t mess with the roots, I should have no problem with repotting in a growing vessel”.
Why? If one is not going to mess with the roots and prepare the plant for the procedures of grow out, why do it? Why stress that plant any more with this useless procedure? The whole purpose of planting a plant out to increase size is to gain maximum benefit. Not drastically pruning the roots before this procedure is setting yourself up for failure.
I think I’m ready, what do I do?
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Fig 6. Compact Root System |
Prepare the plant the year before the repot. Root rot should have be under control, soil mix should be best for the climate, and watering habits are now routine. Planting vessel should be prepared with the soil, screen and tie wires. If a growing box is to be used, it should be adequately ventilated for fresh air and provision for blocking it up should be made. If the plant is going to the ground, then a suitable hole larger than the plants drip line should be prepared*. (note; If the hole lies over hardpan and it is less than two feet from the surface, consider using a grow box.) Adequate soil should be prepared to fill the hole.
The actual procedure is shown in the picture portion. The timeframe for a growing plant should be an every-other-year affair. On completion of the first year, there may not be much evidence of increased growth. The increased growth comes in year two.
The actual procedure is shown in the picture portion. The timeframe for a growing plant should be an every-other-year affair. On completion of the first year, there may not be much evidence of increased growth. The increased growth comes in year two.
- First year stabilizes the plant.
- Then in year two, those new root fibers really start to do their work. This is when the increased activity and new buds are evident.
- After year two, the procedure is started again. Root prune, then another year of growth. A tree could be left in for another year, but the revitalization of the root pruning really helps keep the tree tiptop shape.
In Japan, this growth and recovery regimen is done on a continual basis between exhibits. A tree will be exhibited and then prepared the next four years for the next exhibit.
A plant may be left in for three years for special needs. This may the growing of branches, or the closing of large chop wounds. Wounds are fast to close in year three of a drastic root chop and left alone. Scar tissue builds fast with correct dressing of the scar. In fact, it may be so fast that it may have to be slowed down to not build to thick of scar tissue. This would be done by planting back in a show pot.
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Fig 7. The Roots I removed |
The quince in this repotting sequence was purchased four years ago. Even though I have no pictures of the roots from four years ago I can tell you they were bad. I bought the tree at Muranaka’s Bonsai Nursery and that will be "enough said" for some of you out there. When I did the first repot, I had to take off the initial roots with a cleaver! I made a chop straight across the entire root mass and just hoped for the best.
The tree was allowed to grow in a bonsai pot. I had no need for actually increasing anything as far as size. I just wanted to improve the root system by drastic pruning. Each year the root system has been chased up the mass towards the root crown.
This year's work
This year marks the final pruning by drastic means. The future repots will just be clean up of the root system. I have finally reached the best possible root system for this tree in terms of depth and volume. Of course, nebari is another matter, and that is ongoing. The plant was taken out of the container and the roots combed out. In the one photo, the roots are white and very healthy. No black rotted roots are visible on this plant. I use straight akadama and swear by this expensive Japanese "elixir of life" for a bonsai.
This year marks the final pruning by drastic means. The future repots will just be clean up of the root system. I have finally reached the best possible root system for this tree in terms of depth and volume. Of course, nebari is another matter, and that is ongoing. The plant was taken out of the container and the roots combed out. In the one photo, the roots are white and very healthy. No black rotted roots are visible on this plant. I use straight akadama and swear by this expensive Japanese "elixir of life" for a bonsai.
The chopstick in (Figure 3) marks a point in the root ball that divides into a top portion and a lower portion. This is separated by a ring of area with out roots, a natural break for me to remove the last remnants of the remaining claw like root system this plant had. The plant was sawed free of these last root stubs and I was left with an almost perfectly flat compact root system. This root system is only 1.5 inches thick and will now allow many choices for pots in the future. This procedure took three years to complete. Not bad by bonsai years.
The remaining task left was to remove the portion of the roots not needed to sustain the plant. It is
through the re-growth of these roots that additional branching and ramification can take place. This root pad may seem very small to some, but I assure you this is just what is needed in the early spring when the engine come alive and starts to send the sap flowing through the veins of the tree. This small root system will start moving and growing with breakneck speed until it fully fills this pot with fresh new white feeder roots by fall. On the bench is a hocky puck size disc of the roots that I cut off. This was about 1" thick. In the photo you can see the remnants of how large the claw like roots were in ralation to the size of the trunk. I would have needed a pot 6" deep to plant this thing in.
Figure 7 show the size of the previous root size compared to how small I have drastically pruned it back. It is only 1" thick and 3" across in diameter.
The deep, oval pot was chosen because it is smaller in diameter than the pot before, and the increased depth will give me someplace for the new final roots to grow for next years showy pot. Probably a low oval glazed pot that compliments the flowers.
Hope this energizes some to try some drastic root pruning to invigorate your tired plants. Until the next installment,
The remaining task left was to remove the portion of the roots not needed to sustain the plant. It is
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Fig 8. Completed |
Figure 7 show the size of the previous root size compared to how small I have drastically pruned it back. It is only 1" thick and 3" across in diameter.
The deep, oval pot was chosen because it is smaller in diameter than the pot before, and the increased depth will give me someplace for the new final roots to grow for next years showy pot. Probably a low oval glazed pot that compliments the flowers.
Hope this energizes some to try some drastic root pruning to invigorate your tired plants. Until the next installment,
AJKeppler
Photos & Text by Al Keppler, used with Permission
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