Hi Smoke
I always liked the KISS principle (Keep it Simple Stupid) so I am happy to take this advice from people such as yourself and Walter Pall who states "Use whatever fertiliser is on special and with our free draining mixes the tree will use what it wants and the rest will be washed away"
Recently though I was reading an article from Walter Pall on Hornbeam care Bonsai Today 70
Watering
.... However the hornbeam reacts with some sensitivity to high content of salts in the soil mix, which shows up as brown borders on the leaves, If it is watered very frequently (in the case of a soil mix that dries out rapidly), to be safe it is preferable to use rain water instead of water from the faucet.
Maybe this needs clarification from Walter but I take "a soil that dries out rapidly" as a free draining mix. The teaching these days is that a free draining mix is able to have the salts washed away. I had to give this alot of thought. Especially since I believe Walter is one who has suggested that salts will just be washed away in a free draining mix and that is what I have aimed for especially with my hornbeams in our hot climate.
With some thought what Walter states in his care for hornbeam did make some sense when thinking in an extreme abstract manner. If you had a sponge that you watered once in a year and it took one year to dry out compared to a sponge that you watered 3 times a day for a year with it drying out each time in between. Just like a leaking pipe it makes sense that no matter how much you flushed the sponge out there would have to be more salt buildup residue in the frequently watered one.
Although I believed advice that any drinking water was OK for bonsai and our water is not bad anyway, I now believe that salt buildup is a major factor in the margin leaf burn I have been trying to cure in my hornbeams.
Rain water and careful monitoring of only using fertiliser that the tree needs seems to be the obvious solution. If the tree only needs P:K will I save on salt residue/buildup by using a 0:10:10:
Although I wish we could just keep it simple I think as with everything there are exceptions to the rule.
The Demo I went to see Peter Adams at in Australia recently (less than 12 months
) He was pushing organic fertilisers and seasol alot. Maybe fish emulsion. I will double check the notes.
This is my unfinished theory so I look forward to any thought anyone might have!