I’ve got two Pittosporum Garnetti’s. One has just been planted but the leaves are going yellow and dropping off, it’s in a large pot 21”square. The other one which is 5ft tall and cost an arm and a leg, was planted last year, the leaves are browny/red on the outside and the overall appearance is darker. However, it has got new growth on its tips. When I plant new plants I always use a good tree and shrub compost with Vitax Q4 and Michorrizal Root Powder and water well.
Certified GKH Gardening Expert
Make sure that you cut this compost with potting soil, or it could be way too "hot" for the shrub. This would explain the burning, or dropping of leaves.
The next concern would be how much drainage the container has, and how much water was used. This could also be symptoms of a fungal infection, which can happen when soil remains saturated for too long, or sits in excess water.
I also recommend dolomitic lime added to the soil to keep the pH stable. Wettable sulfur will kill off any harmful microbes, as well as keep the soil conditioned to prevent bad infections.