Carpinus leaves brown and shrivelled

Question

I grow bonsai as a hobby, for almost ten years now, and to get new material I often just collect some seedlings or saplings in the neighborhood. They are from the side of the road or other "wild" and "rough" spots here in the city of Amsterdam (Netherlands).

Last year in summer I collected some small oaks, hawthorns, field maples and this hornbeam (Carpinus betulus), most of them yearlings I guess. All these saplings are doing great, they survived winter (was not that cold), and have gotten their leaves back since spring. However, the hornbeam is the only one that is not doing well, the leaves are turning brown quickly and shrivel (see image). What is wrong with it?

I have all these saplings in pots with drainage holes, with fresh potting soil, and they are placed next to a south facing fence, so enough sunlight for most of the day. The rest of my saplings are doing great, so it is only this Carpinus that is having problems, but I don't know what. I water them when I see that the top of the soil is dry (that is almost every day, except for rainy days). Can it be too much light? Does hornbeam needs shade as a sapling? Too much water? Or are there other factors that Carpinus needs or can't stand compared to the rest of the trees?

The temperature the last weeks were between 15-20 C at day time and not lower than 5 C at night.

Answer 1

Hmmm, I will have to restrict my comments to experience with C. caroliniana which I have on my property in Canada. When resident in UK I don't recall any naturally growing C. betulus so not really familiar. My hornbeam grows only in one area characterized by a U shaped ravine which collects a lot of water and humus from leaves washed down from the upper slopes. I note too from the wiki page for C. betulus "They are found on soils with moderate clay content and avoid soils with particularly high or low clay content."

Putting these together I would say that constant moisture is a requirement; this can be achieved by a watering schedule which might be too frequent for other species, plus mixing the regular potting mixes with other materials which would slow drainage down rather than speed it up. Since you are a Bonsai person you will be familiar with Akadama which as it ages produces fine clay like particles that would hold moisture longer than say sand or peat. So how about try making a special mix for the Hornbeam with discarded bonsai mix added to what you are currently using as soil for the hornbeam? Also take care that when watering you do not flush fine particles out of the mix which frequently happens in commercial situations. Maybe keep the hornbeams separate and with a deep container water with ebb and flood process, reusing excess water with the fine particles in suspension.