Adjusting fertilizer down, as substrate's CEC goes up?

[SU2]

Over the years my substrate-mixtures have changed, trending towards ever-higher percentages of pine-bark mulch (was originally shredded mulches, but found myco just prefer the 'mini pine bark' nuggets the best & colonize them the quickest)

I should mention the context of my nursery is that of "bonsai development and not refinement", I fertilize like crazy and use large containers; I do not give a second thought to internode length, since the branches being grown are to be cut-back aggressively, again & again, through their development (well, to be precise, some are actually getting pivoted to refinement treatment this season but most are not)

SO.......if my substrate went from mostly inorganic, VERY low CEC value, to one where I'm using 50%+ pine-bark-nuggets, then my CEC is now far far higher, which - at first - makes me think "You shouldn't fertilize as much because, now, more fertilizer has been retained", but - on the other hand - I also understand that pine-bark is in the process of decomposition and, therefore, it itself REQUIRES nitrogen; it is a nitrogen-sink itself.

How would you look at your fertilizer #'s if growing this way? For what it's worth, I never really reduced or changed my fertilization regimens while I was doing this and growth has still seemed just fine (have begun to think I could probably use 100% bark for certain species, I mean with Bougies they would hate that it'd be too wet but for instance this year's BC's & Maples are going into a mix that'll be ~70% bark, 20% styrofoam and 10% lava rock or perlite)

 

[SU2]

I also will say I worry about pH, whether I'm making things too-acidic this way....

I should've been clear - figure this goes w/o saying, but: this isn't just out-of-bag bark, it is properly screened and rinsed til it runs clear, actually I "prepare" it in advance I have large buckets of prepped bark that I put a few handfuls of tan sphagnum and a cup of organic fert (feather/bone/etc meals) on top of, and cover with a screen. These get rained on and I kinda 'stir them up' when going to get some for potting-up a tree (well, for adding-to the tree's old mixture, I usually like to keep as much of its old mix as possible, although I do rinse it for fines)

 

[Shibui]

For nearly 20 years I have used a mix with 70% mini pine bark but with propagating sand and some zeolite as the other fraction.
There is certainly some nitrogen draw down by the organics. Some argue that it will just be released at some stage so no real net effect but I do see occasional N deficiency if I don't keep up with fert program.
Not sure whether more fert or less is appropriate but it should be reasonably easy to set up some test pots and use less, normal and more fert to check the response of the trees.

 

[hemmy]

I should mention the context of my nursery is that of "bonsai development and not refinement", I fertilize like crazy and use large containers;

In my experience of developing trunks and often repots for nebari development, the fresh bark does not appear to break down to a point to impact root health or drainage before it is changed during the repot. Nitrogen deficiencies also have not been an issue, with a moderate chemical and slow release fertilizer program.

I also will say I worry about pH, whether I'm making things too-acidic this way....

I would be amazed if an acidity from the mix gave you problems, unless you are watering with an acidified water. If your location is FL, isn’t your water hard with high alkalinity?

 

[SU2]

For nearly 20 years I have used a mix with 70% mini pine bark but with propagating sand and some zeolite as the other fraction.
There is certainly some nitrogen draw down by the organics. Some argue that it will just be released at some stage so no real net effect but I do see occasional N deficiency if I don't keep up with fert program.
Not sure whether more fert or less is appropriate but it should be reasonably easy to set up some test pots and use less, normal and more fert to check the response of the trees.

"Some argue"...that's a silly argument me thinks! I mean, once nitro-addition to "balance things" is achieved/optimized.

So cool hearing it put the way you did, your reply here meant a lot thank you Yeah I actually think I may have nitro-chlorosis on some of my bougies then because acidity, mag and iron were all ruled-out as variables (yes pH was proper with Fe & Mg+ feeds, also do plenty of rainwater flushing from my ~200gal rainwater collect station) and just couldn't get rid of their chlorosis, will do testers with more & less nitro than-normal am surprised I didn't think of that

In my experience of developing trunks and often repots for nebari development, the fresh bark does not appear to break down to a point to impact root health or drainage before it is changed during the repot. Nitrogen deficiencies also have not been an issue, with a moderate chemical and slow release fertilizer program.

Gotta say I'm a touch uncertain why you replied this way to the quote of mine you'd posted but I wouldn't have suspected root damage I guess my biggest fear after finding myself moving towards these nearly all-pine mixes (again, they are very well-screened/rinsed and most containers are mesh-bottom or outright growbag/colander/etc types), was the high CEC would make dosing ferts very very difficult (it almost makes immediate-release "timed release" in a sense, since after drenching a container with 24% nitro it could rain hard twice and the bark would certainly still have some of that artificial nitro in it)

But just hearing @Shibui saying that made my day / season in this regard because damn the stuff is so great I kept thinking "I must be missing something because otherwise this would be more normal" but now I think it's just not as normal because most have suuuuuper thin shallow pots (whether or not their tree is actually show-ready, of course), really glad to hear someone doing it for decades who does it. Really it just ends up being like some kinda "super orchid-mix" when I'm done, actually even though I screen I usually toss a fistful of unscreened 'myco-soil' into the works just to inocculate it a bit more than nature/air already does

I wonder if anyone else "ages" their substrates? ;D Since BC, Maple & Nyssa collections are mere weeks away, I've got buckets & buckets with processed pine bark(why do the myco prefer this over all other mulches??) that have sphagnum & jobes organic fertilizer on top just dripping-down every time it rains

 

[hemmy]

Gotta say I'm a touch uncertain why you replied this way to the quote of mine you'd posted but I wouldn't have suspected root damage

I don’t know either! I think I meant to grab the part about bark decomposition and N2. I was just adding that in the short term (1-2yrs) in nursery cans, I don’t see any negative impacts from the bark breakdown. A bark/pumice mix can still be quick draining and have a high air-filled porosity, so regular fertilizer is still required (in my experience).

I also wonder how climate impacts the bark decomposition. I wouldn’t think humidity would matter much, since the moisture level should be similar if watering correctly. One study listed the optimal temperature range for max fungi and bacteria activity at 77F - 86F. My cool coastal climate struggles to hit that with our average highs at 73F. Of course, pots in the sun would get hotter.