Roots Demystified

[Andrew Legg]

Potting time, so time for rootwork and time to try to understand what makes the buggers tick.

There is plenty of info about roots out there, creating nebari, air layering, ground layering, toothpick method etc etc, so these we will leave out. What I'm angling for in this thread is info that helps us achieve healthy vigorous roots.

Of course, one thing most of us know who have been doing bonsai for a bit is that we aim for a good solid mass of fibrous root, evenly distributed about our mix in the growing medium. It is the fibrous roots that do the work of taking up moisture laden with all the goodies we stick in it. Yum. So how dome promote them?

I was reading on a site about creating good roots and was surprised to see written that a sharp mix promotes good root ramifications as when the root ends hit the sharp edges of the stone/sand, the sharp edge causes them to split, causing more branching in the root structure. Needless to say, this is a bonsai old wives tale! Any textbook on plant physiology will tell us that the growing tip of a root has a cap that is made from hard material that allows it to push through the soil undamaged. Moreso, this cap is actually lubricated by a "slime" generated bythe plant to ease it's passage on a microscopic level. So, if it is hard any slimy, it ain't splitting folks!

What the books will also tell us is that secondary roots are created by a chemical event in the sidewall of primary roots, and from what I can understand, the responsible chemicals are our buddies, the auxins! the presence of these auxins in the roots causes localised cellular division, which when continued results in new roots. There are all sorts of fancy terms for it all, but it seems it's upto the auxins. What causes the location of the cellular division I do to know (more research needed).

So, what have we learnt? More auxins = more fibrous roots. Makes perfect sense as auxins are produced in the growing tips of foliage, and the more of these there are the more moisture the tree is likely to need to hydrate them, and thus the link between growing tips and fine roots which take up moisture through the root hairs. Excellonto.

There is an old saying that in bonsai the top mirrors the bottom. Interestingly this seems to be true then. But unlike the way in which I think it is meant, I believe it to be reversed. The bottom actually mirrors the top. You create a good auxin factory with ramified branching, and the result is a good mass of fine feeder roots.

So this brings us back to the sharp sand/gravel mix myth. People don't believe these things for nothing right? Here I am of the opinion that folks who take the time to focus on what really goes into their mix will most likely focus on their ramification. This means they end up getting a better roots structure, but they incorrectly attribute it to the mix, instead of their good top-work.

I have found a lot of info that suggests a good open free draining mix promotes healthy roots. Why is this? Well, it seems all roots need two things to function. Water and air exchange. With a very fine mix you will get tons of water, but little open space for air. With a very course mix, loads of space for air, but little surface area to retain moisture, so perhaps this is where a good balance comes into it. Again, those of us who take the trouble to get a mix right will probably be getting this balance correct, so again, this could incorrectly be listed as the cause of good root ramification, where perhaps it would be more accurate to say that it supports good root health, not ramification itself. An old hand at bonsai once told me that he got fantastic growth on his junipers in a very free draining mix. His theory was that every time he watered, all the gas was displaced by water, but that as this new water drains out of his mix he gets new air drawn in from above. This combination of fresh water and fresh air at each watering created the growth. Again, makes perfect sense.

Finally from me a comment on olives. These are one of the local trees here that suffer from root rot. We have found here that the folks who use open free draining mixes are not struggling with rot as much as those who use very loamy mixes. We also find a spraying or drenching with a fungicide (in our case we use Alliette, an aluminium triss based fungicide) makes a great difference to olive health and we see very little of the branch dieback experienced by growers using heavy mixes. Incidentally one of our local non-bonsai nurserymen mentioned to me that many plants love a shot of trace metals, so this probably helps the olive vitality as well.

So, from what I can tell, a good free draining mix which retains moisture well, regular watering and feeding, and the occasional anti-fungal shot in the vein is what seems to create healthy roots. Of course I am talking generally here, so there will be species like swampies and pines that like wet or dry, and some plants liking acid or alkali mixes, but at the end of the day these can all be achieved.

Please feel,free to correct any of the above, and offer opinions and facts to supplement it. Look forward to hearing other ideas.

Cheerio,

Andrew

[Redsonic]

Fantastic article, Andrew. Really helped my understanding.

[treeman]

An old hand at bonsai once told me that he got fantastic growth on his junipers in a very free draining mix. His theory was that every time he watered, all the gas was displaced by water, but that as this new water drains out of his mix he gets new air drawn in from above. This combination of fresh water and fresh air at each watering created the growth. Again, makes perfect sense.

Generally good information Andrew however this part is not accurate. I've also agrued this common misconception with the orchid people. Plant roots do not and cannot rely on displacement of air in the media by water to get oxygen. It helps but the benefits are extremely small. Roots get their oxygen by diffusion. As roots and microbes take in oxygen, so more is replaced by the environment outside the pot. As you know, gases move from high concentration to low.
If plant roots had to rely on watering to breathe, they would be all dead in about 2 days.
The more open the mix the faster the gas exchange but of course this must be balanced with water holding capacity.

