Tauranga - I have a 25m/sq lawn which at the end of the 2020 lock down I had killed off and Tall Fescue instant lawn put down by lawn professionals??

At one end is a large deciduous Cherry Tree. This shades a ⅓ of the lawn. The professionals stated that Tall Fescue was the correct grass seed for Tauranga climate and my lawn area, including the shade area under the Cherry Tree. Three years later I now have a very patchy soily area on that ⅓ of lawn.

We will not be chopping down the Cherry Tree!

This started to occur in the 2nd year of the new lawn. The rest of the lawn is very good. Since then I have tried all sorts of Fescue mix blends - Tall, Fine, Chewing and Creeping Red. I have overlaid the new seed with Daltons Premium Lawn Soil or/and Tui LawnForce® Lawn Preparation Mix. I have correctly used numerous brands of lawn fertilisers. I have even used our used coffee grounds. I also have some Earth Worms which I believe are good for aeration. I mow to a min height of 50mm in summer and 70mm in winter using a sharp bladed electric mower.  I hand water when necessary. (Not these days though. 🌧)

I have also just discovered via a pH probe that my soil is too alkaline (7.5-8.5). So on the weekend I applied a mix of liquid Sulphur, iron chelate and Sequestron, then retest in 4 weeks.

Of course the next period to sow is March - April.

I am thinking maybe I should change to a Tall Fescue and Kentucky Bluegrass blend or Tall Fescue and Soft-leaf Buffalo blend.

What are members thought for lawn seed in shady areas ??

Thanks.

EDIT: Refer to below post ref mowing heights - Thanks to tdgeek for pointing out this.