AusBonsai

I was re-potting over the weekend and I thought of an interesting way to look at your soil mix and how it performs might be to look at the root growth that you get from it.
As soil mixes themselves are highly debated i thought that we might be able to come up with a problem-solution type of matrix to help improve your mix whatever that may be.

I will start by making a list of observed issues and perhaps people could suggest ways to solve these issues by changing qualities of the mix.

01- Top few cm's of pots soil devoid of roots - perhaps a smaller grain particle to the upper portion of my potting media in the hope this will hold more moisture in this region and encourage more roots??
02- Roots mainly at base of pot/ curling around pot base.
03- Roots only on the extremities of the pot / no and or dead interior roots.
04- Roots only on the upper part of mix.
05- Rotting roots
06- Long ropey roots

That’s a few i could think of of the top of my head. Any more issues people have observed or ideas why those listed might occur? Too wet, too dry, not enough air space? How might you combat this within your mix? Larger particles, smaller particles, more water holding material, less water holding material etc.

If we can work this up as a group i think it could become a very useful resource.

I have a bit of a problem in some of my trees with 01. So this year i have added a smaller grain particle to the upper portion of my potting media in the hope this will hold more moisture in this region and encourage more roots. Do people think this is an accurate path of actions? Can anyone else think of more problems and or solutions?

Joe

A great idea, a list of observations and how to improve on them!

01 - I have had the issue of the top few cm's of pots devoid of roots (or small crispy roots) too. I think smaller particles would help. Last year I used sphagnum moss on the soil surface to protect the small roots a little more. I think that there are more roots than I have previously observed.

02- Roots mainly at base of pot/ curling around pot base. I've had this too but not sure what to do about it?

Spagnum is a good idea.

The coiling roots may be after the cooler temps low down and or the water that pools on the bottom of the pot, perhaps a mix that is too dry?... not sure... anyone else have any ideas?

Excellent thread Jow

The issue could be positioning of the tree i.e - too much sun, wind, shade, and etc can impact on how the tree distributes its roots around the pot ??


Cheers.

I have dug out two trees this recent weekend and both were in very coarse mix. I found that they both had a lot of general rootage.

Usually I find a large amount of roots around the outside and little in the middle if a tree is in an organic mix. I have always figured they struggle to find their way through the small gaps so they just run to the edge and spin around.

My theory is not so much about needing small particles so the soil stays wet it is more that there needs to be sufficient oxygen for the roots to get between particles.

Wet roots I find tend to not grow. (dead dry ones dont either of course) By having a larger particle there is space between the elements to let the roots "fill the space" and if the particles are irregular in shape they have edges and angles for surface tension to hold water. The roots travel between the particles get the water and thus fill in the gaps.

I am sure there are scientific explanations or contradictions to my theory but this is what I have found. Large particle = good roots, organic and fines = roots running around the edge of the pot.

I like the idea of spagnum as a mulch I will try that on my shallow pots this year perhaps.
Does it come to life and then you can never get rid of it though? I dont want to end up with a moss problem.

Chris,

I have had the moss 'come to life' but only from roots growing into it, I haven't had it grow and become a problem.

Jow wrote: 01- Top few cm's of pots soil devoid of roots - perhaps a smaller grain particle to the upper portion of my potting media in the hope this will hold more moisture in this region and encourage more roots??
02- Roots mainly at base of pot/ curling around pot base.
03- Roots only on the extremities of the pot / no and or dead interior roots.
04- Roots only on the upper part of mix.
05- Rotting roots
06- Long ropey roots

Likely causes:
1 - As you stated, top too dry.
2 - Also too dry. The roots are relying on the pooling of water at the base of the pot.
3 - Not enough aeration. Roots are mostly at the extremities of the media where they have better access to air.
4 - Mix is too wet. Roots are populating the area that dries out first.
5 - Mix too wet OR not enough aeration OR pathogen is present.
6 - Not enough aeration. Could also be linked to low phosphorus and high nitrogen availability. Can also be just a symptom of another stress (i.e. heat stress or insect damage etc).

Hi Joe and the rest of you.

Issue 1: Mulch with Sphagnum or Pea straw

If you are talking about improving the rootball quality in pre-bonsai, then I reckon there is a blanket answer for issues 2-6 listed here.

Collanders or aquatic pots.

Aeration, drainage, root division due to air pruning, an overall evening out of the root mass and you can "pimp" less than spectacular growing mixes with them.

Cheers,
Mojo

Not sure whether I'm on track here but I feel that lots of roots around the edges/ base of the pot is a function of root growth rather than mix. Roots grow away from the tree until they hit the pot then follow the pot around (and around and around). So ALL roots will be growing around the edges of the pot making this the most crowded area while only a few roots will have grown through any interior part before getting to the edges.