[Steve B]

So is the logical extension of this science that a "perfect" watering regime would be:
Step 1: completely wet the growing media (even submerging a pot in water for "X" mins to completely saturate the mix - X dependent on the media used).
Step 2: let the pot sit with unimpeded drainage until the "goldilocks" level of dryness in the media is achieved for that particular species/media.
Step 3: rinse and repeat.

Unrealistic generalisations, but I guess it's the philosophy behind good care and what I should be trying to achieve that has got me thinking. It seems to be supported by a lot of the "bonsai lore" around letting plants dry out somewhat between watering and getting an understanding of how quickly plants/media will dry out in different conditions.

Or can you avoid a lot of the art in understanding and maintaining balance by defaulting to an open inorganic mix and just watering and feeding frequently (Walter Pall style)?

[Josh]

Intersting article Andrew. I use 50/50 diatomite and pine nuggets and one of the reasons is I love the extremely fine root ball I get from it. I also grow in colanders and get incredibly fine masses of roots. I find with the colanders once the roots air prune around the edge they produce more roots internally. This makes sense from what I've read as the options are at the end of the roots to help them grow longer. If these are cut off the roots produce other routes from closer into the trunk giving you a finer root ball. Each time the roots reach the outside of the colander they are air pruned off and thus produce more finer roots. This also works with branches as the option is there to make the branch grow longer remove the end of the branch and it begins to back bud. Here is a site with some interesting info on ithttp://www.ext.colostate.edu/mg/gardennotes/145.html
I don't know the exact science but it works for me. Also I believe auxins in branches and ro I ts is different as branches grow toward light, roots grow away from light. So often you see a nice tree with 3 big roots coming out of it when a nice well rounded nebari wo u ld look much better, that can only be gotten from growing lots of roots around the tree.

Josh.

[Piscineidiot]

An old hand at bonsai once told me that he got fantastic growth on his junipers in a very free draining mix. His theory was that every time he watered, all the gas was displaced by water, but that as this new water drains out of his mix he gets new air drawn in from above. This combination of fresh water and fresh air at each watering created the growth. Again, makes perfect sense.

Generally good information Andrew however this part is not accurate. I've also agrued this common misconception with the orchid people. Plant roots do not and cannot rely on displacement of air in the media by water to get oxygen. It helps but the benefits are extremely small. Roots get their oxygen by diffusion. As roots and microbes take in oxygen, so more is replaced by the environment outside the pot. As you know, gases move from high concentration to low.
If plant roots had to rely on watering to breathe, they would be all dead in about 2 days.
The more open the mix the faster the gas exchange but of course this must be balanced with water holding capacity.

This post puts me in mind of a concept we tossed around when I did my undergrad in Marine Biology. That was the 'boundary layer'. Basically, the 'layer of water' immediately surrounding a coral needs to be regularly exchanged to prevent suffocation, and to facilitate waste excretion. The whole idea centers around the fact that corals both breathe and excrete via diffusion, which doesn't work once concentrations on both sides are equalized. So, for optimum health, it's necessary to refresh the water immediately surrounding them (which of course happens with tides and micro-currents etc.). I imagine plants would be similar? i.e. the water immediately surrounding the roots needs to be regularly refreshed for optimum diffusion (e.g. nutrient exchange and respiration) to occur. So easily water-logged/overly absorptive growing media might impede adequate drainage/water exchange, while too freely draining a growing medium might mean that the water flushes things away before the plant can absorb them (not to mention the danger of drying out). Of course both of these things appear to be able to be mitigated by the grower to some degree, which might explain the variety of approaches people seem to take when cultivating trees.

Does that sound about right?

[Elmar]

Sorry Josh,
Your link keeps bringing me to an old post where Steve discussed the Bonsai roll graphical illustration of the number of post you have made... I'm hoping this now works: http://www.ext.colostate.edu/mg/gardennotes/145.html




Cheers
Elmar

[Elmar]

Awesome idea for a post, Andrew! Wiki material for sure!


Cheers
Elmar

[MoGanic]

Hmm.. I always thought that root ramification was achieved in the same manner of branch ramification - pruning...

Auxins control top growth too but without correct pruning you get long leggy growth regardless of the auxin's presence.



Good eye opener and new perspectives help us rethink our otherwise stagnant thought processes.

Cheers,
Mo

[Andrew Legg]

An old hand at bonsai once told me that he got fantastic growth on his junipers in a very free draining mix. His theory was that every time he watered, all the gas was displaced by water, but that as this new water drains out of his mix he gets new air drawn in from above. This combination of fresh water and fresh air at each watering created the growth. Again, makes perfect sense.

Generally good information Andrew however this part is not accurate. I've also agrued this common misconception with the orchid people. Plant roots do not and cannot rely on displacement of air in the media by water to get oxygen. It helps but the benefits are extremely small. Roots get their oxygen by diffusion. As roots and microbes take in oxygen, so more is replaced by the environment outside the pot. As you know, gases move from high concentration to low.
If plant roots had to rely on watering to breathe, they would be all dead in about 2 days.
The more open the mix the faster the gas exchange but of course this must be balanced with water holding capacity.

