We have a pittosporum hedge and I would like to mulch the prunings and use them on our garden. I have been told that using fresh pittosporum mulch is not safe but I can’t find out why not.
Pittosporum has a survival mechanism that 'selects' who gets to eat its leaves and who shouldn't. Some animals find it horribly bitter and others are attracted to the chemistry in this plant; Pittosporum Click on 'Resins' as well within the article.
There is a more important aspect I would like to point out. Non decomposed organic matter HAS to be decomposed before soil organisms are able to eat it, poop it, mix it in the soil. Your kitchen scraps, weeds, leaves, tiny branches, shredded cardboard should all be put in one area to decompose together. Add a little nitrogen to aid the decomposition. Keep moist not soggy. Decomposers have to have nitrogen for energy to do their job. Once the decomposers have thoroughly decomposed the raw organic matter the chemical composition has changed dramatically. Decomposed organic material will not look like the original material at all.
Fresh or non decomposed Pittosporum leaves would be cause for concern.
I can't tell you exactly why right now, chemically, grins but someone will add far more information to answer your question, might be me but I wanted you to stop throwing scraps of stuff on your beds. Far better to have a composting area with a few different piles, be able to turn and aerate the piles. Throw some nitrogen into the mix to 'feed' the decomposers.
Also, this is an attractant for rats, mice, possum, raccoon, deer...birds...bear. You can easily cover your decomposition piles to control moisture and aeration and minimize free loaders. Place your compost pile as far as you are able from your garden and home.