How Bad is Rot on This Euphorbia polygona?

[MikeInOz]

@MikeInOz What do you think about the idea of using pure pumice for the new soil mix? It is a Euphorbia, and I will be keeping it outdoors in zone 9a, which is always a potential risk. It is already living outside in zone 9a, so no major climate change. But I would like to put the plant in a position to survive some lower temperatures.

I think using pure pumice would be ok but I would recommend removing as much of the original soil from the roots as possible with a root hook or even washing them clean. When the original root ball is in a finer mix than the new material it hold much more water and you can end up with a disaster.
The good thing about pure pumice would be that you could use a large pot without worrying about the unused mix going ''sour.'' Then all you need to do is throw on a handful of osmocote and you're home free...

[pone]

@MIkeInOz could you clarify some of what you say as follows?

You said "When the original root ball is in a finer mix than the new material it hold much more water and you can end up with a disaster." I do always wash the rootball clean when I do a replant, but if I did not do that why is a clay rootball in a pumice container worse than a container with all clay?

You said "...without worrying about the unused mix going "sour."" How can an unused mix go sour? Can you give some examples?

[MikeInOz]

pone post_id=377075 time=1597553847 user_id=16047]
@MIkeInOz could you clarify some of what you say as follows?

You said "When the original root ball is in a finer mix than the new material it hold much more water and you can end up with a disaster." I do always wash the rootball clean when I do a replant, but if I did not do that why is a clay rootball in a pumice container worse than a container with all clay?

Because there would be a more even moisture through the mix instead of always wet around the roots and dry further out. In other words you don't get good movement of water from fine to coarse.

You said "...without worrying about the unused mix going "sour."" How can an unused mix go sour? Can you give some examples?

When you have organic components in the mix and no root activity, the mix undergoes changes which no one really has accurately defined but it probably has something to do with a build-up of undesirable soil flora. One thing is for sure, roots do not like to enter! You won't have that problem with pumice because it's inert.
Basically all this means that you want the roots to touch the inner wall of the pot as soon as possible if you have a lot of organic content, and you want a mix which is courser than a plant normally would see in the ground.

[pone]

I have this plant elevated on a crane and I worked to get the clay soil off the roots today. The photos below show the roots after washing. Instead of a root rake, I used my hooked finger and dug up under the plant and started to pull down as many individual roots as I could. I have lost about 20% of the roots so far. I also used a machete to split open the root mass on the bottom so I could start this procedure. How far do I need to take this to get the roots clean? The rootball is very large, and I am sure there are sections stuck in mud/clay up higher in the rootball. Since it is all so dense it is hard to know when I have gotten all of that old soil out. I know it looks very clean from the outside looking up, but there is a lot of unseen space beyond what the camera is able to capture from the outside.

I assume it is okay to leave this plant bare-rooted like this for a week, allowing the roots to begin healing before I replant it in pumice?

2020-09-04 18.30.29 (Custom).jpg (116.77 KiB) Viewed 1771 times

2020-09-04 18.29.17 (Custom).jpg (84.56 KiB) Viewed 1771 times