if you dig a hole in mother earth.. and amend the soil in that hole.. in effect your are using mother earth as a pot filled with un-natural soil ... just sounds like a lot of work and cost.. and potentially leading to more problems than solutions...

my short rule is.. NEVER amend a planting hole ...as you are creating a condition in the hole only.. and if well tended.. the plant should grow roots right out to the hole planted.. so what was the point of amending it anyway ...

you shouldnt need different PLANTING rules for different plants... according to name...

though in this case.. dealing with the pH issue is not really a planting issue... its a cultural issue ... is you see the difference ...

ken

notice section one.. august is not really a planting time fro trees and shrubs .... so i hope you are talking now.. but not acting for another month or so ... by mid sept.. night temps are tending toward cold.. so the plant can recover from whatever stress a fall day throws at the transplant ....

https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub

@floral_uk z.8/9 SW UK I left out important details so I edited the post to make this clearer. I am building a large circular stone wall that will act as a raised bed, So I have some opportunity to create a hybrid soil mix that is more organic in the raised sections.

In any case, even for a pure container situation, have others noticed that this genus prefers heavily-concentrated bark soils?

@ken_adrian Adrian MI cold Z5 I won't be planting until late September.

I am not a big fan of adding heavy organic content into a planting hole. That would result in a "bathtub effect" with a highly moisture-retentive organic mix potentially under the water table of the surrounding soil, exposing the roots to too much water.

I think a purist doing an in-ground planting would say to get a soil test, then amend with just the minimal amount of organic material needed to correct any organic matter deficiency in the native soil. Since extremely fertile soil normally does not have more than 10% organic matter, that would be absolutely minimal amendment in the worst case.

My situation is different, with an enormous mass of soil sitting above the ground level, and guaranteed to be above the water table, because I am using a very high raised bed behind a retaining wall. I, therefore, have the opportunity to create something more like container soil, rich in organic matter, that will never become a water trap and death sentence for the roots.

I know some people do not like to create huge soil layer changes from organic to clay, on the thought that the roots may not want to penetrate into the deeper soil layers. This particular species/hybrid is not a very large plant, if you even want to believe that trees do not deal with changing soil layers all the time in nature. If you go to a place like Texas, in many places like Austin the top two feet of soil are organic matter, followed by three or four feet of heavy clay, followed by rock very near the surface. I think nature deals with such situations all the time, and trees are smarter than people when navigating such issues.

As long as media for conventional container culture is not made with anything phytotoxic, the key element is media's structure. It's probably not so much that poms like bark because they find it oh so chemically satisfying; rather, it's more likely they relish the physical attributes offered by the bark - lots of aeration and little to no perched water, depending on the volume of fine materials in the mix.

This ^^^ is a handful of the soil in my raised beds. It is comprised of at least a 75% OM in the form of southern yellow pine bark and reed/sedge peat. It works very well - everything I've grown in it has done exceptionally well, from trees to tomatoes. The two drawbacks are, it requires frequent watering (Earth is a pretty big wick), and there is a considerable amount of shrinkage (gassing off) from year to year. If I was to build additional beds, I'd go lighter on the OM, maybe limit it to 30-40% of the o/a volume. Fortunately, I repot as many as 150 trees yearly, and the used gritty mix has been incorporated into the soil. The added screened Turface and grit has notably changed the ratio of OM to mineral material over the last 20 years or more, which has resulted in a reduction in the amt of shrinkage and an increase in the amount of water I must supply.

I think, from the perspective of plant vitality, it's hard to have too much OM in a raised bed, but as a practical matter, you'll likely not want to deal with the shrinkage and keeping up with watering.

Al

@tapla (mid-Michigan, USDA z5b-6a) I appreciate your comment about soil structure versus chemistry. But I wonder if chemistry is also not part of the issue. Let me give an example with Rhododendrons. They do poorly when I plant Rhododendrons in a heavier sand soil mixture. If I substitute the sand for sized bark, they do exceptionally well (at least until the bark degrades and nitrogen is robbed). Assuming I took the time to make the perched water table in these two soils similar and assuming they both have good water retention and oxygen saturation, both soils appear to give a similar "structure" to the Rhododendron roots. If not, then the differences in structure are something subtle and involve concepts I do not understand well.

You have done it in other places here, but maybe you could document here what is the composition of your current raised bed soil, as you originally made it. Then maybe document how you would make it today if you were starting over.

My raised bed formula is similar to yours with one difference. But I want to defer discussing that until I see the details of your formula.