i have a few things in the yard doing such.. here in MI ...

we had 6 weeks of drought.. followed now.. by two weeks of good rain ...

can you check and see if this is the newest flush of growth ...

in my yard.. things are growing so fast.. that new growth often looks like this for a week or so ... while it is expanding and toughening up ...

lets rule out normal transitory growth before we go down the problem or disease route ...

BTW ... any info on the plant.. recent transplant .. size.. location.. soil.. etc .. might help... as well as a pic of the whole ...

ken

You have two threads going on this issue. This being the newest, I'll post here.

As noted, you don't say whether this plant started with you as a container grown specimen (came with all its roots) or whether it started with you as a B&B plant (truncated root system, needing recovery). That can inform opinions offered and recommendations therefrom.

Your soil pH would be interesting to know, but not necessarily germane to growing this species. Texts say it prefers acid soils that are well-drained, but I've grown it on absolute limestone soils to various circumneutral sites with well-drained to heavy B-horizon clay loams - like here at the Valley, where I've grown over a hundred of these, with the oldest now for over twenty years.

I really don't think that bit of yellowing is a matter for concern. It could be a nutrient deficiency that came with container culture; it could be a bit of heat stress that affected that set of leaves as they were forming. I would continue with some iron sulfate if your pH is circumneutral; it won't hurt a thing. Some 10-10-10 in spring as it leafs out and in summer will assist in establishment, as Aesculus parviflora is a gross feeder and robust grower.

Given your site description, I'm interested in how you plan to manage this as it matures. As a small canopy tree?

Here are some happy old Bottlebrush Buckeyes, doing their summer thing at the Valley...