I would instead suggest a soil-less aggregate medium, such as calcined clay gravel or expanded clay beads, with a pulse irrigation schedule for a hydroponic solution. This way, you have excluded soil-borne pathogens as well as ensured physical support, nutrients, and oxygenation.
I've never planted Taxus baccata, but I never planted potatoes in aeroponics. roots development is very good, because aeroponics systems have good aeration.
Here is a picture of my research : about the roots of the potato in the aeroponic system in the lowland tropics