Developing a fine fibrous root system

Ujjawal Roy

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Hey all the Bonsai Nuts out there! Not particularly new to bonsai, but I'm still struggling with starting new bonsai from nursery stock or yamadori. Cutting off the tap root in order to encourage more fibrous roots to grow seems to kill the whole tree. I would appreciate if you all could help me out. I have a few questions regarding this :-
1) how should I cut off the tap root and not kill the tree?
2) I've seen people suggest cutting off the top of the tree in proportion to the root pruning to conserve water in the tree, however, I have also read that it's best to have as much foliage as possible as it helps generate new roots. Both are contradictory and i want a final verdict on this one.
3) does the soil particle size or shape influence the type of roots that the tree puts out?
4). How is the idea of putting nursery bought trees and yamadori in large Colanders after collecting them and regularly root pruning the protruding roots in order to encourage a more ramified root system before shifting it into a training pot?
Thank you!
 

Vance Wood

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A lot of what you can do is dependent on the species of tree. In general it is possible to cut the tap root, as you have imagined even though the ubiquitous tap root is all most non-existent in most nursery trees for a variety of reasons. The entire root mass can be cut in half (50%) horizontally as long as you have removed enough soil from the top of the root mass from the nursery container by scraping with your fingers until you find roots. I do this all of the time with Pines, Junipers, Maples, and Hinoki Cypress with no ill effects.
 

Cadillactaste

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🤔 I've not had a tree die, removing the tap root. There has to be something else that applies.

Each species has an ideal window of opportunity to work . As well as to the degree you can reduce their roots. Like conifer, one would do a half bare roots when you repot. I am not really a conifer person. But their energy comes from their foliage. Which has been stressed from day one learning this hobby of ours.

.
 

Cadillactaste

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I would like to say, I believe it was mentioned before (I don't expect you to have seen it.) substrate medium used along with ramification can help towards our goal of a better root system. Not always something seen right away.
 

Adair M

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The purpose of the tap root in trees is to affix the tree to the ground. For bonsai, we use wire to tie the tree into the pot. So the tree does not need any tap roots. We like to have lots of small “feeder roots” instead. These are the roots that absorb water and nutrients.

So, it’s difficult to determine why you have been killing trees based upon what you posted. Maybe you repotted in the wrong season. Maybe you don’t water when the tree needs it. Maybe you didn’t tie your tree into the pot so that it doesn’t move. if it moves in the pot, the slightest wind can break the fine roots if the trunk moves. There’s lots of possibilities.
 

River's Edge

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1) how should I cut off the tap root and not kill the tree?
2) I've seen people suggest cutting off the top of the tree in proportion to the root pruning to conserve water in the tree, however, I have also read that it's best to have as much foliage as possible as it helps generate new roots. Both are contradictory and i want a final verdict on this one.
3) does the soil particle size or shape influence the type of roots that the tree puts out?
4). How is the idea of putting nursery bought trees and yamadori in large Colanders after collecting them and regularly root pruning the protruding roots in order to encourage a more ramified root system before shifting it into a training pot?
1. You are rarely dealing with just a tap root. Roots are cut with respect to species and condition of the tree. No one method fits all!
2. Foliage produces the energy for root repair, keep the foliage after root work.
3. Yes, larger spaces between the particles promote larger roots, smaller spaces promote smaller finer roots.
4. If the colander is open to the air, roots will not protrude. Not a good choice for nursery bought tree or yamadori when first being worked on as the colanders tend to dry out more quickly, not a good thing after extensive root work or collection. The exception is if the colander is set in the ground and then the protruding roots can be trimmed and the tree re-positioned as it develops. Also with the colander in the ground it does not dry out so quickly.Sept16.jpeg
 

Ujjawal Roy

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Okay, seeing all the replies I'd like to point out that I am not from a western country or European. My trees are tropical varieties and nurseries here are not the usual shop like nurseries that you'd usually find. Trees in these nurseries are in poly bags in clay soil, the trees have a tap root which have feeder roots almost at the bottom, no feeder roots near the base. I usually "pot" in spring or during monsoon season. Trees that I buy from nurseries are not prebonsai, they are just trees that people usually pot in large pots outside their homes.
 

parhamr

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Okay, seeing all the replies I'd like to point out that I am not from a western country or European. My trees are tropical varieties and nurseries here are not the usual shop like nurseries that you'd usually find. Trees in these nurseries are in poly bags in clay soil, the trees have a tap root which have feeder roots almost at the bottom, no feeder roots near the base. I usually "pot" in spring or during monsoon season. Trees that I buy from nurseries are not prebonsai, they are just trees that people usually pot in large pots outside their homes.
There are an awful lot of Taiwan, Thailand, and Philippines bonsai accounts on Instagram. They might very well be using some of the same species as you, and have access to similar supplies.
 

