Split off from my bonsai bit the dust.

[63pmp]

Just because it is inorganic doesn't mean it cant hold too much water. Air filled porosity is very much dependent on partical size. Though I suspect that microporosity of soil components affects surface tension and thus lowers AFP.

Particularly with shallow pots. You can fertilize in winter, just not after root pruning.

Paul

[shibui]

I'd like to raise issues with several of your recommendations Paul,

Resolve this by covering heavily root pruned plants (you cannot root prune J maples as hard as trident maples) with a plastic bag and keeping the plant in full shade,

high humidity and lack of sun is detrimental. I have lost many Japanese maples in those conditions. I believe most succumb to fungal infection which is more prolific in damp, dark conditions. My recently root pruned trees seem to do better with good sunlight and good air movement.

you cannot root prune J maples as hard as trident maples

What use is comparing one unknown with another unknown? Unless the reader is aware of how hard tridents can be pruned this statement must seem meaningless to any beginner. I think advice in concrete, measurable terms is far more useful.

or use a gravel layer in your pot.

. We have seen several interesting threads on this subject on Ausbonsai and I'm convinced that drainage layers can actually impede good drainage. gravel layers are a leftover from when garden soil was used as potting medium so a drainage layer provided the only source of air for the roots.

Your cultural practices obviously work for you but may not be universal. We have a very varied climate and everyone has slightly differing microclimates and methods, all of which impact on what will work for them at their location.

[63pmp]

I'm glad someone is asking good questions. I'll try and answer as best I can.

high humidity and lack of sun is detrimental. I have lost many Japanese maples in those conditions.

I place mine under 50% shade clothe, that is in shade from a gum tree after 1-2 pm. There is lots of air movement as the shade house is open on 3 sides

I believe most succumb to fungal infection which is more prolific in damp, dark conditions.

We are talking about maples repotted in late winter early spring going into bud burst. It is possible for them to get anthracnose on stems that have been frost damaged and cut with dirty shears, and they are susceptible to Pseudomonas as well. It is important not to allow the stems of the repotted tree to remain wet/damp. But generally, J. maples die from the roots up, the crown will blacken from cut tips down, but this is because the roots cannot supply water and nutrients. And main reason they die from the roots up is ponded water somewhere within the pot. Simply letting a pot sit in water on a solid surface will do it.

You do not wrap the trees in plastic like a Christmas present, you drape a bag over the top of the plant and leave the base of the pot uncovered and the surface of the potting mix uncovered. You can punch a couple of 5-10 mm holes in the top of the bag to release hot air if it gets some sunlight on it. The whole idea is to reduce transpiration stress, the trunk can dry out very quickly after root pruning.

My recently root pruned trees seem to do better with good sunlight and good air movement.

This creates transpiration stress, at a time when roots are not so good at pushing water. But if it works for you go for it, maybe one of those micro climate things. Where I live I cannot put black pines out in the sun after repotting, though I know this if often recommended.

you cannot root prune J maples as hard as trident maples

What use is comparing one unknown with another unknown? Unless the reader is aware of how hard tridents can be pruned this statement must seem meaningless to any beginner. I think advice in concrete, measurable terms is far more useful.

Here is how I treat trident's harshly; all these trees survived repotting and root pruning, you will have to take my word on this. This degree of root removal is simply to push new roots for nebari development, but I often prune tridents like this.

IMG_1658.jpg

IMG_1690.jpg

This is how I would root prune a J maple harshly, though I would probably reduce the larger roots by about another centimeter. ( I know this is picture of the trident above, but it was all had handy at the time, I rarely photograph routine stuff,but I think it gives the basic idea.)

IMG_1686.jpg

Additionally, I always, always, trim the edges and face of cut roots >2mm with a very sharp knife.

I hope this clarifies harsh root pruning.

We have seen several interesting threads on this subject on Ausbonsai and I'm convinced that drainage layers can actually impede good drainage.

Yes, the perched water table phenomenon. This research in Australia came out of CSIRO and was done by Kevin Handrek, who wrote a very good book called "Growing media for ornamental plants and turf" an essential book for people making there own potting mixes. As someone who trained as a soil scientist, I think about this a lot, and for many years never bothered with a drainage layer. The last couple of years I have started using them again, especially with Japanese maples. Firstly, I use a course medium of 70% perlite and 30% zeolite, sieved over a 2.5 mm mesh, and under a 5mm mesh. This has a very shallow saturated layer. And secondly, perlite has high water holding capacity within the granule that roots can access, so I'm not watering all the time. I only water once a day or when the plant needs it, (maybe once every four days in winter), and twice a day when temps go over 33C, but that's my micro climate, it will be different for different folks. The gravel not only allows air to penetrate under the roots and potting media, but also speeds up the drying of the perched water table as well, reducing its impact.

Your cultural practices obviously work for you but may not be universal. We have a very varied climate and everyone has slightly differing micro climates and methods, all of which impact on what will work for them at their location.

[/quote]

Yes, micro climates are important, but I believe this approach can be used universally, and especially in KC's climate.

Thanks for the good questions, I hope this explains things a bit better. I often find myself time poor and forums, for me, are not a good way of explaining complex concepts.

Paul