We were given a magnolia Susan as a gift in a small pot. It was growing indoors to keep it out of the cold weather but when the weather improved we moved it outside and also repotted in a larger pot with ericaceous compost. In just over a week the leaves started to lose their colour and go almost transparent, a week later those that had then dried out and are falling off. I've tried not to over water it and the root ball was planted following advice. I can't find anything on the internet that sounds like this so just wondered if anyone knew what the problem might be.
This looks like sun damage or sun scald to me. When a plant moves from indoors, or even a greenhouse; it's best to harden off the plant. This means moving the plant to the outdoors and letting them adjust to the outdoor sunlight conditions slowly, over a period of a few days to a week.
Shade the shrub from the hottest part of the day until it is established.
This shrub does best in full sun to partial shade. It requires an evenly moist well-drained soil for optimal growth, but will die in standing water. It is not particular as to soil type, but has a definite preference for acidic soils. Consider applying a thick mulch around the root zone in winter to protect it in exposed locations or colder microclimates.