Do these trees need alkaline soil? I used bark in all my mixes and I think the soil turned a bit too sour after a couple months. And can they withstand chalk? I have horticultural chalk (something like that) and I could dilute some wood ash in water which should also raise pH. Of my Korean Hornbeam, Oriental Hornbeam and Field Maple, I am most convinced that the latter is suffering from this issue. The leaves got lighter and lighter during the year. Dont have any pics to show.