River's Edge

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Okay, seeing all the replies I'd like to point out that I am not from a western country or European. My trees are tropical varieties and nurseries here are not the usual shop like nurseries that you'd usually find. Trees in these nurseries are in poly bags in clay soil, the trees have a tap root which have feeder roots almost at the bottom, no feeder roots near the base. I usually "pot" in spring or during monsoon season. Trees that I buy from nurseries are not prebonsai, they are just trees that people usually pot in large pots outside their homes.
Then it would be best to research techniques for the species you are interested in, taken care of by people in similar climates, purchasing similar material. To do that iI suspect t would be best to describe your situation from the outset.
 

Vali

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All these roots developed in one growing season, after this the tree was collected. I used different sized particle substrate, with some baked clay particles over 5 mm and some very fine perlite. I think root growth is more dependant on species than substrate particle size. Note that this is just my opinion, I don't have enough experience to generalise and say that this is a rule
 

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leatherback

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the trees have a tap root which have feeder roots almost at the bottom, no feeder roots near the base. I
This is a large component of your problem. If you cut the taproot you are left with a stump and virtually no roots.

The best course of action is the cautious routem untill you establish what works for you. This means you might have to repot the plant in open substrate in year one. POssible apply a wire tight around the taproot when replanting. Let it grow for the year. The next repotting period, you reduce the taproot to a place where you have a number of stronger side-roots. And on and on.

Unfortunately, a lot of videos online showcase people working plants harder than recommended for the regular Joe out there. If you do not have a polytunnel, misters (Or the option to mist when the tree needs it yourself) and you do not really know what you are doing in any case, a lot of the big steps taken can really easily cost you a tree. Add a step in between, and the trees will have a much better change of making it through and oddly enough, in many cases develop faster.
 

Mikecheck123

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I've seen people suggest cutting off the top of the tree in proportion to the root pruning to conserve water in the tree, however, I have also read that it's best to have as much foliage as possible as it helps generate new roots.
This isn't contradictory at all. A tree is a big feedback loop. Water up, food down.

If you muck around with one part of the system, the system can enter a downward spiral. Not enough water, not enough food, repeat until death.

So yes, more leaves gets you faster roots, but only if the leaves are functioning! I.e. you need sufficient roots to support those leaves in the first place.

That's why we do aggressive root work before the leaves extend. It prevents one part of the loop from ramping up into the downward spiral.

But I do maintenance root pruning in late August when leaves are at full strength. It works when you're not removing more than say 20% of the root mass. And the tree doesn't even notice.

Trust me I've been in your shoes with the contradictory information. But I've learned that any time I sense a contradiction, there's some nuance I was missing. Good luck!
 

hemmy

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I have a few seedlings but some species are only available in grown form like ficuses...
So yes, more leaves gets you faster roots, but only if the leaves are functioning! I.e. you need sufficient roots to support those leaves in the first place.
The above is an important point. But it should also be noted that with some tropical species (some ficus included) the leaves can be sustained with with sufficient humidity and resources from the vascular system of the trunk during large root reductions. The leaves have a thick cuticle that reduces water loss. Usually a bag, greenhouse or tent is required to reach those humidity levels and stop the drying winds. But ficus can also be treated like large cuttings if in the right climate (heat and humidity). In the case of removing all the roots, the leaves usually cannot be sustained. But the tree will re-sprout. This is a drastic development technique and not a refinement technique. On higher quality trees or climates without high heat and humidity this process can be taken slower by developing finer roots and gradual reduction of the larger roots. Grafting, ground layering, or in the case of most ficus just burying deeper can usually speed the development of the shallower roots.

I would do this type of work in the hottest and most humid time of year. But also knowing that you may need to provide some sun protection if the temperatures are too high and also limit overwatering from rainfall.
 

hemmy

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Here’s what Google has for Mumbai’s average temps and rainfall which is pretty far from our experience in most of the US. I would definitely ask your local bonsai society when to do drastic ficus repots. I might think April when night time lows are warm and right before the monsoon so that the roots can get established before the rains. But I might me wrong.
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I think you may be overthinking this. When cutting the taproot on seedlings or bareroot trees, always leave some small side roots. With large taproots I always cut them in stages during successive repottings, and I've never lost trees this way. I've done this with hundreds of trees, just always be sure to leave some roots even on fast-rooting trees like ficus.
 

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