Makes perfect sense Mike. Nice correction.

Cheers

[Andrew Legg]

Hmm.. I always thought that root ramification was achieved in the same manner of branch ramification - pruning...

Auxins control top growth too but without correct pruning you get long leggy growth regardless of the auxin's presence.



Good eye opener and new perspectives help us rethink our otherwise stagnant thought processes.

Cheers,
Mo

If that was the case Mo, you would get one long root. Problem is, moisture is only absorbed by the root hairs which as I understand it are dominantly on the root tips, so a single or a few growing tips would not sustain a decent foliage load (which is where the water evaporates).

Ho hum.

[MoGanic]

Hmm.. I always thought that root ramification was achieved in the same manner of branch ramification - pruning...

Auxins control top growth too but without correct pruning you get long leggy growth regardless of the auxin's presence.



Good eye opener and new perspectives help us rethink our otherwise stagnant thought processes.

Cheers,
Mo

If that was the case Mo, you would get one long root. Problem is, moisture is only absorbed by the root hairs which as I understand it are dominantly on the root tips, so a single or a few growing tips would not sustain a decent foliage load (which is where the water evaporates).

Ho hum.

Hmm... a thought, if I may... if the foliage relies on the roots to keep the water flowing up as it evaporates, then wouldn't it follow that the roots need to be in place prior to the foliage being able to grow and ramify?

This is requiring more research than what I can muster at work! Makes you wonder though don't it?

A plant in nature could be in soil that doesn't drain very well, is never root pruned, and is not pruned for ramification on the top either. Yet, it eventually becomes ramified on top and below. Also, how do these trees, with roots 5m in the ground (or sometimes deeper), get any air down there?

Also - we wouldn't get a long single root - as that's not what happens on top - inevitably, branching occurs, just slower when you don't prune.

But I do see what you're saying. Also, I read a paper at one point which outlined that roots generally split to avoid a blockage in their path. So a root is happily growing along and hits something dead on, it can't just turn around, so it starts growing in another direction or starts growing in two other directions. These are the "seeker" roots though that go out long in search of nutrients and water - not the feeder roots which, as you outlined, are developed differently all together.

Again, more research! WOOP!

Mo

[Naimul]

Hmm.. I always thought that root ramification was achieved in the same manner of branch ramification - pruning...

Auxins control top growth too but without correct pruning you get long leggy growth regardless of the auxin's presence.



Good eye opener and new perspectives help us rethink our otherwise stagnant thought processes.

Cheers,
Mo

If that was the case Mo, you would get one long root. Problem is, moisture is only absorbed by the root hairs which as I understand it are dominantly on the root tips, so a single or a few growing tips would not sustain a decent foliage load (which is where the water evaporates).

Ho hum.

Hmm... a thought, if I may... if the foliage relies on the roots to keep the water flowing up as it evaporates, then wouldn't it follow that the roots need to be in place prior to the foliage being able to grow and ramify?

This is requiring more research than what I can muster at work! Makes you wonder though don't it?

A plant in nature could be in soil that doesn't drain very well, is never root pruned, and is not pruned for ramification on the top either. Yet, it eventually becomes ramified on top and below. Also, how do these trees, with roots 5m in the ground (or sometimes deeper), get any air down there?

Also - we wouldn't get a long single root - as that's not what happens on top - inevitably, branching occurs, just slower when you don't prune.

But I do see what you're saying. Also, I read a paper at one point which outlined that roots generally split to avoid a blockage in their path. So a root is happily growing along and hits something dead on, it can't just turn around, so it starts growing in another direction or starts growing in two other directions. These are the "seeker" roots though that go out long in search of nutrients and water - not the feeder roots which, as you outlined, are developed differently all together.

Again, more research! WOOP!

Mo

From my knowledge, feeder roots dont develop any deeper than about 30cm underground (could be more or less depending on the species), and the only time roots would go any deeper, or extend any further is in search of water, nutrients, etc, and these roots would be th0e large, thick ones and eventually have feeder roots come out. And also the roots do grow a lot earlier than the foliage ( at least that is what i have observed when i used to grow bean sprouts for high school experiments and what not)

[Elmar]

Hmm... a thought, if I may... if the foliage relies on the roots to keep the water flowing up as it evaporates, then wouldn't it follow that the roots need to be in place prior to the foliage being able to grow and ramify?
...
Mo

I thought that if we trim the branches, the leaves that grow back should be more in number BUT the overall surface area of the leaves then are the same as those that were originally cut of for the ramification to occur...

[Josh]

Hmm.. I always thought that root ramification was achieved in the same manner of branch ramification - pruning...

Auxins control top growth too but without correct pruning you get long leggy growth regardless of the auxin's presence.



Good eye opener and new perspectives help us rethink our otherwise stagnant thought processes.

Cheers,
Mo

Pruning will create taper in your roots. It also encourages roots to produce finer roots along the main root.