Could 06 - long ropey roots be to do with the species? Some species have roots that ramify easily eg maple while others have long, unbranched roots eg elm.

One factor that i notice when repotting is a layer of very fine material, alsmost mud on the surface. I thought maybe its the fine material that the moss was growing on when I transplanted it but seems to be greater depth than that. Possible that moss 'catches' and holds fine particles (that is its function in nature - to increase soil depth and capture nutrients) to increase the depth of fine material. Also possible that the surface is the place where decomposition is most active (air, moisture, light, etc) so the organic particles in the mix break down faster there?

05 rotting roots would usually be attributed to over wet/ poor drainage. Sometimes I see it as a result of roots dying from other causes eg dry (common with surface roots cut short). The dead root will eventually rot, even in well drained mix.

Chris, spagnum is VERY difficult to grow. It has very specific environmental needs so it is unlikely to become a problem for you.

Shibui is spot on. Trees in the ground grow their roots away from the trunk as far as they can to maximise the collection of water and nutrients. They are going to do the same thing in a pot until they can grow no further away, so they curl around the bottom of the pot. This is one of the reasons that we root prune, to get better ramification of the root system and therefore more feeder roots as the main absorption of moisture and nutrients is at the growing tip and the fine, hairlike feeder roots just behind the growing tip.

I dont find all my trees wrap around the bottom of the pot.
Just the ones in mix which isnt open and/or dries out/ doesnt rewet easily.

On others I find that the roots often arent radial but running aroudn all over the inside of the pot through the middle of the mix, anywhere they can find really.

I just repotted my trident cuttings that were taken 2 yrs ago. They were in 2ltr ice cream containers in diatomite and pine bark mix.
They had completely colonised the containers with fine feeders throughout the mix top to bottom.
But there were roots circling the edges in the bottom third of the container and sitting in a layer 2cm thick at the bottom. These were not fine feeders but the thicker soft white roots and I think they were there because there was no more room in the container (completely colonised)... Now that the cuttings are established, it will be annual repots for now on.
I can also see the logic in the root issues stated above and believe that the mix can be altered to attain a better outcome for certain problems
Interesting read
Cheers, Dario.

Hi Joe, I have just spent the afternoon finishing my deciduous potting and your issues were very much in my mind.
I found no evidence of the problems you have encountered with the exception of the one tree and I know I was slack in sieving the potting mix with that tree when I potted it last year, the centre of the pot was devoid of roots they were all coiled around the outside of the pot. I believe this is because the potting mix was too wet and the fines which were not sieved out had clogged the mix up.
I would be very reluctant to add more fines to your mix in fact quite the reverse.
In most cases the pots were full of root right to the surface and in some cases they had pushed above the surface where the ferts had been sitting.
I wonder if there my be some advantage in you putting your deciduous trees in slightly deeper pots so as to keep them a bit cooler over the summer months, I also thought you may need some barrels of water around the trees to increase the humidity during the hot weather.
I know I live in a much cooler climate but I have been using the same mix long before I moved up here and my backyard in footscray was north facing and very hot. My trees have always lived with some sort of garden around them which could be a big help.
Craigw

I repotted seven trees today. They came out of a variety of mixes.

The consistent observation is

Primarily organic mix = roots on outside of pot and not much on inside.

Primarily diatomite or akadama = roots all through the mix.

I have found the akadama staying too wet and the roots were not in as great shape as in the diatomite mix. But it was a better sight than the trees I pulled from the nursery bought mix.

One pine I have had planted in a collider in akadama and v coarse sand. It's root mass was exceptionally dense. The air pruning of the collider was obvious.

This post is an interesting read

I have recently taken out some ground layers from a Azalea in a grow box.
The mix was fairly open, the finest particles being the 0.5-2mm Zeolite.
After about 2 years of seamungus and blood+bone the top although still open is sort of fudgy.
The roots on the layers that were taken out were nice and healthy in this mix.

Other plants that have been repotted have had some noticeable dead patches where the side of the pot was exposed to heat over summer and the regrowth of roots into the drainage layer.

A smaller pot 200mm squat pot containing another Azalea had a coarse mix with zeolite fines had roots everywhere. Top, bottom and in the middle. Like the grow box it has a fudgy layer on top from fert application and decomposition.

The mix in both pots was roughly 50/50 organic/inorganic.

I do notice in other pots with coarse mixes newly potted are devoid of roots in the top section.
The Sphagnum moss does do a terrific job in aiding root growth in coarse mixes or as a mulch layer.